26 More Water a jRid Lands

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romising Tech 1 : . f I i and */ I eseakh- Opportu Y? . .

** ..$N~~NAL ACADEMY OF sc~

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7, Water I 49 ._ for -=; ?. ‘. Arid’, “(

Lands >A ’ Promising Technologies ,

and .a I Research Opportunities - v

Report of an Ad Hoc Panel of the .$ AdeoIy Committee on.Technology Innovation

Board on Science and Technology for International Development Commission on International Relations

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‘\ RCsumC en Franqais \ \ Resumen en Espariol \

\-_ National Academy of Sciences ;

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This report has been prepared by an ad hoc advisory panel of the Board on Science and Technology for International Development, Commission on International Relations, Xational Research Council, for the Office of Science and Technology, Bureau for Technical Assistance, Agency for International Development, Washington, D.C., under contract-U-2584. “1

NOTICE: The project which is the subject of this report was approved by the Governing Board of the National Research Council, acting in behalf of the National Academy of Sciences. Such approval reflects the Board’s judgment that the project is of international importance and appropriate with respect to both the purposes’ and resources of the National Research Council.

The members of the committee selected to undertake this project and prepare this report were chosen for reco,tized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. Responsibility for the detailed aspects of this report rests with that committee.

Each report issuing fro-m a study committee of the National Research Council is rliiewed by an independent grotip o”f qualified- individuals according to procedures established and monitored by the Report Review Committee of the National Academy of Sciences. Distribution of the report is approved, by the President of ‘the Academy, upon satisfactory completion of the review process.

Library of Congress Catalog Number 74-10058 . .

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b’ ‘“’ Panel on Promising Technologies in Arid-&r$Water Development - \ . r

DEAN F. PETERSON, Vice P&sident. for kesexrch, Division of Research, --Utah State University, Lo&n,%tah, Chair-man _

FALIH K. ‘r$,JIBURY, Soil Physicist, Agricultural Extension, University of , C&f&a;P$ulier, C ’ a!!& mia

BAvzF...$ILLY, Executive Manager, Navaj.0 Tribal Agricultural Products _- ,‘7 ,F ‘tidustry, Farmington, New Mexico ./

C. ,BRENT CLUFF, Associate Hydrologist,. Water Resources Research Center, Universigrof Arizona, Tucson, Arizona

HAR,OLD .i?, DREGNE, *Chairman, Department of Agronomy, Texas Tech . .. University, Lubbock, Texas

EARL A. ERICKSON, Department o$ Crop and Soil Sciences, Michigan Statk University, East Lansing, Michigan. c * ‘, /:

.;’ MICHAEL EVENARI,‘B~~~~~ Department, Hebr&r University of JLerusalem, jl .’ , r Jeiusalem; Israel .’ -’

-G, t . u 1 ;I -. JEROME GAVIS, Department of Geography and Environmental-Engineering,

The Johns Hopkins University, Baltimore, Maryland 2. . . ROBERT M. HAGAN, Department of Water Science and Engineering,’ .

University of California, Davis, California s., * JACK KF~LER, Agricultural and Irrigatitin @ginee&g Departmknt, Utah

%&cUn.&e~~ga~ I&ah--.. ~. -L-p_ ___-- ~ --- . . -2-c 7.-,---*-.p /e FERNANDO MEDELLiN LEAL, Director, lnstituto de Investigaci& ‘% ”

Zonas DesCrticas, Universidad Aut6noma de San Luis Potosi, S. ~-L. P., Mexico

LLOYD E. MYERS, U.S. Department of Agriculture, Agricultural Reseaich ‘:, Service,-Western Region, Berkeley, California _ _

SOL D. RESNICK, Director, Water :pesources Research Center, University of ., -. Arizoqa, Tucsbn, Arizona 1 I “n,p

JAN VAN SCHILFGAARDE, Dire&or, U.S. Salinity Laboratory,. Soil and . ’ ‘i \ L \

Water Conse$ation Research &vision, A.R.S., U.S. Department of Agriculture, Riberside, California ]

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NOEL’ D. VIETMEYER; Ej0iid 0n~~S~~~ iende and Technology for*Internatioi8l’ ~‘,w*:’ Development, Commission on Intbmational Relation$#ational Academy - - .

. of Sciences-National ResearchXotncil, StaffStudy Directqr s

i JOLIEN. ENGEL, Head; Special’Studies, Board on Science and Technolow \

: for International Development i ‘, . .

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Contributors’ ,

LEON BERNSTEIN, U.S. Salinity Laboratory, A.R.S., U.SL Department of ’ Agriculture, Riverside, California.

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KEITH R. COOLEY, U.S. Water Conservation Laboratory, A.R.S., ‘U.S. .’ Department of Agriculture, Phoenix, Arizona.

ALBERT K. DOBRENZ, Department of Agronomy and Plant Genetics, c University of Arizona,gTucson, Arizona. r. r

A. RICHARD ~KASSANDER, JR., Vice President for Research, ‘University of Arizona, Tucson, Arizona.

L. K. LEPLEY, Office of Arid Lands Studies, University of Arizona, Tucson, Arizona. I

MARTIN A. MASSENGALE, Department of Agronomy and Plant Genetics, Uniyersity of Arizona, Tucson, Arizona.

JAMES J. RILEY, Environmental Research Laboratory, University of Arizona, Tucson,,Arizona.

W. T. WELCHERT, College of Agriculture, Cooperative Extension Service, University of Arizona, Tucson, Arizona.

L. G. WILSON, Water Resources Research Center, University of Arizona, Tucson, Arizona.

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Preface

-\ Little known but promising technologies for the use and conservation of

scarce water supplies-in arid areas are the subject of this report. Not a technical handbook, it aims to draw the attention of agricultural and community officials and researchers to opportunities for development projects with probable high social value.

The technologies discussed should, at present, be seen as supplements to, not substitutes for, standard large-scale water supply and management methods, But many have immediate local value for small-scale water development and conservation, especially.:in remote areas with intermittent rainfall. With further research and adaptation, some of the technologies may prove to be economically competitive with standard/methods of increasing the water supply or reducing the demand.

For t$e convenience of the busy reader, each technology is presented in a separate chapter, and the material is arranged under these topics:

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Methods Advantages

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Lirnitatiorrs’ ~--~~- ~ -~---, Stage of Development Needed Research and Development Selected Readings (a short list of review? and general articles) Contacts (a list of individuals or?org$nizations the panelists know to be

involved in relevant research) NOTE: Neither the Selected Readings nor the Contacts are meant to-be - .

exhaustive.

Several points deserve emphasis: The panel considers that all the technologies in this report have proved

themselves within the individual settmgs described. When these technologies are applied elsewhere, consideration should be given to unique local conditions that may affect their success. Questions should be asked that cannot all be accounted for in a general report.

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The particular choice of technologies examined in the report is not meant -. ’ . to reflect on others, which may be equally worthy of attention. Selection was based on technical merit and potential for application? particularly iii

’ ,developing countries, as seen by the panel. No order of importance is implied by the chapter sequence. Some methods selected tire ready for. widespread application; for others, the fundamental principles are still being devel.oped. Although most of the ideas discussed are not new, they have as yet had little . impact.

in its discussion of the technologi~, the panel took heed of their economic parameters but cou1.d not consider this subject in specific detail. Attempts to iestimate future cost in the vastly different economic and

. e’cological eni ironments L of the several dozen countries beset with the problem of aridity would have. bogged down the discussi&s, as would consideration /of political, institutional, and social factors. Accordingly, this report confin+ itself to a technical overview, le&$ng to the reader the task of weighing the~~t&chnical ‘prescriptions in the light @‘f h,is country’s resources and h capabilities.

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The, Ad Hoc Panel on Prom&g Technologies for Arid-Land Water /

-9 velopment formulated this report. at a meeting in Tucson, Arizona, in :

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0 tober 1973. Each selected technology was evaluated and written up before ’ ’ L the ting by an individual committee member, in collaboration with the

NAS staff; each paper was reviewed by the others, discussed during the ,, ,, ii meeting, and modified according to the will of the panel as a whole. This document, therefore, reflects a consensus. d

The panel is indebted to Tresa Bass- and Mary Jane Koob, ‘who acted as I , . administrative Sgcretaries for the meeting and for production of the report,, l.i

- ---a~~~M+B;-Richaib Kassand?; Jr-. ,~~a~D~-Jehnsof~~-U~~~~~-~“-“- = Arizona for local arrangements in Tucson. The report draft was prepared for ‘i

publication by Jane Lecht, and the Arabic translation by Mohammed Sageer. This project is part of an experiment to determine ways scientists and engi- ‘,

neers can make a more effective contribution to economic-development acti- ?. vities, particularly by translating recent research results into a usable form for

--.- _ ..- decision makers. .If you wish to~co@m+ on this rep-ort and especialiy if you ~...L . find it useful in your work, please communicate with the staff officer, Dr.

Noel Vietmeyer, NationGal Academy of Sciences - National Research Council, 361 Constitution Avenue, JH 215, Washington, D.C. 20418, USA., e.

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.t;y ; Two systems of ancient agriculture in the Negev-narrow terraced wadis and 1 farm units with small watersheds-show a most rational and wise use of’thg available natural resources. The ancient farmer fitted his artificially created. - agricultural ecosystems into nature and used landscape and topography to his

. best advantage without damaging,his environment. He neither caused erosion 1 ’ nor brought about salination of’his agricultural soils. By using the runoff he . tamed the flood torrentshand prevented, the damage that-uncontrolled floods i usually produc . He certainty did not,overirrigate-because his water-resources 0 ’

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,were*limited, a. in this case a.s‘in%.many others, limitation is the moth& ofi - ‘good management. The methods of the ancient” civilizations of providing ~ dr&king lyater are another example of a *most rational use -of nature’s resources. The same is. true of the [qanat], which merits our special adm.iration because of the ingenuity involved in its

environment and and sometimes improving

on it, This is most obvio& in the Most of the plant . associations of the natural water. A’good i observer will notice this’ and may apply this knowledge to. grow crltivated ’

--$ant-sto hisown benefit.. i __-- - - -A ~-. ._

‘i . .m_mmM&hael Eyenari, Leslie Shanan, and .N_apht&Tadmor.mm ,. ~~~ -

The Negev: The Challenge of a Desert. “--Y-- L “I

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INTRODU@?TIO.fJl AND SUMMARY

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SUMMARY IN ARABIC -

RESUME EN FRANSAIS

RESUMEN EN ESPANOL

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Rainwater Harvesting 9

Runoff Agriculture 23

Irrigation with Saline Water 38

Reuse of Water

Wells

Other Sources of Water ,

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WATER SUPPLY

WATER CONSERVATION

Reducing Evaporation from Water Surfaces 73

Reducing Seepage Losses 81

Reducing Evaporation from Soil Surfaces 87

Trickle Irrigation f 97

Other Innovative I rrigation Methods 105

Reducing Cropland Percolation Losses 111

Reducing Transpiration 116

Selecting and Managing Crops To Use Water

More Efficiently, 123

Controlled-Environment Agriculture 128

Other Promising Water-Conservation Techniques ‘135 -_

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-Advisory Committei! on Te’chnology I ngovation 150

Board on Science and Technology for International I

Development (BOSTI D) 152

BS>STI D Publications 152

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,’ Introduction and Shnmary .

Arid regions fi?oday face more difficult problems than ever before. The ’ 7 world’s sand deserts appear to be enlarging, and.droughts arc contributing to

the economic devastation of whole nations. The six drought-stricken Sahelian nations”Frovide, an ‘extreme illustration, but industrialized and developing coun$es both suffer from the crigis. The southwestern United States, for ..: example, faces falling water tables and increasing groundwater salinity.

/ Nevertheless; arid lands have. underexploited agricultural potential. We

;I/” hould learn that this potential can be best ‘developed by concepts and

/ methods specifically suited to dry regions. Water practices developed for

. ,//” /’ temperate climates may not work as well in arid regions for technological,

/ environmental, economic, and cultural reasons. We needfresh,. innovative approaches to water technologies, particularly those designed to meet the needs of arid regions in the less developed world, where there has often been improper application of practices developed in regions with higher rainfall or more abundant water supplies. Also, we need to‘ reconsider practices developed in arid regions by ancient agriculturalists. Basically, there are two . . approaches: increasing the supply of usable water and reducing the -demand I for water. Supply and demand, as well as delivery, have to be considered as an * integral system.

There are many possibilities for simultaneously~ increasing supply and reducing demand that together will bring benefit

P to arid lands. ,A major

opportunity to save water exists in conventional irrigated agriculture, by far the arid world’s largest user of water. This is,true for centuries-old, traditional systems as well as for large, capital-intensive *modern water-management systems. Conventional systems are not the main topic of this report, because’ they are extensively treatedelsewhere (Selected Readings, p. 5). Still the following points need to be made:

. i b In some arid lands the greatest opportunity for increasing water

$upplies is to improve -existing water systems and thus make more water available without a complete new installation. For example, replacing canals with closed conduits (of plastic, concrete, metal, etc.) will reduce evaporation, or lining canals will reduce seepage losses. (Most chapters in this report

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deal in one way or $otheriwi@ improvrnrie~~~~~~~~.~~a~~~ stems and _- the maximum u&ation bi- existing water supplies.) i

0 Significant amounts of water can be saved by improving water management on the farm, a topic agriculturalists in many areas qften’neglect. One deficiency is the design of on-farm distribution and drainage systems between farm fields, Storage, main, and diversion canals and main drains may be well

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en ‘neered (even down to turnouts serving one or two hundred hectares), but . . m st ditches serving farm fields are inadequate, sometimes even nonexistent. f Furthermore. the irrigator often mismanages applicati&n of the water.

* In designing new systems and rehabilitating old ones, the needs of the user should be paramount. The system must deliver the right amount of water to the user at the right time. Frequently,‘an irrigation project fails to reach its potential because the use-requirements for the water have not beep suf- ficiently considered. For example, the delivery system in irrigation should be , designed to permit changing the water supply as crop demands change with weather and plant matutiity. But water is often derivered in an arbitrary and inflexible manner.

* Where groundwater,is available, surface and groundwater supply and delivery systems should be considered in combination (conjunctive use) for optimal use of the total water resource.

0 Universally, farmers tend to overirrigate when.water is available. This can lead to problems of waterlogging and salinity, and leaching of fertility. Frequently, institutional arrangements (systems of delivery, scheduling, water-rights laws, traditions, etc.) encourage overirrigation. Although over- . irrigation may be needed to remove accumulating salts, recent studies indicate that the amount required may be much lower than was formerly believed (chapter .3).

* Conventional irrigation is neither cheap nor simple; complexities in the design, construction, and efficient operation of standard irrigation projects are frequently oversimplified or overlooked. Fields are often inadequately leveled, and even small undulations can waste large amounts of water. Pre- cision land-shaping and skilled labor are required. Grading land to a flat surface usually requires high capital costs for equipment, fuel, and maintenance.

l The scarcer the water, the greater the need for technical and management skills.

Chapters ‘1-6 of this report deal with technologies forVenhancing water supplies; the rest cover water conservation, A summary follows of the technologies in this report.

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INTRODUCTION AND-s.FyY‘ARY ‘~ .,‘<5 I. c

Rainwater Harvesting -

Rainwater collectedJfrom hillslopes and man-made catchments c8n create : new supplies of lay-COSJ, high-quality water for arid lands (chapter 1).

R&off Agriculture I” >

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Runoff agriculture involves rainwater harvesting; the water is used directly in agricultural systems-specifically designed for the purpose (chapter 2).

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Irrigation with Saline Water

Saline water is ,yidely available but rarely used because it restricts plant growth and yield. Evidence is now hccumulat.ing-that with ca’re and under

/ certain .favorable conditions, saline water can (be profitably used for irrigation (chapter 3). rl h

4 Reuse of Water

Increasing demands on water make it necessary to greatly increase water reuse. Technical developments such as recycling and advanced waste treatment may have great importance in the future (chapter 4).

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Wells .+ 4

Hand-dug wells, a technology begun thousands of years ago,. is regaining popularity with the help of new materials and construction equipment. Qanats and horizontal wells, methods for tapping underground water without using pumps, are also described (chapter 5)..

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Other Sources of Water

This chapter briefly mentions groundwater mining, desalting, solar distilla- i9 tion, the use of satellites and aircraft for detecting water in arid lands, rainfall augmentation, the possibility of using icebergs as a source of water, and dew and fog harvesting (chapter 6).

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Reducing Evaporation from Water Surfaces

Because evaporation is invisible, it is seldom regarded as a serious drain on stored water, bus annual evaporation losses, particularly in arid lands, are very great’. Evaporation reduction merits increased attention as a way to conserve water (chapter 7).

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Reducing Seepage Lo’sses

Seepage causes serious water losses in canals and impoundments. Mo’dcrn materials and techniques can reduce or eliminate seepage. but costs are still high (chapter 8). L

’ Reducing Evaporation from Soil Surfaces r_

Water losses resulting from evaporation from soil sur~faccs can b’e rcduccd by covers or mulches. In many cases the covers also scrvc complcmkntnry functions such as stopping desert cncroachrncnl or promotrng runoff agriculture (chapter 9). ‘..

TriFkle Irrigation .r’ 1 ?:

This newly developed irrigation method uses a system of plastic pipes placed on the soil among the plants. Water carried in the pipes d soil beside each plant at a rate carefully matched to the &ant’s pared with cunventional irrigation, csccllc~t crop yields have be with a minimum amount of water (chapter 10).

Other Innovative Irrigation Methods a

Sumc simple irrigation methods, ncglcctcd in technical manuals or tckt- books, with potential benefit for arid latds arc prcscnted pictorially (chapter *’ 11). A

Reducing Cropland Percolation Losses

Large areas of sandy soil in arid lands are* not used for agriculture because ‘the water sinks below the root zone too rapidly and the extra irrigation water . nccdcd to compensate for this problem is not available. Techniques are nay

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i; being developed to produce artificial underground moisture barriers to prc- vent or restrict water and nutrients from percolating away (chapter I?).

Reducing Transpiration

About 99 percent of the water absorbed by plant roots is.released into the- air from leaf surfaces. If practical means to reduce this process can be found,

raise a given major savings can be realized in the amount of water needed to crop (chapter 13).

INTRODUC’fION AND SUMMARY 5 !f ,

Selecting and Managing Crops To Use Water More Efficiently

Relatively little has been, done on designing water-efficient systems for * arid-land agriculture. Numerous research opportunities from planr genetics to . engineering ren:ain to be exploded (chapter 14).

Controlled-Environment Agricultur”e

When crops ;Irc grown within watertight bul tranSparcn1 cnzl~~surcs. rhc amount of wa~cr rrormally lost can bc greatI? rcduccd. and fhc atmaspl~;rc aru~lnd .~hc plants can bc manipulated to masimizc productivity.- Thcsc ;Irc costly systems, but high agricultural pruduc&vity can bc achicvcd with small amuunts of watci in very inhospi~ablc rc.gicins (cliaptcr 1.5). * I

‘Other Pro,gising Water-Conservation Techniques 9

This chaptcr‘briefly mentions water-ionservihg soil amendmcnk and artificial recharge of groundtiat,er. (chapter, 16).

Selected Readings

Arid Zone Rcscarch Liais’dn Ofliccr, C’ommonwcalth SXcntific and Industrhl Rcscartil@ Organization. Annual. lltid %orw h’~iu?lCff~r. (Booklet provides rcprcscntativc cross- section of arid-zgne rcscarch in progress in Australia. Available frbm the authoring institution, Canberra, ACT, Australia.)

Arnon. I. 19’72. Crop Production itz Dry.Rcgiotts. I’ollrr~w I: Backgrolrnd arid Principles. Barnes and Noble, New York; Leonard Hill Books, London. 650 p,

Bateman, G. H. 197 1. A Bibliography of Low-Co~f Wafer Tecllnolo,.es. Inte Mediate Technology Development Group, Ltd. (Pamell House, 25 Wiiton Road, I&don SW1 V lJS, England, Price fl .OO). 45 p.

Diuey, F. 1950. A Practical Handbook of Waty +pplr. 2nd ed. T. hlurby. London. International Hydrological.Decade. 1969. The Progress of Hydrolo,qt. Vol. 1, New De- I vclopmcnts in Hydrology, Vol. 2, Specialized Hydrologic Subjects, Vol. 3, Hydro-

logic I<clucalion and Discussions. Urbana, Illinois, USA. 1295 p. (Available from V. T. Chow, Civil Engineering Building, Room 3 118, University of Illinois, Urbana, Illinois 61801, USA.)

Jsrdelsen, 0. W., and V. E, Hansen. 1962. Irrigutiorl Principles aud Practices 3rd c‘d. John .Wiley and Sons, New. York. 447 p.

Kaul, R. W., ed. 1970. Af~orcstatiorl i/z Arid Zones. Dr. W. Junk N.V. Publishers, The I-Iab?le, The Netherlands. 435 p.

National Water Commission. 1973. ‘Irlater Policies for the Fu&re. Stock No. 5246-00006. Superintendent of Docum,ents, U.S. Government Printing Office, Wash- ington, D.C. 20402, USA. $79 p. (USS9.30).

Office of Agriculture, Technical Assistance Bureau, U.S. Agency for International Development. 1973. Improving Farm Production in Tropical and Subtropical Regions of Limited Rainfall. Technical Serie?,. .Bulletin Number 4. 25 9. (Available from authoring institution, Washington, D-C. 20523, USA.)

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6 MORE WATER l:OR ARID LANDS

Office 0 f Science and Technology, Technical Assistance Bureau, U.S. Agency for Inter- national Development. 1972. Desert Encropchnzerlt 012 Arable Lajlds: Significance, Curtses and Control. 55 p. (Available from authoring institution, Washington, D.C. 20523, USA.)

Office of Science and Technology, Technical Assistance Bureau, U.S. Agency for Inter- national Development. 1973. Techkques for Assessing Hjldrological Poterltials in Developing Countries: State of the Art arld Research Prior-itiLTs. Report No. TA/OST - 73-17. (Available from authoring institution, Washington, D.C. 20523, USA.)

Paylore, P. 1967. Arid Lands Reseti& Instiptions: A World Directory. University of Arizona Press, Tucson, Arizona 85721, USA.

Peterson, D. F. 1973. Irrigation Practices Seminars 1956-70: an Evaluation. Asia Bureau, U.S. Agency for International Development, Washington, D.C. 20523, USA.

Rhodesia Agricultural Journal. 1972. Water in Agriculture. Teclmical Bulletin No. 15. I’ 197 p. (Available from Department of Research and Specialist Services, Ministry of Agriculture, P.O. Box 8108, Causewab, Salisbury, Rhodesia.)

Water fok&ace: Proceedings .of the Internatidnal Conference on Water for Peace, ~@%asl&gton, D.C. 1967. 8 Vol. Stock No. I-.2; W29-5/Vl-8, Superintendent of

D&u?nents, U.S. Government Printing Office, Washington, D.C. 20402, USA. (USS60.00)

Water Research Foundation-& Australia. 1968. Water OII the Farm. Report No. 25. 59 p. (Available from authoring institution, P.O. Box 47, Kingsford, New South Wales, 2032, Australia.)

White, G. F., ed. 1956. The Future of Arid Lands. Publication ‘,io. 43. American Association for the Advancement of Science, Washington, D.C., USA. 453 p.

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Rainwater Harvesting

Though rain falls infrequently in arid lands, it comprises con?iderable amounts of water; 10 mm of rain equals 100,000 1 of water per lia. Harvesting this rainwater (FIGURE l$ can provide water for regions where other sources are too distant or too costly, or where wells are impractical because of unfavorable geology ‘or ex\cessive drilling costs. Rainwater harvesting is particularly suited to supplying water for small villages, schools, households, small gardens: livestock, and wildlife.

Ancient desert dwellers harvested rain by redirecting the water running down hillslopes into fields or cisterns (FIGURES 2-4). Modern farmers in arid lands have seldom harvested rainwater in this direct way, though in 1929 a 2400 m2 catchment in an arid part of AusmliatO mm average annual rainfall) provided adequate water for “6 persons, 10. horses, 2 cows, 1.50 sheep” even during the years of lowest ra.infall.1

Today. researchers are working to increase water runoff by modifying the surface of thcj soil. I

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Rainwater barvesting is possible in areas with as little as 50-80 mm average annual rainfall\: This seems to be the lowest limit, but duri,ng a year with only 24 mm of rain, a water-harvesting catchment in Israel still yielded a usable runoff.2 In some arid regions, such as the southwestern United States, snow and sleet also contribute to runoff water. Loess and loess-like soils, present in most deserts, are ideally suited for rainwater harvesting because after even a small rainfall they form a crust that promotes runoff. F-D&

Sometimes rainfall runoff can be collected from an untouched natural way is to dig ponds in small depressions where they can

(for example, the pond in FIGURE 48, page 84). Often the catchment needs modification, usually .by making the soil surface more

:Kenyon. 1929. (See Selected Readings.) Evenari,,Shanan, and Tadmor. 1971. p. 325. (See Selected Readings.)

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in MORE WATER FOR ARID LANDS

FIGURE 1 The yield from rainwater harvesting can be surprising. Here in the Negev Desert runoff collected from the background hills is channeled to the farm site and distributed to separate fields. (N. Tadmor)

impermeable to increase the amount of runoff. There are many methods, including the following:

Land Alteration . ‘.

In some cases all that is needed to collect and convey runoff water are ditches or rock walls along hillside contours (FIGURES 2 and 5). Clearing away rocks and vegetation usually increases runoff water (FIGURES 3 and 4); compacting the soil surface can increase it; too (FIGURES 6 and 7).

RAINWATER HARVESTING 11

FIGURE 2 Two thousand years ‘kgo Nabatean inhabitants of the Negev Desert built this chtinel across a hillside to harvest rainwater runoff. The channel leads water to a cistern at the right. A similar channel,~disappearing to the right, drains the slopes on thy other side of the hill. (L. Evenari) ’

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FIGURE 3 Ancient rainwater-harvesting system in the Negev. Gravel that covered the slopes has been moved aside, leaving a catchment that directs rainfall runoff to a farm in the valley. (M. Evenari) m

MORE WATER FOR ARID’LANDS

FIGURE 4 Aerial view of ancient gravel mounds and strips still used to increase the rainwater harvest from hillsides in the Negev. Unable to remove all the gravel, the Nabateans mounded it (shown by dots). Conduits and channels are organized so that each drams a small catchment. This system divides overall runoff into small streams, thereby avoiding (N. Tadmor)

With these excessive and 18

erosion and Ixesenting the farmer with small, easy-to-handle flows.

simple systems erosion is the main problem; when it is not ow-cost hillside land is available, these land alterations can be

very economical ways to harvest rainwater in arid lands. s

Chemical Treatment

I A promising method for harvesting rainwater <is to treat soils with chemicals that fill pores or make soil water repellent.

Sodium salts, which cause clay in the soil to break down into small particles (partially sealing the soil pores and cracks), can be used to increase

m RAINWATER HARVESTING

FIGURE 5 Harvesting runoff from rocky hill slopes. Total capacity of the two tanks is 110 m3; 75 mm of rainfall fills both tanks. Rowa African, Purchase Land, Rhodesia. (Rhodesia Agricultural Journal)

FIGURE 6 Western Australia rainwater-harvesting system. Catchments are graded and rolled and shed water with a minimum rainfall of 7.6 mm. They cost 530-$40 per acre (1968). They are designed so that for only 4.45 cm of runoff 1.6 ha of catchment fill provide 800 cubic’m of water. Catchments are cambered so that rainfall runoff quickly goes to the side*of the “road, ” where a ditch conveys it to the main-collector drain and thence through a silt trap to the storage tank. (Taken from Department of Agriculture of Western Australia, 1950. See Selected Readings.)

.

--

14 MORE WAT’ER FOR ARID LANDS

runoff from many clay-containing soils (chapter 8). Sodium salts are intrigu- ing as soil sealants because of their low cost, ready availability, and retarda- tion of weed growth (FIGURE 24, page 33).

Other commonly tried water-repellent chemicals are silicones, latexes, asphalt, and wax (chapter 9). Although much more research remains to be done, these sealants now appear feasible for use on stable soils that do not swell with moisture.

Asphalt offers promise for building low-cost, impermeable catchments, particularly because it can be easily applied by spraying. In the United States hillslope catchments have been cleared of vegetation, smoothed, treated with a soil sterilant and two coats of asphalt to make rainwater catchments. One coat seals the pores; the other protects against weathering. Asphalt catchments on suitable slopes have been found to last 4 or 5 years. Problems caused by unstable soil conditions, oxidation, and penetration by germinating plants have recently been overcome by reinforcing the &?phalt with plastic or fiberglass and covering the catchment with gravel.

FIGURE 7 A modern rainwater-harvesting catchment south of the Stirling Range in Western Australia. The average annual rainfall in this area is 500 mm, falling during seven winter months. Natural ground surface is sandy with a clay subsoil. The sand is moved into rows; the clay exposed by the roading process is-shaped and spread to cover the whole surface. The ridges discharge runoff water into a channel which conducts it to the square tank (capacity 3000 m3). Main advantages are that the system uses the existing soil and can be built with Feadily available’bqdipment. Smoothing and compacting the steep “road” surfaces is most important, h&e achieved by tractor and rubber-tired roller. The system appears suitable for many othet arid and semiarid areas. (D. J. Carder and M. Hollick) 9 ,

.

. . ., “L

RAINWATER HARVESTING 15

Paraffin wax has recently been used as a soil-sealant (FIGURE 8). Granulated wax spread on the ground melts in the sun and flows into the pores to produce a surface that readily sheds water. The wax can also be melted and sprayed on the ground. In tests,3 wax-treated plots yielded an average of 90 percent of the rainfall as runoff, compared to 30 percent from untreated plots. Runoff water from the wax plots had low salt content (less than 50 mg per 1) and almost undetectable organic matter. ._

Soil Covers

Instead of making the soil itself the water-shedding surface, it may be better i$some situations to cover it with a waterproof cover. On porous or

: unstable soils in particular, maintaining other methods would be too costly. Plastic sheet, butyl rubber, and metal foil offer opportunities for building

low-cost rainfall catchments, but they are easily damaged by wind. Plastic films covered with gravel (FIGURE 9) have proved more successful; the gravel protects the underlying membrane against radiation and wind damage. These catchments, if properly constructed and maintained, can be durable, with a projected life of more than 20 years. They are useful where gravel is readily available and maximum runoff is not required, (gravel retains some of the *water). ,’

General Principles

Water-harvesting me must know:

. the soil (espec erodability);

thods are site specific. Before a system is installed, one

:ially characteristics of water-holding, runoff, and

. the”topography (slope and the direction followed by natural runoff);

. , the precipitation characteristics (amount, reliability, etc.); and

. the climate (wind, sunlight, temperature, etc.). Because rainfall in arid lands is intermittent, storage must usually be an

integral part of any rainwater-harv?%ting system. However, when water- harvesting techniques are used for runoff farming (chapter 2), the water is

.,.’ “stored” in the cultivated soil itself. Sometimes it is possible to build catchments to feed existing-even ancient-water-storage structures (FIGURE 2).

5

Advantages

Surprisingly, the livestock-carrying capacity of many arid rangelands is limited more by a lack of ‘drinking water than by a lack of feed. Rainwater

3Fink, et aL.1973. (2ee Selected Readings.)’

16 MORE U’ATI1R I:OR ARID LANDS

I:ICURE 8 Paraffin wax is shredded and spread for rainwater harvesting in Arizona, USA. Mt$ted by the sun. the IVX\ flows into and seals soil .porcs. making a ~~~~t~~r-r~‘pclIc~~ t wrl‘:lcc that 5hcd\ \\2tcr cf‘t‘iclently. (1i.S. I)cpartnlcnt of Agriculture)

‘RAINWATER HARVESTING !

17

FIGURE 9 Laying polyethylene sheet for a rainwater=catchment in the Sonofan Desert, Arizona, USA. Sheet was later covered with gravel for protection against

( damage antI sunlight. (C.B. Clilff)

harvesting may’ be the only source of extra water. Improving drinking-water supplies ‘on arid rangelands or other remote watershed areas increases the value of these grazing lands and allows Jhe available feed to be used more fully ./

A water-harvesting system, once installed, will provide water without requiring fuel or power.

*Recently, catchmerit c<nstruction costs have fallen sharply, and further cost reductions seem possible. The more promising chemical treatments and soil covers (such as wax, reinforced-asphalt membranes, and gravelled plastic) provide sediment-free, high-cluality water for less than U.S.SO.05 per m3 in a 300~mm rainfall zone in the southtiestern United States.4 Under fav;,r- able conditions the l%nd alteration methods are the least expensive of a11 and could provide water suitable for most agricultural purposes at much lower cost.

Arid developing countries ‘that produce and refine crude oil could use’ asphalt ,to construct water-harvesting catchments. Heavy petroleum fractions such as asphalt have limited demand and are often persistent pollutants, difficult to dispose of.

4CIuff, et al. 1972. (See Selected Readings.)

18 * . ‘,\ MORE WATER FOR ARID LANDS

. Limitations ‘,

Because raidwater harvesting depends on natural 9 rainfall 1) it is no more ! lil reliable* than the we&her. Without adequate storage, the system will fail in

drought years. In locations with an average annual rainfall of less than 50 to 80 mm, ra@water’harvesting will probably never be economically feasible.

In applying w$er-harvesting methods to a given area, care is needed to minimize side effekts. Poorly desjgned and nianaged rainwater harvesting can lead to soil erosion;, soil instability, and local floods. Soil erosion, a constant . concern, can be co~~trolled if the slope is short and not too ,&eep (and if

:&ains are suitably iloped). Slope also affects the quantity and quality of ‘p-unoff. The fiost’eff!vient water harvest is from small. gently sloping (prefer- ably 1 to 5 percent)‘c&chr&nts.

Today, little expei,tise is available for designing rainwater-harvesting s&ems. Furthermore, ib many arid areas data are lacking on rainfall intensity L and variability.

A rainwater-harvestin 8 catchment must withstand weathering and occa- sion$l foot traffic. Fen$ing may sometimes be reqgired. Environmental cont&lination must be c&stantly considered, Colored or contaminated runoff wbter will require treatment before it can be used for human consumption. (p simple system that uses a sand filter is shown iq FIGURES 10 and 11.)

Mos$\ soil treatments (especially the cheaper ones) have a limited lifetime and musk be renewed periodiaally,-l They also require occasional maintenance because qf cracking caused by unstable up thro&& the ground cover or trea cd soil. No one material has proved

fldation, and plants growing

superior ft; all catchment sites. 6 \

\ 9 L

Stacje of D&lo pmen t

I\

1 D

Rainfall h&vesting is almost 4,000 years old: it began in the Bronze Age,

c . when desert dtiellkrs smoothed hillsides to increase rainwater runoff and built ditches to colle\t the water and convey it to lower lying fields (FIGURES 2 --

. 4). This practicd permitted agricultural civilizations to develop in regions with an average rainf$ of about 100 mm, an inadequate rainfall for conventional modern agridultuhe.. 4

In modern times, but before 1950, only a few Frtificial catchments were I built, mainly by government agencies to collect water for livestock and wild-

life on islands with high rainfall and porous soils (the Caribbean island of Antigua, for example’). The cost was usually high. In the 1950s interest in

‘Batemy, 1971. p. 11 (See P. 5.1 1

RAINWATk I-IAK\‘I~:STING 19

~‘lllrcllIly. lall~\v;llcl~ Iwcsllll~ I\ 1‘01. s~nall-~c~~l~ use. t‘or l‘;lrm>. v1ll2ges, a11tl I~vc:st~~l~. ‘1’1;~ la~ld-altc~-atiol~ method I:, I-cady 1.01 ~rnnl~cil~tc worldwide use. Au~tt;111a and Israel use it already; in the Sudan and Botswan;I (FIGliKE I’) LZ;I~C~~IHCII~ tn~,~l\s laavc l~ccn Intr~~duced III tcchn~cal ;1ss:1s~;lrlc‘c programs:

(‘hcrnical tl-catmcn$s and ground c‘<)vcrs. though still mainly esperlmental, arc used on ;I worldwide, but slight. scale. Proved to be technically feasible and successt‘ul, tlley are not yet economically attractive enough to generate widespread adoption. .

Needed Research and Development

No n~ctl~od 01’ raiilwatot- ha!vcst~ng 11~1s hccrl sublccted to ;I long-term cconolnic: :111alyl;15. Large licld trials III dll‘l‘crcnt areas arc nccdcd to build up ;L data base that could lead to ;I bcttcr understanding 01‘ tile cco~~o~n~c viability 01‘ dit‘l‘crcllt 111ctl1ods III dif‘t‘crcnt economic cnvirunmcn~s. Developing countries particuI:lrly need the data. because most of the technology was _ designed for Ismel, Australia. or the United States. With adaptive research to fit the needs, economics, and materials of developing countriG’s, rainwater- harvesting methods may be of exceptional and immediate value.

s 6Carder. 1970. (See Selected Readings.) 7Kellsall. 1962. (See Selected Relidings.)

20 MORE WATER FOR ARID LANDS Q

\.

FIGURE 11 Capping 2-m-tall internal water-storage cells with soil-cement-filled sausages (I:IGURI< 12 ). The area will nest be back-filled with sand. This technology re- quircs only a spade. Funnel. carving knife, and mallet. Kordofan Province. ‘Sudan. (M. G. lonides)

.

FIGURE 12 Catchment tank at Palapye Central School, Botswana, paved with mud and flat stones and sealed with a plastic liner. Revetment is made of ’ “sausages”- thin-plastic tubes filled with soil-cement. Tubes are sealed at one end,&d soil containing a small amount of cement is poured in. Tubes are then pricked with nails and placed m a shallow pan of water. Before the cement sets the tubes are stacked in place. No formwork is needed; the soil-cement is self-curing. (See also chapter 9.) The sausages are a modem, cheap, do-it-yourself technology. Water-storage tanks or cisterns with a catchment alongside to run the rainfall in are ancient devices, often forgotten today. (Intermediate Technology Development Group)

-7 RAINWATER HARVESTlNG - 21

The major technical-research need is to reduce the costs of sealing catchment soils and to make the treatment practical for a wider variety of sQls and situations. Industry is con.tinually form@ting new materials which should be continually monito,red ?-od evaluateq foPuse in rainwater harvesting.

Selected Readings

(See also Selected Readings, chapter 2.) Carder, D. J., and G. W. Spencer. 1971. Water Conservatiorl Handbook. Soil Conserva-

tion Service, Department of Agriculture (Jarrah Road, South Perth, Western Australia 6 15 1, Australia).

Chinn. S. S. W. 1965. Water Suppl~v Potential j?om an Asphalt-lined Catchmeut near Holualoa, Mona, HaM*aii. Geological Survey Water Supply Paper 1809-P. U.S. Govern- ment Printing Office;Washington, D.C., .USA. .

Cluff, C. B. 197 1. Plastic catchments for economical ha&estih/g of rainfall. In Proceed. in& ofthe Tenth Natiorial Agricultural Plastics Conference, ed., J. W. Courter. (Avail- able from J. W. Courter, National Agticulture Plastics Association, Dixon.Springs Agriculture Center, Simpson, I@ois 62985, USA.) pp. 192-202.

Cluff, C. B. 1974. Plastic reinforced asphalt membranes for precipitation harvesting and seepage control. In P;oceedings of the Eleventh National Agricultural Plastics Confer- ence, ed., J. W. Courter. (In press,) (Available from J. W. Courter; see Cluff, 1971:)

Cluff, C. B.; G. R. putt; P. R. Ogden; and J. K. Kuykendall. 1972. DeIlclopr?zerzf of Economic Water H&vesting Systems for Increasing Water Supply, Phase If. Office of Water Resources Research Project No. B-015-ARIZ. (Avajlable as Report No. PB-214 128, National Technical Information Service, U.S. Department of Commerce, Spring- field, Virginia 22151, USA. US$4.50.) ’

Department of Agriculture of Western Australia. 1950. Rodded Catcfzments for Farm Supplies. Bulletin No. 2393. (Perth, Western Australia.)

Evenari, M.; L. Shanan; and N. Tadmor. 1971. The Negev: Tfle Cflallerlge of a Desert. Harvard University Press, Cambridge, Massachusetts 02138, USA.

3 Fink, D. W.; K. R. Cooley; and G. W. Frasier. 1923. Was treqated soils for harvesting water. Journal of Range Management 26: 396-8.

Frasier, G. W.; L. E. Myers; and J. R. Griggs. 1970. Installation o>Asphalt-Fiberglass Linings for Reservoirs arid Catchments. U.S. Water Conservation Laboratory. Report No. 8 (Agricultural Research Service, U.S. Department of Agriculture, Phoenix, Arizona 85040, USA).

Intermediate Technology Debelopment Group, Ltd. 1969. Tfle Introduction of Rain- water Catchment Tanks and Micro-irrigation to Botswana. [Parnell House, 25 Wilton Ro-ad, London SWIV -lJS, England.) 74 p. \ ,

. Jefferson, J. H. K. 1953. A Note Based on Field Experience in Planning Hajir Excavation

OProgrammes. Memoirs of Field Division No. 4, Agricultural Publication Committee (Ministry of Agriculture, Khartoum, Sudan). ,

Kellsall, K. J. 1962. Corutruction of Bituminous Surfaces for Water Supply Catcflment ,Areas in Western Austrulia. Hydraulic Engine&s Branch, Public Works Department (State Government of Western Australia, Perth, Western Australia.) (Mimeographed notes for field staff.)

Kenyon, A. S. 1929.. The ironclad or artificial catchment. Jourrzal of the Department of Agriculttire of Victoria 27:86-g 1.

Myers, L. E., and G. W. Frasier. 1969. Creating hydrophobic sbil for water harvesting. Jgurnal of the Irrigation and Drainage Division, Proceedings of tfle American Society of Civil Engineers 95, Number IRI : 43-54.

Myers, L. E.; G. W. Frasier; and J. R. Griggs. 1967. Sprayed asphalt pavements for water harvesting. Journal of’ tfTe Irrigation arzd drainage Division, Proceedings of the Ante&an Society of Civil Engineers 93, Number IR3:79-97.

22 MORE WATER FOR ARID LANDS ,,

Robertson, A. C. 1950. Tile Hafir: IlJfzat- Wfzy- W/we -How. Bulletin No. 1. Agricul- tural Publication Committee (Ministry of Agriculture, Khartoum, Sudan).

Tadmor, N. H., and L. Shanan. 1969. Runoff inducement in an arid region by removal of vegetation. Soil Science Society of America Proceedings 33 :790-94.

Velasco Molina, H. A., and 0. Aguirre Luna. 1972. Una estimation de1 costo de captar y c almacenar agua de lluvia en regiones desertic‘as y semi-deserticas de1 norte de Mexico. (An estimation of the cost of catching and storing of rainwater in arid and semiarid regions of North Mexico.) Agrononzia, Mexico 145:74-g. j

Contacts

(See also Contacts, chapter 2.) Animal Husbandry Farms, University of Sydney, Camden, New South Wales, 2570,

Australia (H. J, Geddes) Botany Department, Hebrew University of Jerusalem, Jerusalem, Israel (M. Evenari, L.

Shanan) Departamento de Suelos e Ingenieria igronoma, Instituto Tecnologico .de Estudios

Superiores, Monterrey, Mexico Department of Soil and Water Science, Faculty of Agriculture, Hebrew University of

Jerusalem, Rehovoth, Israel (D. Hillel) District Soil ConservatPonist, Weitern Soil Conservation District, Soil Conservation

Service of New South Wales, P.O. Box 118, Condobolin, N.S.W. 2877 , Australia , Doxiadis Ionides Associates of London, O&ham Mill, Ripley, Surrey, U. K.

Hydraulic Engineers Branch, State Public Works Department, Perth, Western Australia Irrigation and Water Supply Commission, P.O. Box 74, North Quay, Brisbane, Queens-

land 4000, Australia (A. M. Carmichael) P * Ministry of Agriculture, Khartoum, Sudan *

- Northam District Office, Department of Agriculture of Western Australia, Northam, Western Australia (D. J. Carder)

.-

Soils Division,, Department of Agriculture of Western Australia, Jarrah Road, ,So&h Perth 6 15 1, Australia (I. A, F. L&g)

Soil Conservation Service 01 New South Wales, Flotta Lauro Building, 18-24 Pitt Street, Sydney, N.S.W. 2001., Australia (J. C. Newman)

University of Western Australia, Department of Civil Engineering, Nedlands, Western Australia (M. Hollick) ._

U.S. Department of Agriculture, Agricultural Research Service, Berkeley, California 94705, USA (L. E. . Myers) .

U.S. Water Conservation Laboratory, Phoenix, Arizona 85040, USA (K. Cooley, G. Frasier) *-

-b Water Resqurces Research Center, University of Arizona, Tucson, Arizona 85721, USA

(C. B. Cluff) -e . .i,_- w -

-.5! i’ Runoff Agriculture 8

F

Once rainwater runoff has been harvested from slopes (se.c chapter l), it can be used for crop production (FIGURES 13 and 14). The combination is known as runoff agriculture. ‘FIGURES 15-24 show ingenious, simple runoff agriculture systems in various parts of the world..

Runoff agriculture was developed almost 4,000 years ago to permit crop production on lands receiving as little as 100 mm average annual rainfall. Extensive investigations reveal that ancient farmers in the Middle East cleared hillsides to increase runoff water and built rock walls along the contours to collect it and ditches to convey it to lower lying fields (FIGURES 2-4). These systems allowed agricultural civilizations to survive in desert regions that today support only a small human population and product few crops. s

* Warfare and political upheavals resulted in mismanagement and neglect of the ancient. farms, but ) ,,-e techniques of runoff agriculture are still applicable

9 today= Runoff farms,‘using modern technology and crop varieties selected for local conditions (chapter 14), could benefit many desert regions. Artichokes, asparagus, flower bulbs, some fruits and nuts, barley, sorghum, pearl millet, and forages all are potentially inrsortant crops for runoff_agijcuIture; most@ are now grown in large runoff-agriculture field trials in the Hegev Desert. PI

u C.. \ ,

Methods i. *

In runoff agriculture the principles and practices depend on rainwater h&-vesting‘(described in chapter 1). The basic nee$ is a rainwater catchment that provides enough water to mature tlie crop. Obviously, the crop’s own water requirements (chapter 14) and general water conservation techniques (chapters 7- 16) are crucial to a successful harvest. Poor crop yields in drought’years are usually offset by. production in good years. ”

The type of farming practiced must make the best use of’the water. In general, perennial crops with deep root systems adapt better to runoff agriculture, because they can use runoff water stored deep in the soil, safe

23

‘4 MORE WATER I.‘OR ARID LANDS

FIGURE 13 A good barley crop produced by runoff agriculture in the Negev Desert. (I,. Evcnari)

”

fl-um.cvaporation. Some deep-rooted, drought-resistant fruit trees can be very s~&cssI‘ul. Slwrtcr lived crops can also bc grown; grains, such as pearl milletqz that ~naturc rupidly and rcquirc only one ruinktil hold particular prqnlisc.8 Plants that become dormant during dry periods and begin growing when w:ltcr becomes available are particularly suited to runoff agriculture.

The desert soils and climate of the Negcv have been found suitable for a variety 01‘ crops under rL!,noff agriculture. Excellent yields IKWC been obtained from pasture plants: field crops, and orchards,-well above those of drvland farming and comparable to yields in irrigated farming (TABLE 1).

5 companion report on’ tropical plants, now in fireparation, describes some lesser known pains that can be grown to maturity wilth a single flood irrigation. (See BOSTID

I . pllbllcatlon 16, $. 153.)

D

FIGURE 15 Reconstructed ancient farm at ,Avdat in the Negev. Farm is, and was, watered by runoff from surrounding slopes and wadis. In the foreground are four reconstructed terraces; in the background, four reconstructed channels lead runoff to the farm. To the right are traces of three channels that once carried runoff water to the lower terraces. Ratio of catchment to cultivated area is 20: 1 -each ha of cultivated land receives runoff from 20 ha of slopes, as well as direct rainfall. Cultivated area receives water roughly equal to a rainfall of 3PO-500 mm from actual rainfall of 100 mm. (L. Evenari)

be collected in easily constructed channels on the hillsides and were small enough to prevent uncontrollable amounts of water (FIGURE 1). Channels directed the water to cultivated fields which were terraced and had stone spillways so that surplus water in one field could be led to lower ones. Farmers dammed the small channels between the catchment and the fields with rocks; by removing strategic rocks from the channel walls they could guide the water to different fields at will.

A form of runoff farming that utilizes water from small,.deliberately built catchments has been practiced in Botswana.’ The water is used on school vegetable gardens.. The catchments have included school playgrounds, roads, etc. (FIGURE 12):

91ntermediate Technology Development Group, Ltd. 1969. p. 70 (See p. 21.)

3

. RUNOFF AGRICULTURE= ’ I 27 I

FIGURE 16 Orchard in Negev. Rainwater falls on the slope behind and runs down to strategically located ditches that convey it to the trees. In temperate regions agriculture is based on direct precipitation anqon practices, such as plowing, that encourage rain to infiltrate the soil, Runoff agriculture is an indirect method suited to arid lands; it collects rain from a larger area and concentrates it on a smaller, cultivated area. (L. Evenari) ‘:

r / /’ / ,, . --

, : $. :i+ FIGURE 17 Sketch of water-spreading dikes built in Pakistan, Zigzag pattern sk,ws the torrent of floodwater and allows it to penetrate the soil. Crops are thin planted in the-- ,” : wetted areas behind the dikes. (Adapted from French and Hussain. I964.{See Sele,&J$l Readings) - . b.- -

,.= ..~ ,u/, $p$ L - -:+ - L Y.

. 28 L MORE WATER FOR ARID LANDS

Water-Spreading

In arid areas the limited rainfall usually falls during short, intense storms. The water swiftly drains away into gullies, and then flows, sometimes for< many miles, toward the sea or an inland lake. Water is lost to the region, and floods caused by this sudden runoff can be devastating, often to areas otherwise untouched by the storm.

-e

Water-spreading is a simple irrigation method for use in such situations: floodwaters are depberately diverted from their natur-courses and spread over adjacent flobdplains (FIGURE 17) or detained on valley floors (FIGURES 1’8 and 19). The water is diverted or retarded by ditches, dikes, small ‘dams, or brush fences. The wet floodplains or va@y -floors can then be

4 used to grow crops. Water-spreading is also frequently wcticed on range and pasture lands. >P

Water-spreading systems need a careful design and ngineering layout to i withstand floodwaters. Potential sites are found on many arid and semiarid ranges, sometimes (as in the rainshadow of a mountain range) where floods are more common than rain. They must be selected with full consideration for topography, soil type, and vegetation. Two requirements are essential:

0 Runoff waters, available for spreading, produced by an upstream drain- z age area that gives at least a few water flows each year; and

FIGUR; 18 Man-made .terraces (reinforced by unpalatable bushes) built in ancient times to slow down and capture floodwaters in this wadi in the Negev. Built thousands

-.:%f years ago, some are still used for farming by Bedouins. Terrace walls are lo-50 m -z apart and about 30 cm high. Rain brings wild flooding; surplus water pours over the

terraces; but the walls retain a pool of water that slowly sinks into the soil. Experiments here have shown that these walls are high enough to fully moisten enough soil to get crops -such as barley or wheat to maturity. Water spreading may predate irrigation. Ancient farmers built many such systems throughout the Middle East, South Arabia, and North Africa. (L. Evenari)

I RUNOFF AGRICULTURE

-.

29

0 iFloodplains or gently sloping are rere the soils are suitable for crop production. 1

Inherently more risky than standard igation, the system depends on fairly regular rainfall and 04 soils (e.g., 1 ) that facilitate runoff. A constant concern is that sediment and gravel ca ed by floodwaters may adverse- ly affect the crop land.

Microcatchment Farming

A plant can grow in a region with too little rainfall for its survival if a rainwater-catchment basin is built around it, forcing rainfall from a larger than normal area to irrigate the plant. This practice is called microcatchment farming. The previously described principles apply to this microscale runoff agriculture; many of the same soil treatments mentioned in chapter 1 can be used. s

FIGURE 19 In 1972 near the small town of Tchirozerine (close to Agades), Niger, West Africa, Touareg nomads build a rock wall to capture flood waters. The soils here absorb little moisture, and the rainfall runs away in flash floods. Using stones gathered from the fields, Touareg workers built eight l-m-high walls across the plains so that rain is retained, and absorbed by the soil. When summer showers fell in 1973, the water retained by stone dams and walls flooded nearly 1 square mile on the plain and grass flourished-extraordinary events in that area. (Oxfam-America)

P 3o ti 1 MORE WATER FOR ;RID LANDS

a

I b -

*FIGURE 20 Plan an$ cross-section of a microcatchment. Arrows indicate direction of runoff flow. Cultivated plot (c-d) is placed at th? lowest point of the natural terrain within the catch@nt; its position varies. Walls arc 15-20 cm high; c&d is about 40 cm below the,,catchmeat, holding seeping water close to the plant; root-zone soil must be at least 1.5 m deep; the a-b distance can be less than 5 m or more than 30 m, depending on climate and crop. (M. Evenari)

hkrocatcl~ents used in the Negev Desert range from 16 m2 to 1,000 m2. Each is surrounded by a dirt wall 15-20 cm high (FIGURES 20-23). At the lowest point within each microcatchment a basin is dug about 40 cm deep and a tree planted in it. The basin stores the runoff from the microcatchment. The size of the basin is matched to the water harvest expected.

The basigs are fertilized with manure, and, unlike the catchment area, their soil surface is kept loose td encourage water penetration. A mulch may also be useh to decrease’water evaporation from the soil (see chapter 9).

On an otherwise barren desert lplain microcatchments provide enough

additional water to ensure the growth of fruit trees and forage plants. Micro- catchments and variations of this method are u<ed in Tunisia for growing olives-and apparently have been since ancient times.

In the .Negev microcatchment,construction costs are .very low-from US$5 to US$29 per ha, depending on the cstchnrent size. The cash return from crops repays their construction costs within a few years.’ ’

Microcatchments are more efficient than large-scale water-harvesting schemes (chapter 1) because conveyance losses are minimized. In light rains,

’ ‘Evenari, Shanan, and Tadmor. 197 1, (See p, 2 1.)

.

RUNOFF AGRICULTURE.. : 31

”

FIGURE 2 I Microcatchrncnt farmmg in the Ncgcv. P~~mcgr;lnatc trws gro\!’ 111 5U0-1n’ rnicrocatch*nents .in a 1 00-m-rainfall rcglon. Th! onl~f sull Lrc;itrncnt 1s shaping. Tllc orchard is less dense than thyse in temperate climates. JO-60 pnmcgran;lte trees- per ha are planted. Smaller trees, such as gfapevines, can use smaller satchments (SO-100 per ha); catchmcnts of just over 30 rn’ (320 per ha) are enough to grow a srllrbush plant and guaranfee a supply of forage even in severe droughr. (L. Evenarl)

they provi& runoff water when others will not. It is muc’h chcapcr to convert a certain arca into~microcatchmcnts than to construct ;i runoff farm twausc microcatchmenls do not need channels, conduits. tcrrkcs, and tcrract w~~lls. Also, microc;ltchments can bc built on almost any slope+ including almost- level plains, enabling the farmer to use large, tlat areas unsuited for ruilol‘l‘ farms.

Desert Strip (or:Contour Ca$hment) Farming

Des&t strip, or contour catchInent’;:,farInin g is a modification of microcatchment farming. It employs a series of terraces that shed water- onto a neighboring strip of productive soil. They are often. tiered up a hillslope

i

* h 37 1ORl \\.A11 I< I OR :1Rll) LXNl)S

(1:IGURli 24),but on lcvcl terrain SllllJC I‘01 lllC i3litllllCllt i;lll bC

made by nlounding soil between the The catchment section ca atural state or cleared of rocks and

vegetation, planted with range gr s, or made irnpervlous by the sealants described in chapter ~1. Desert stri are, in general. even t’asxr to install and maintain than rnicrocatchme ads are bemg tested in Arizona; in Wadi Mashash, Israel, it is used to duct gra/.ing for sheep (FIGURE 14).

Advantages I

FIGURE 22 Microcatchmemts in Botswana with Z-year-old apricot trees. (U. Nessler)

RI!NOI:I AGRl(‘ULTURl~ 3 3

FIGURE 24 D,cscrt s JJ runoff farmin, \ry. ~7 at Pace Esperimrntal Ranch near Tucson. Arizona, USA. Grapes are’ cultivated in draina:: xvays. Gtchment Jrea treated \vlth sodium chloride remains bare: untreated foreground area has returned to native grasses. Bottom left-hand corner sho\vs part of an expanded-pol!,st).rene floating cw’er designed to reduce evaporation from the pond (see chapter 7). (C. B. Cluft]

34 , MORE WATER FOR ARID LANDS

Wales, Australiti,‘ from 1968 to 1973 was 2.66 sheep per ha. Without water- spreading the carrying capacity of this region is 0.18 sh%ep ‘per ha (as measured over the 25 years, 1947- 1972). Seasonal feed shortages still occur in poor rainfall years at Conneybar, but their consequences are much less than they would have been,“,without water-spreading. High grazing intensities have -been ap&ed for short @riqds. Up to 586 sheep per ha ha& been grazed on’ a 28 ha pa’sture for periods of up to 4 days. Runoff-irrigated fieldsare, used 2s special’fields to increase control over, and mininiize losses of, newly born animals and to hold stock during shearing, dippicg, mating, etc.’ 1

Runoff agriculture can extend the season during which forage is succulent .,a _-and-nswrishing,-providing.gre.en.forage whenit is especially ne-eded.. .~ _ ,

’ . Water-spreading can provide erosion control, fijr it deflects the torrent of water and- dissipates its energy. . . i . -

7 -

Limitations1

ulture requires a deep soil that can store water between rains. r deeprooted crops, such as trees &d shrubs, which can tap

stored water and depend less on frequent $infall. Annual crops, in contrast, need rain at the beginning of the growing’$eason and sometimes at intervals ’ , ._ thereafter. .i:

The method is enhanced.by plant varieties able to withstand intermittently wet and dry soil. As in normal agriculture, yjelds also depend on insect and disease control.

Environmental pierequisites are l A minimum mean precipitation of 80 mm pe! r&y season if the

rainy season coincides with the cold peripd of the year, more thq 80 mm if it occurs during sumrrier when evaporation is greater;

l Crust-forming or impermeable !oils on the catchment areas; Soils in the cultivated areas with high water-storing capacity; .

l

. Not more than-2-3 percefit salinity inThe cultivated soil; and l A minimum of 1 S-2 “m of soil depth in the cultivated area (unless

water-storage facilities are available). In runoff agriculture the water must be distribuied evenly ‘over the

cultivated area to prevent ‘prolonged ponding, overirrigation, or deep percolation losses., In some cases the area to be cultivated can be constructed so that any excess spius to a lower collection leve!. The cultivated area must be uniform, without gullies or ridges. Before deciding oh runoff agriculture, one needs to consider

l The.wtiter-use characteristics of plant;to be grown;

’ lCunnin&mn. 1973. (See Selected Readings:) ‘.

.

? RUNOFF AGRICULTURE 35 - c

. Their yields; 0 Their ability to resist drought; --- e Whether the soils in the cultivated areas can store enough water to

mature the crop; and 0 The amount of evaporation from the soil surfacg

Stage of Development

In ancient times runoff agriculture was widespread over the whole arid region of the Middle East, southern Arabia, and North Africa. On many thousands of hectares of the Negev Desert, it was tlie basis for civilization (FIGURE 4).

Runoff agriculture has been shown to be technically sound, for modern use, too. Its rebirth as a systematic method took place in the Negev Desert in Israel, where large-scale experiments have been conducted for the past 15 years (FIGURES 15, 16, and 2 1) and a training school for developing-country personnel is located at Wadi Mashash (FIGURE 23). Some microcatchment ‘ farming occurs today in several other arid countries such as Mexico, Botswana (FIGURE 22), IiClia, Pa&istan, and Australia. The microcatchment method is used to grow wheat and fruitatrees over a 70,0dO-ha area in Khost province, A,fghanistan. j

. Needed Research and development D

Runoff agriculture can be used today if care is taken in selecting the site, designing the system, and selecting the crop. With good management it can make arid wasteland productive and can be an economically sound investment.. Modern -experience, however, is limited to a few isolated projects. Intensive technoeconomic evaluations in several regions of the world with different +mates, soils, and crops are needed to identify its potential for the future. .

To make runoff agriculture more effective, there is a need to develop crops better suited to it (further discussed in chapter 10). For example, if crops matured in 60 instead of 80 da s the soil would not have to store so much Y! ’ water, the risk of crop failure would be lessened, the system would require less rainfall, and management requirements would be reduced.’

In rnicrocatchment farming the crucia problem is still the optimal size of the - -4 * i microcatchment for each species. It is obvious that this parameter is relative

not only toleach species but also to precipitation,-soil qua-lity, and steepness of gradient. ,We have much to learn about such matters. Other problems concern optimal depth and the size of the basin in relation to the size of the ”

A

P. Pa

36 MORE \VATI<R I.OR ARID LANDS

catchment area. These factors are most important because they determine,. intor alia, the size of the surface area wetted by the flood and the volume and depth of the water column in the soil. These in turn affect the time during which the soil containing the root system is waterlogged and soil and root aeration is bad. A knowledge of these factors may even lead to different patterns of constructing the basins and the placing OT the trees-perhaps on a knoll inside of the basin. There may also be the possibility of increasing runoff volume by pretreating ,the soil surface of the microcatchments in different ways. l2

Tcchnoeconomic studies arc particularly needed for runol‘l‘ agriculture using chemically treated and ground-covered catchments.

Selected Readings

(See also Selected Readings, chapter 1.) Cull. J. K, 1964. Water spreading at’ Lanherne. Qlr~~o~slar~d Agricult7rral Jourt7ol

n 90:389a-93. Cunningham, G. M. 1970. Waterponding on scalds. ./orrrt7al ot f17c Soil C‘onscr7lariot7

Srnlicc of Nell South I\Jules. X:146-7 1. Cunningham, G. M. 1973. Itlutcrsprc,oditz,~ atrd tt~uterpotdit~,~ ot1 .4usm/iatr Kat~,yelatds.

Paper prcscntcd at the Alice Springs Symposium on \\‘atrr in Ran~elunds, October . 1973. (Available frvrn the author; SW Contacts.)

I;vcnari, M., ct al. 1968. Runoff farming in the dcscrt. 1. I’.\peruncntal layout. .Qrotl- or)~l’ .Jorrrt7al 60:29-32. (SW also Shanan, ct al.; Tndmor, et al. belo\r.)

French. N., and I. tlussain. 1964. Wulcr Sprca~i,q .4fat77~al. Range %lanagcment Record Nunlbcr 1, West Pakistan Range Improvement Sclwrnc. Lahorc. Pakistan.

llauscr, V. I,., et al. 1968. Conservation bench tcrraccs. 7kat7sac.bot7~ of‘ 1/7c A tt7cricot7 .(;OLie[.\. oJ. A~yricuf~ural I:‘tt~yitlcer~ 1 I : 385-98.

‘loncs, R. M. 1966. Tree t)stablishn&nt on sculds In the Hay Plain. ./oorv~a/ of 111~ Soil Cottsm*a~iorl Sm’icc uJ .Ye~v Soutlr h’ules 22 : 2-7.

Michelson. R. I-1. 1966. Level pan system for spreadin g and storing \\‘;ltc shed runoff. Soil Scicrlce Socict!’ 0J‘A r77iJrica Proceediy~s. ,30 : 188-9 2.

Newman, J. C. 1963. A’atcrsprcading on marginal arable areas. Jourt7al o rF7c Soil Cotisrrvalioti Sen’ice of’.Ve~. Soutfl Wales 19 :49-58.

;,.

Newman, J. C. 1966. Waterponding for soil conservation in ,tiid areas in Ne\v South Wales. Jorcrtml of’tfle Soil Cotxcn:aTior7 Setvice of:\‘e\I’ South Wales 22: 18-28.

Procrrdit?,qs of Clue Wa/orrr Hqnlesbtq S,\~ttlposiltttl .?6 - _‘8 Jlarr-17 19 74. P17oct7ix Ari,-otia .j 974. Published by Agricultural Research Service. (\\;hile supplies last, single copies avail~lblc l‘rcc from U.S. \VVatcr Conservation Laboratory. 433 l-l<. Broad\vay, Ph(H:nix, Arizona 85040, USA.)

Quilty, .I. A. 1972. Soik conservation structures for marginal urabk areas: diversion sprcadcr banks and tank drains. .fourtial OJ Iflc Soil C’ut7scr7~a~7otr Scrl~iw o/ Nrw Girl/r IVaics 28: 157-68.

Slx~nan, L.. ct al. 1970. Runot‘t’ 1:arming in the dcscrt. Ill. Microcatchments ivr improvc- mcnt of desert range. Agrotlottl~~, Jowtlaf 62:445-g.

Tadmor, N. H., et al. 1970. Runot‘f‘ farming in the desert. IV. Survival and yields of’ purcnnial range plants. .4,qrotzot’h~~ JourtzoI 62:695-g. 1

Tadmor, N. H., et al. 1971. $Runoff farming in the desert. V. Persistency and yields 01 annual range species. Agrotwmy Journal 63:9 l-5.

12Evenari, Shanan, and Tadmor. 1971. Op. cit. p. 228. \ Q

s ,

r F-.

RUNOFF AGRICULTURE I 37

Zing, A. W., and V. L. Hauser. 1959. Terrace benching to save potential runoff for semiarid land. 4gror1orny Joumal 5 1:289-92.

Contacts . II (See also Contacts, chapter 1) Central Arid Zone Research Institu-te, Jodhpur, India (H. S. Mann, Director)

-3 ollege of Agriculture, University -of Arizona, Tucson, Arizona 85721, USA

Q

(W. G. Matlock) partment of Agronomy and Plant Genetics, University of Arizona, Tucson, Arizona

* 85721, USA (N. F. Oebker) German Agricultural Group, P-0. Box 183, Kabul, Afghanistan Intermediate Technology Development0 Group, Ltd., Parnell House, 25 Wilton Road,

London SWlV 1JS:‘England @ Oxfam, B. P. 489, Ouagadougou, Haute Volta, Africa (M. Bchr) Soil.Conservation Service of New South Wjles, Condobolin, New South Wales 2877,

Australia (G. M:Cunningham) Wadi Mashash, a runoff-agriculture train& $&tcr in the Ncgcv Dcscrt for trainees

from arid lands all over the world (hi. Evenari, Botany Department, IHebrcw University of Jerusalem, Jerusalem, Israel). Also .contact: Wadi \iashash Information, Center, 61 Darmstadt, Paulusplatz 1, West Germany (0. Schenk and U. Nessler).

.

.

.\ ,

0

’

’ , te,r

‘1 n

,IRRIGATION WITH SALINE WATE-R .9

39 - .

proved practical for producing crops. Seawater has a total salt content of about \\35,000 mg/l: greatly exceeding the tolerance of even the most salt- toleranit crop studied ‘to date-Suwanee Bermuda grass ~r~ru~dorz dactylou, which can tolerate about 12,000 mg/l.

The type,.as well as concentrationyuf salt in the water is important. For r example, the relative concentrations of sodium to calcium and magnesium affect a water’s suitability because high sodium ratios affect soil structure (compare FIGURES 46 and 47) and plant nutrition. The anion of the salt, ” c.g. chloride or sulfate, may also be important.

In the practice of saline irrgation, the basic premise IS that proper. . irrigation and drainage management prcvcnt salts from building up in the soil. It is csscntial to avoid this buildup by Icaching: applying more irrigation water tliari ~hc^‘“p~a~L. rcquircs so that the cstru water carries the salts down -., I

FIGURE 25 Date palms ‘in Southern Tunisia that have been irrigated for 4 years with water containing 2,000 mg/l salts. The estenslte. drainage system is required to facilitiatc Icaching. (J. \V. van Hoorn) 7

1.

4oi I MORE \k’AI‘LK 1,OR ARiD LANDS ,

belk)w the plant’s roots. The suitability uf saline water for irrigation is thus also governed by the leaching chara~tekstics of the environment, i.e., whether- they facilitate or retard the reilova! of salts from the root Lone (FIGURE 2.5)‘. If the leaching characteristic’s of the soil particles or the overall drainage of the area are iqsuffkient, soil saiinity will increase, and&he final result In’& bc a barren wasteland. Light-to-medium-textured soils that arc hut subject to structural changes that restrict water tlow art” III&C likely to be successfully irrigated with saline waters.

According to rcccnt findings, new irrigation methods can incrcasc’a crop’s lulcrancc to salinity. kumparcd to furrow irrigation. trlcklc irrigation (chdptcr 1 O), I‘or ~xumple, has been shown to improw y~clcls 01‘ crops irrigated with saline water (2.000 - 7,500 i;lg/ I ). Tllc Aalt stresses on ;I plant are aggravated as the soil dries but and the XIII i~~nccn[r;ltlc)n Inc‘rcascs. Frcqucnt rrrigations (as in the trickle method) minimi/.c such strcssc‘s.

*

Sal’inc ground, surface; and cstuarinc waters ;lrc w~dcly av~~l;~hlc but rl:ot , oI‘t<n used 1‘07 irrigation; new research Ilndirlgs make ‘II poss1191c to USC them

‘nlorc widely for agriculture, kindscaping, etc. The cost 01‘ using saline water. cspcclally from aclulfcrs,ncar tllc surl‘acc. IS ^

riot likely 10 1x2 csccssive. ‘At Kibb.ut/. Mashabei S’Jcll in rhc NcgeC Desert

FIGURE 26 Irrigating c’otton with brackish water (2,500 ppm .dissolved salts) caused i stunted plant, but the cotton yield was 59 percent higher than \vith freshwater irrigation. Spraying plants with the transpiration-suppressing plant hormone ;ibsclslc acid (see chapter 13) filrther increased cotton yield. (h4. Twcrsky)

,

42 .

MORE WATER I-OR ARID LA

a (lOO-mm ‘rain) a 4,8,00 m3/day electrodialysis plant desalts underground brackish water. For comparison, water from the same wtll (2,600 mg/l) has been used to irrigate cotton (FIGURE 26), whetit, maize, sorghum (FIGURE 27), Rhbdes grass (FIGURE 28), Bqrmuda gras$, etc., and various vegetables. After 3 years, economic and general-utility considerations’favor direct u-of .the saline water over the electrodialysisithe saline aquifer is now used for’this L purpose. ’ 4 0

?f > b /’ ‘.’

Limitations .

&.

Although saline-water irrigation holds &citing possibilities for the future, it dots not promise t.he conversion of vast stretches of arid land into cultivated fields. Many crops cannot tolerate it: indiscriminate use may severely damage the soil; and suitable soil and climat: do not always coincide with suit.able water. Furthermore, the groatcr management skills necessary may not*bc available.

To irrigate with saline* water and maintairr good yields demand good water managcmcnt by trained kpccialists. The hype’ and ,nrLx of salts and their con-

ccntrations iR the water need to bc investigated before a decision is made to 3 use saline waters. Saline-water irrigation wiil incrcasc the salinity 01‘ groundwater and possibly make it unsuited for other uses.’ I( groundwutc.r j IS the wurce, t!lc project may have a short useful life. If poorly managed, irrigatyyn with saline water mhy seriously damage the soils and cvcn m&c them barren.

When irrigation water contains 5,000 nsg/l or more ut‘ salts, lhc leaching requirements for even highly tolerant crops may be substantial. For csample, more thaa 2.5 percent extra water may be needed just t.o move the salts below the root ‘zone; if,less.is.used, safination of the soil occurs because salts are not removed as fast as they are added.

Even highly tolerant crops may go througli salt-sensitive stages when they need low-salt water. For csamplc, seedlings of‘ small grains and sugar beets arc sensitive, though the adult plants arc not; saline watt‘r hiay impair their dcvclopmcn t. ‘\ I-

One must ,,bc car;ful in applying test results frum tcmpcratc regions to tropical arid lands. Tile s,ame crop grown iri temperate or humid regions can tolerate more highly saline water than it can in arid regions because rains (and soil waters) dilute the irrigation water. Lower temperature niiy also increase a plant’s sart resistance.

141nformation provided by J. Schecter, Acting Director. Research and Development Authority.

Uniwnity of thti Ncgev-

* \

e . \

A

i .

i,

. .

P

. IRRIGATION WITH SALINE WATER I 43 . ,

Stage of Development ‘, ,

L The use of highly saline water for irrigation has been fairly limited. As _ already, rrientioned, iarge:scale experiments are under way using brackish water for irrigation on sand and sandy loam soils in the Negev Desert. The u&z

I of brackish water for irrigation has been stuiring’-7 ~w%&+I-------~ rgear”cl?’ at six exp&-ime.gt”al stations iji ,Tu’nisia. Major objectives of this UNESCO-sponsored program were to determine

3 optimum use of the avail-

able saline surface and growd waters and to c trol soil salinity through improved irrigation techniques. As a result, saline river water containing 2,000 - 3,500 mg/l of salt is today used in Tunisia for irrigation on a large s%le in the Medjedah Valley (and other locations) on medium-to-heavy- textlured soils fitted with an extensive tile drainage system (FIGURES 25 and

..27>. w ,’

t

‘.

. ,, Needed Re&arch.and Development

‘1 ‘\ c Breeding and selection of plants that can us’c water of higher than normal minera! content is very much needed. The grehtest,‘success will undoubtedly be with drops already .show.ing some tolerance i to salinity, e.g., cb@tal Bermuda grass, barley, /cotton, wheat, sugjr bee’ts, .and perhaps the more salt-tolerant vegetables. Some varieties with greater salt tolerance than usual arc known and may become the basis for breeding’stock.

Using saline water for irrigation requires so$isticated managem.ent, but 1~ _. detailed management requiremtnts are not fullyi’understood and need careful ’

’ investigation. The ffllotiing r&d par)ticular attention: l ‘. <Defermining ihe relations ‘p between salihe water and the physiological

“stress .performance of plarits; .“’ /

. Alleviation of stresses by’different irrigition, fertilizatioii;oil aeration, lcaching”~ractices, nutrients, hormones, &e&al and physical treatments, etc.: and- . i:: . Q

. , Fie’ld application 0; the knowledge gaiLed. , a.

_ Selected Readings ._. “.. . . . . . . m

Arnon, I, 1972. Crop Productiart irl Dry Regi& I~olun~c I: Background and Principles. Barnes and Noble, New York and Leonard Hiil Books, London. 650 p. -

Bernstein, L. 1964. Salt~ole~ance of Ibnts. ,hgriculture Information Bulletin No. 2811, U.S. Government Printing Office, Washin$on, D.C. 20402, USA. 23 p. (USSO.20).

Casey, H. E. 1972. Salinity Problems in Arid Lands Irrigation: A Literafure Review and Selected Bibliography:,Arid Lands Resea,!ch Information Paper Number 7, University of Arizona, Office of Arid Lands Studiesi Tucson, &iz’ona 85721, USA. 311 p.

FAO. 1971. Sal@ity Sehzar Baghdud. Irrigation and Drainage Paper Number 7. Rome. 254 p. ‘.

b

Levitt. .I. 1972. Resportscs of Platrts to l:‘t~viroth~cl~tal Stresses. Academic Press, Ne\r York. =

Stylianou, Y., and P. I. Orphanos. 1970. Irrigatiott of‘ Shartmutl oranges \csith saline lrlatcr. Technical Bulletin Number 6. Cyprus Agricultural Research Institute, Nicosia, Cyprus.

Twcrsky, M. 1971. Factors of Chemical Fertilizatiott it1 Saiitle IVarrr lrtfyatiotz .A fir~Ilic~\t~. The Negev Institute for Arid Zone Research, Beer Shew. Israel.

Twcrsky, M., and D. Pastcrnak. 1972. C’rop Irri~~atiott \ilitlt Brackrslt It’atcr lit .Ilas/tahl~, SatlcII. Preliminary Report, The Nc,g~v Institute fur Arid Zone Rcs?~r~h, ,Hccr Shcv;r. Ismcl.

I~NlfX’O. 1972. llydrolo~yi~al Aspcvcts oj Salitrc IVatcr Rcsoiirtc~s .4 Prol~tsiottal A trtlotatctl B~!dio~~aphy. Distribution No. SC/WS/438. Pans. 66 p.

IlNI~X’O/I~AO. 1973. Irri,yotiott, Draittap ad Salrttit~. .4 tt /t7t~~rtiatic~t~al Swrw Hook. Ilutchinson. 5 10 p. (Available i’rom Unipub, Hex 433. New Yclrk, NC\{ Yurk 100 16, USA.)

LJNI.SC’O. 1970. Reclwrcltc ct ltirttlatrott ctt ttraticrc d ‘irri,yaa[rott al’(‘(’ tfps ca1t.v salws (‘tt Tlrtrisie. I’aris. August 1970.

van Schill‘gxlrde, J., et al. 1974. Irrigation management for salt control. Jourttal of‘ t/1(, Irtigatiott attd Draittage Dilisiotl Froccdittgs 61’ the .A ttlcricat7 Society* oj Cillil I:‘ti~itiect-s. (In press.)

Waiscl, Y. 1972. f3iolo,q\j of Ilalop/t~:tcs. Acudcmic Press. New York. 395 p.

Contacts *

(‘cntr:ll S;~lt and Mx-ine (‘hcmicals Rescgch lnstitutc, Bh;Lvn;Lg;Ir. GuJx;lt. IndiG Ccntr;ll Soil Salinity Research Instltutc, Kamal, Punjab, India . (‘cntrc tic licchcrchcs pour I’lrtiliwtiun dc I’I;au S;llcc cn Irrlgatlon, lioutc dc Soukru,

13. I’. IO. Ariana. I’unisia Agricullurnl University, Dc Nicu\\rlanden, Nicu\vc K\;3na;11 Il. \\‘agcnmgen. The Nethcr-

lancls (J. W. wn IIoorn) Kibbut;l Rovivim, Negev. Isruel (J. dc hlalach) Ministry 01 Agriculture and Natural Resources. lilicosia, Cyprur Ncgcv Institute for Arid Zone Research, Beer Sheva. Israel (J. Schccter) U.S. Salinity Laboratory, U.S. Department of Agriculture, Agricultural Research Service,

,. .’ P.O. Box 672, Riverside, California 92502, USA (J. van Schilfgxude, Director) Water Resources and Development Service, Land and \\‘ater Development Division, Food

and Agriculture Organization of the United Natiq,ns, Via d.r,lle Terme di Caracalla, 00 100 Rome, Italy. *-

II

2

4 Reusing Water

Reusing water can greatly lower the overall demand for water resources. Wastewater can be used for irrigation, for industry, for recharge of groundwater; in special cases, properly treated wastewater has been used for munic-

7 ipal supply, With careful planning, various industrial and agricultural demands may be met by purified wastewater, thereby freeing freshwater for municipalities, which require better water, suitable for human consumption.

Water reuse may have greater impact on thature usable water supply in . arid areas than any of the other technologies discussed in this ieport.

Methods

Agricultural Use ,‘“’

Spreading wastewater on marginal land to create new farmland may prove particularly important in arid countries. In such areas reclaimed water will ’ probably be used first for irrigation. Filteang wastewater through soil removes all particulate matter: most cations and some anions (including phosphates) are strongly adsorbed, and organic matter is decomposed by soil .bacteria. These actions can contribute plant nutrients to soil (FIGURES 29 . and 30). +

Using municipal wastewater for irrigation is especially attractive where agricultural lands are located close to cities, because the plant nutrients in sewage would otherwise go to waste. Some biological treatment of sewage should precede land application, but for many crops the degree of treatment required is so’low that little technology and .capital investment are requi’redl (Mexico City uses vast amounts of untreated sewage as irrigation water.) Where irrigation systems are already in use, connecting them $0 municipal systems is fairly simple, though institutional arrangements may prove difficult. The American Public Works Association has recently stated that

on the basis of the exhaustive study which was undertaken, it must be u . . coneluded that the land application of’ wastewaters offers a viable alternative ’

\

L

46 MORE WATER FOR ARID LANDS

., FIGURES 29, 30 Two maize crops on a lo-ha plot at Rhodesia’s Salisbury sewerage works, 1971-72 season. Tall maize on left was given a particularly heavy preirrigation with treated sewage. Stunted maize at right was irrigated almost entirely by rainfall. NO additional fertilizer was added to either crop. The contrast shows very cle’hrly the fertilizing effect of nutrients in the sewage. (Rhgdesia Agricultural Journal)

h

: to advanced Treatment processes and deserves serious consideration by many communities and industries throughout the United Stat&. Land needs, when taken in perspective with total land uses, are not unreasonable and may, in fact, play a desirable social role by‘ providing green belts and open areas, and

Treserving rich farm lands and cloistered areas. The conclusions of the report point to the almost unqualified success of this method of application, bothin this country and throughout the wbrld, when the facility has been properly operated and efforts have been made to apply sound engineering, geIoiogical and farming expertise to design’, construction and control procedures.

Since 1892, Melbourne, Australia, with~a present populatl,>n of almost I 2 million, has disposed of its’kastewater i

P

irrigation at the 109 km2 vBoard of Works Farm at Werribee (FIGURE 3 1) A total of 4,200 ha of the falm is employed for irrigated-pasture of which 11370 ha are used for graiing 15,000 head of cattle thrbugh the year, Forty to: fifty thousand sheep are fattened during spring and summer. Health restrictibns are imposed only on the sale of

I “American Public Wor& Association. p. viii. (Sek Selected Readings.)

REUSING WATE’R 47

FIGURE 31 This Melbourne and Metropolitan Board of Works Sewerage Farm at Werribee, Australia, has long used treated sewage from the city of Melbourne as irrigation water. This formerly barren, disposal facility,

arid, windswept plain is the major sewage- serving more than 1.5 million people. (Sewage flow averages 360

million 1 per day, 950 mld during rainy periods.) The farm grazes 15,0@ cattle a year; 40,000-50,000 sheep are fattened during the spring and summer,,regult&tg in the sale of 5,000 cattle, 36,000 sheep, and 250 bales of wool during an ave”rage”year. (Melbourne and Metropolitan Board of Works)

45 MORI- WATER I‘OR ARID LANDS

-<

c

,^ y

cattle and sheep for slaughter-but the 0.02 perc&t condemnation rate of . cattle carcasses is the same as that for the surrounding area. No higher incidence of disease among farm employees has been found to result from their employment.’ 6 In less well-op erated sewage irrigation projects in India, however, the operators have been found to have abnormally high loads of parasites. ”

Recycling ir-rigation water runoff by pumping it buck to the head of the system is another way to reuse water for agriculture. but salinzation of the soil is a serious hazard (see chapter 3). Industrial wastewater may also bc lit for irrigation, but it may require treatment when, the industrial process adds

’ chemicals det’rimental to plant growth or public health.

1

Industrial Use

Municipal wastewater from secondary treatment plants can be used for cooling, ore separation, and other purposes that do not have severe water- quality requirements. Use as process-water requires advanced treatment. The degree and kind of treatment depend on demands and economics of the application. For pulp and paper production the USC of wastcwatcr al‘tcr only limited advanced treatment has been found to be cco110m~c;111~ feasible. ” c)

Municipal Use

Municipal use places the highest demands on water quality. Wastewatcr must usually undergo secondary and tertiary treatment to make it potable. ’ Processes for removing ammonia, nitrates, and phosphates arc availublc; residual, potentially toxic compounds and dissolved organic substances can be reduced to very low’ levels by adsorp.tion on activated carbon. Dissolved mineral matter can, if necessary, be reduced‘ to acceptable levels by ion ’ exchange, electrodialysis, or reverse osmosis; however. adding these processes, can double or triple the capital and operating costs of a conventional treat-’ ment plant.

,Producing water of the necessary quality requires” a large investment in capital equipment, power, and chemicals. The cost;-()f such watcr.is rclativcly~ high, but may be lower than that of desa.ltcdfseawater (chapter 6); in arid lands its may be lower than the cost of developing alternative supplies of water, though not if treatment is needed to remove dissolved mineral salts.

Windhoek, South-West Africa, a metropolitan area of 84,000, meets its water needs by treating and recycling into the &table water supply 4 million

* 3 ’ %bid. Section V. P 171bid. p. 147. ‘%ersonal communication from National Institute for Water Research, Pretoria, South b

Africa (see Contacts). , I D‘

. .

.

REIJSING WATER 51

however, with ,thc plan,ned. Bnd deliberate reuse of water. whi’~h is increasing. . As demands for existing resources in water-scarce areas become even greater, its potential is highly encouraging. Although the technology for reuse is now available, economic considerations will probably .limit its use initially to specialized locations or purposes. Even so, such uses may release natural sources of water for potable supplies. Ultimately, as acceptance grows. widespread recycling of wastewater into the potable supply is a definite possibility. Already, sonic sanitary cnginkcrs recommend addIng properly. treakd wastcwatcr to the potable supply, bul most arc cautious bccausc of prcscnt uIlcert3iiltI‘cs over the danger from viruses :!nd hcav): metals.’ ’

Needed Research and Development D

Bccausc water reuse will undoubtedly bc highly compctitlvc !vith alter- natives, it deserves a high research/ priority. The considerable ~lount of research under way has not emphasized reusing water to increase a nation’s &pply of water as muc11 as at least 011~’ of its compcti~ors,.desalination. Rcscarcl~ should ccntor on wa’ys .to reduce cost, tu combine sccvndary and advanced trcaI.mcnt proccsscs. and to answer concerns about virologi~al hazards.

The importance of continued rcscarch to dcvclop trcatmcnts to reduce virological haLards, and rcscarch .to detcrminc the residual hazard after treat- mcnt, cannot bc ovcrs[rcsscd.

Research is nccdcd to rcducc the cost of tcrtiatjf rieatmcnts and to develop al tcrnative, less cspensive treatmcn t processes. Elcctrodialysis and c reverse osmosis show prymisc for removing many kinds of dissolved impurities, but better antifouling tec’hniques and niembranrls that require less pretreatment are needed. Improves-.~ielogical processes are needed for removitig ammonia and nitrates in secondary effluents. as are new I-ow-cost specific ion exchangers for removing mineral salts.

In the agricuIJ.Ual i\se of wnstewatcr our biggest lack of knowledge is on the effects of long-term appliuatioh. We do nol fully understand I0 what tlegrce continuous applicati&n of wast&tcr to land tlltors the nature 01‘ soil. WC dq not l@ow the capacity of soils t&j absorb different metals (boron for inst:incc) without’ permanent dnmagc. Nor have WC lcarncd h;w to prevent. or restore altered soils.

Resea_rch is also nekded to develop improved management techniques and ’ institutional arrangeme’nts whereby effluent can be substituted for potable water now used in agriculture and industry. I.

ZIAmerican Society of Civil Engineers Committee on Environmental Quality Management. 1970. (See’Selected Readings.)

.

Selected Readings b

\AgricuIture and’ Land Spreading . American Public Works Association. 1973. Sww.v of Facilities i;siq Lad ,4ppficafio,r

o/ Wastewater. Report Number EPA-430/9-73-006. Office of Wntcr Program Operations, U.S. Environmental Protection Agency. U.S. Govcrnmcnt Printing Office, Washington, D.C. 20402, USA. 377 p, (Comprchensivc supcy of 100 fncilitics worldwide where domestic or industrial wstcwatcr effluents arc npplicd to the land.) (U.S.S6.YO)

13ouwcr, I-l. 1968. Returning wastes to, the land , ;I new role for agriculture. Jrxrr,7al of

Soil utrd IlJutcr Corrscrwlidn 23 : 164-S.

Dean, II. 13. 197 I. Ultim;llc disposal of industri:ll w;istc’ an owrvicv.‘. .\lossoc~lr~rsclls Irrstitut~~ vj’ T~~l~rwlo~~~~, Twltrwlo~~~ Rcvim’ 73(S): 213.

Kirb),. C. I-. 1967. Irrigation with waste \vatcr at the .Bonrd ul \\‘orks Farm. Wcrribcc. S.vJ,rposirtrJl 011 Wafer 011 the Farm Water Rcscarch I:ounda1lon oi Austr:llia Report No. 25. (P.O. Bos 47, Kingsford, New South Wales 2037, Australkl.)

Malina, J. S., and 13. I’., Sagic. 1974. Vinrs Sm~ival irl li’alcr ard h’us~tw~attpr Trearmcnt. Cci~tcr for licscxrch in Water Rcsourccs. The University ot‘ Tcx;~s, ,4ustin, Texas (In plus.)

Metcalf and ltddy, Inc. 1973. kJusltww!cr ‘fr~otr~rc’rr~ ar~tl Rtww II,,, 1.und .-lpplic-uriclrr. (2 Vol.) Rcporl No. EPA-660/2-73-006; U.S. Govcrnmcnt I’rinflng Office. Wash- ington, D.C. 20402, USA. (Vol. 1: U.S.$l.lO;Vol. 2: U.Q.S2.40)

National Association of State Univcrsitics and Land-Grant Collcgcs. 197-i. Recr~cliqq Mur~ici,txd Slud~cs ard I~~@cJtts ott Lad. Kcport No. PB 227-lS4A/S. (National ‘I’cchnic;d Information Scrvicc, U.S. Dcpartmcnt of Commcr~c. Springfield. ViFinllt 22151, US/i. U.S.$6.00.)

Soppcr. W. 17., L PIntI L. T. Kardos, cds. 1973. Rccycliqq Trcu(td :~lllrli~ilwlClt’ustt,~~~utt~r atd S/rrdxc Ilmirg/:lr Forcsl and CZop/and. Pcnnsy Ivania Stale Univcrl;it), I’rcss, University Park and London. 479 p.

Special Report on Land Disposal. 1973. .lourrtal 01’ r11c Ilk~rcr Pollic liott C’ontrol Fdcra~ior~ 45:1465-1507.

Wolman, A. 1948. Industrial water supply from processed sewage treatment plant effluent at Baltimore, Maryland. Scwuagc I\Jorks Jourml 20 : 15.

Municipal Recicling ,

Atilcric;ln k*icty. of Civil linginccrs Committee on I~nvironmcntal Quality hlanagcmcnt. 1970. I<nginceiing evaluation ol virus hazard in w;ltcr, .IowJlul (~1‘ ~lrcp S’arrllary f~rr~iJrt’t!rirr~ Divisiorl, ,4 mcricatr Socic(~* oj’ &vi1 i:‘JrgiJwers 96(SAL): 1 I 1 .

Stander, G. J., and J. Funk. 1969. Direct cycle \v:ltcr rcusc provides drinking water in South Africa. IlJakr nJ~d HJastrs fYJlgirleerirr,y G(5): 66.

I

General r

Gulp, G. L., and R. W. Culp. 19.71: Ad~unccd I$Joste\oarer Tbeatrtlerrt. Van Nostrand Reinhold Co., New York.

Fair? G. M., and J. C. Geyer. 1968. Wafer md Wasrewafer Etrg'rreerirrg Volume 2. John Wiiey , New York.

Gavis, J. 1971. Wastewater Rense. (Pregared for the National Water Comti&$ ‘. National Technical Information Service, Springfield, Virginia 2215 1, USA, Accession

No. PB 210-535. _’

Advantages

The important advantage of \yater reuse is that it can. if properly managed, reduce by severalfold the demand on water from natural sources. Contin- uously recycling 50 percent of the wastewater in effect doubles the water supply.

industry may provide In some arid locatio!~s reusing wastcwatcr in additional water nccdcd to FIrnit industrializati~,ll tl 1

be feasible. . . C””

Limitations e .’

In any rcusc scheme these major constituents of wastewater hqv~ to be considered: ‘Y

Pathogenic bacteria and viruses ‘Parasite eggs Heavy m’etals ’ ’ , salts Nitrates

A’ --”

-4 >

,

50 MORE WATkR FOR ARID LANDS

Pathogenic bacteria can be killed by chlorine disinfection, but the remain- ing hazard from viruses-after advanced waste treatment is not known. Al- though few outbreaks of epidemic virus diseases have been attributable to transmission in water supplies, the prevailing view is that present known treatment processes remove the hazard only if very carefully controlled.” Too much uncertainty exists to certify water from even advanced treatment proccsscs as viralogically safe. Though this increases reluctance to USC treated wastewatcr for drinking or for irrigating vcgctablcs that arc eaten fresh, it should,Lnot hinder jts USC for less critical purposes.

To I-c&c water without causing cnvironmcn’tal disaster calls for good managcmcnt and a good understanding of the user’s rcquircmcnts. Systems can easily be mishandled and cause serious disease or harm to the environment. ‘If more than 50 percent of the water supply is wastewater. salt accumulation can cause serious problems whether the water is for agriculture. industry, or municipal use.

Assimilative disposal of wastes on the land, which dots no permanent datnagc,‘is clearly ;I very different thing from uncontrolled dumping, which destroys the soil and may lead to serious pollution of ground water. Far too few cngncers have a feel for proper r?tes of application to th!-soil. They forget that a little $00 much can change dilu’tion to pollutio>4f-.you want to USC a l’arm or a forest as a dis

7% farmer or foresier to manage it.- osal site, there is noytltutc for a good

The cost and difficulty of reusing water depend on the treatment processes needed. Some secondary and most tertiary treatments require large capital investment and trained, capable personnel. Operating costs -are high, in many cases too high for water reuse to be feasible. In arid-regions the cost structure is more favorable. Direct reu+se for potable supplies may have to over&me aesthetic objections, even if the water is demonstrably pure. Furthermore, people may object to eating food grodn with human waste. Reusing water will often require that all sectors-agriculture, industry, and urban adminis- tra tions-bc integrated in management and policy.


Reuse of water has been practiced ever since people have taken water from rivers. Thus, in a sense, it is not new. Along rivers such as the Ganges, Nile, and Mississippi individuals, pommunities, and industry reuse the water:&ny times over. There is no evidence that this causes harm. This chaptef deals,

,_I

“Matins and Sagic. 1974. (See Selected Readings.) __,- -.

__ ’ ,.-. 2oDean. 1971. (See Selected peadings.) I)

REUSING WATf:R ,” ,’ n : 5::

Metcalf’ and f.1ddy, Inc. 1972. Ii~us~cwotcr I:‘rl,+r;ecriq, McGraw flill. Ncu, York. 7S2 p. National Water Commission. 1973. p 306-3 15. (See Sclcctcd Readings, p. 5.) l&S. Department of f-lousing and Urban Development, Office of International Affairs.

-’ 19’70. %Wage Lagoons foT Developing Countries. Ideas und Methods Exchange NO. 62.35 p. (Available from the authoring institution, Washington, D.C. 20410. US.%)

Weber, W. I., Jr. 1972. Physiod~etnicol Processes for Wafer Qzrarlit.v Corltrol U’ile~~ Inrer- science Co., New York. 1L

Contacts

hmcrican Public Works Association, 13 13 Last 60th Street, Chicago, Illinnls 60637, USA

l~urca~l 01’ S:lnilary Icnginccring, St3tc of C’ali1‘~lrni;i, Dcfl:lrlnicnl ill’ l’ul>l~c Ilc;~llh, Ucrkclcy, Calil‘orni;l 94720, USA (E. Scpp)

(‘cnlral I’uhlic f Ic;iltli f~+incrcring licscarcl1 Institute. Nagpur, \lallar;l\tlrr;l. III~I;I (Ci. 13. Sl1cntlc)

Collcgc of AgriculturC, University ol‘ Arizona. Tucson, Arizona HS72 I, LISA (C. II. (‘luft‘, A. D. Day, and ‘I’. C. Tucker)

Civil Engineering Department, University of Nairobi, Nairobi,‘Kcny:l (Ii. lows) Civil f:nginccring -DcFartmcnt, University of Tcsas, Austin, ‘I-c\a\ 757 I?. L:S!1 ’

(J. I:. Malina) Community Water Sup&y and Sanitation,

, Division of f&ironmcntal Health, World

Ilcalth Organiz:ltion, (~IICV;I, Switzerland (L. A. Orihucla) ” J)cpartmcnt of Soil Scicncc, Univcrsity.ol’ California ;I( Rivcrsjclc, Rivcrsldc, California

9250 I ) USA (A. L. l’agc)

Dcpartnwnt of Water AtTairs, South-West Africa Branch, Windhuck, South-West AI’rlc;l (Namibia) (S. W. Burger)

I)(:fxlrtmcnt of Wntcrshcd Managcmcnt, University, of Arizona, Tucson, Arizona S572 I , USA (G. S. Ixli~ii;in and L. G. Wilson) ’

I:,livir~)lltncrlt;II Il~alth Laboratory,, I-Icbrclv University of Jcrus;~lcm. Jcrux~lcm. I.sr;~cl (II. I. sIlllv;ll)

Institute for Research on Land :lnd Water Resources, Pcnnsylv;ml;l SI;I~C’ Univcrslty,

University Park, Pcnnsylvani;l 16802, USA (W. 1;. Soppcr) lnstitutc for Water, Berlin, Germany (W. NiemitQ Instituto DC lninicro Sanitaria, Urliwrsidad De Buenos Aires, Uucnos Aires, hrgcntina

(R. A. Trcllcs) Melbourne and Metropolitan Board of Works. 625 Little Collins Street, blelbourne,

Victoria, Australia E, Municipal Treatment and Reuse Section, Advanced Waste Treatment, Environmrntal

Protection Agency, Cincinnati, Ohio 45268, USA (R. 6. Dwn) h4uskcgyu Ch~lp Dcfxlrtmcnt of Public Works. hll!skcgon, \l~cll~gan 49440. US.A

(J-: C. I’ostlc\~ait) National Institute .for Wdtcr Rcscarch, Cou’ncil for Scicntilic ;tnd Induslrial 1~esc;lrc.h.

P.O. Bos 395, l’rctoria, South Africa Negcv lnstitutc for Arid Zone Rcscauch, Seer Shcva, Israel (J. Schucttr) OL‘Iicc of Water Programs Operations, U.S. Environmental Protection Agency. f\‘ash,-

ingttin, D.C. 20460, USA (B. L. Scabrook) Robert &, Kerr Environmental Research Laboratory, Environmental Protection Agency,

P.O. B’ox 1198; Ada: Oklahoma ‘74820, USA (C. Harlin, R. Thomas) U.S. Water Conservation Laboratory, U.S. Department of Agriculture, ARS, Phoenix,

Arizona, 85040, USA (H. Bouwer)

Dug Wells

l-land-dug ~~11s (FIGURE 33); have beenuse& for thousands of years but have bccomc less popular with the advent of tube ~~11s.~~ Today, interest in dug wells is reviving, and they still hold much promi& for arid lands. Modern

I materials, tools, and equipment may transform crude holes in th!Y% ground, hosts for parasitic and bacterial diseases, into more safe, soundl+rigineered: hygienic, and reliable sources of water.23 Dug wells are inexpensive and.easy to construct and maintain by fairly unskilled labor. They provide stoiage for water, as well as a source. -I.

In most casts dug wclls,~will be superscdcd b>rtubc wells, but they provide an important tranSition step, and in some>ases, dug wells will always be best, e.g., for shallow, low-yielding aquifers and for inaccessible regions where transporting drilling cquipmcnt is difficult.

In Afghanistan and India, dug wells arc being seriously acconsidored.24 *i -9 Since about 1954, when the use of air compressors and rock drills became

COII~~~, many existing dug wells on the Deccan plateau of central India have been deepened by digging through lava flows that had blocked previous equipment. In the last IO years India has also improved many dug wells solely by ‘adding pumps. Powered by internal-combustion engines or electric motors, inexpensive centrifugal ‘or turbine-type pumps, installed on platforms l-2 m above the water Icvcl, boost the water up to ground level. Suitable pumps are now made in many developing countries, including India and Pakistan. ’

.

Dug wells, however, do have distinct limitations: .= They cannot bc used to reach groundwater deeper than 20-30 IN. l Their water production is usually low. l Well-digging technology is understood and used in most countries,‘but ”

the art of lining wells has regressed, and there is an important need for improved linings. The liner protects against caving and collapse and prevents

22Gibson andSinger. 1969. (See Selected Readings;) 23Wagner and Lanoix. 1959. (See Selected Readings.)

54

II

56 MORE WATER I;OR ARID LANDS

polluted surface water from entering the well. The main problem is lini!g the . ’ walls below the level of the water table.

Another need is for safer, more rapid, more efficient digging techniques.

Qanats

A qanat is, essentially, a horizontal tunnel that taps underground water in an al’luvial fan and, withobt pumps or equipment, brings it to the surface so that it can bc used.

A qarlat system is co’mposcd of three csscntial parts (FIGUKE 34): l ‘One or more vertical h?ad wellsGdug into the- water-bearing layers 01

the alluvial fan to collect the &tcr. 0 A gently downward-sitiping underground horizontal tunnel Icurling the

water from the head wells to a lower point al the surface. (In part. the tunnel acts as a subsurface drain to collect water.)

o A series of vertical shafts between *the ground su,Fface and the‘ tunnel. for ventilation and removal of excavated debris (FIGURE 35).

Bccausc qanats deliver water without pumps and pumping c&sls (FIGURE 36), they can -be used where pumped wells arc loo cspensivc to opcratc.

Qanats vary greatly in length, depending on the depth of the aquifer and the slope of the ground. The conduit from the head wefl to the mouth may cxlentl l-4 km; one in southern Iran is more than 28 km. Com~nmly, the length is IO- 16 km. The water obtainable from individual qanats also varies; a study of 200 in the Varamin plain southcast of Tchrran, Iran, mcasurcd the largest yield at 270 liters per second and the smallest at 1 liter per -+ second.” 5

About 3,000 years ago the Persians learned to dig qanats (an ancient Semitic word and ancestor of the word canal) to bring mountain groundwater to arid .plains. Their qanats were built on a scale rivaling the great Rooman aqueducts. The system has since been used in various places from Pakistan to North Africa. In Afghanistan and Pakistan they are cxllledz korezes, in North Africa, ji~gqaras, and in the United Arab Emirates, #lilj. Though new qanats are seldom built today, many old ones arc still used,/especially in Afghanistan and in Iran, where there ;Lre some 40,000 qanaiis comprising more than 270,OOO’km of underground channels that supply $5 percent of the country’s I water.

In Iran areas with only 150-250 mm of ar$ual rainfall grow their own food and even produce cotton, dried fruit$, and oilseeds for export- achievements made possible by qanats. Until &cently (before the Karaj Dam was built), the 2 million inhabitants of Teh&an tapped the foothills of the

_ 24Government of India, MiniStry of Food tia Agriculture. 1862. (See Selected Re@ngs.) I

58 MORE WATER FOR A RID LANDS

FIGURE 35 ROW oT craters, each marking the mouth UT a qannt ventilation &aft, i across an arid plain in wcstcrn Iran. Crater w;\lls pi-utcct the shafts and the tunnel below from erosion caused by the inllow bf water during n heavy dcscrt rainstorm (ICAO) 4

Elburz Mountains with qanats for their entire water supply. The agricultural production made possible by qanats repays the investme.nt cost for construction and qaintenance. In 196’Pthe return on investments from the sale of water and ciops ranged from 10 to 25 percent per annum depending on the size of the qanat, the yield of water, and the crop.25

‘A recent innoyation now Csed in Iran is a hybrid between a dug well and a qanat. A dug well is excavated ,to kelow the. water table and then horizontal galle,ries are bored out, u&g the excavhticg methods of the qanat builders. In the dug-well shaft a centrifugal pump is then @stalled to piimp to the surface the water collected by tlik horizontal galleries.

Qanats have limitatibns: . They usually flow continuously and year-round, so unused water is

wasted. Flow is maximum during the rainy season when the demand for irrigation is least and minimum during the major irrigation period (summer). Qanats may dry up altogether in &ought years.

. They serve the lower elevations of alluvial fans, which tend to have more saline and poorer soils than do the higher elevations.

25Wulff. 1968. (See Selected Readings.)’ ’

FIGURE 36 Water flowing out the main qanat of Dusadj village, Iran, is used mainly for irrigation. A qanat can deliver water $I’ otherlvise very arid terrain. (FAO) ’ -.

D Qanat water is often of poorer quality than, water “from wells drilled higher ill the alluvial fan. L

. Qanats are expensive and dangerous to build by the ,piimitive hand- tunneling methods of the past, and in’ receni years construction costs have increased along with rising standards of living and labor costs. However, if mddern engineering, geology, hydrology, and remote sensing are applied, the qanat principle could play a role in future water production in arid lands.

Research is needed on safe construction methods, on qanat linings that increase safety and decrease maintenance, and on ways to shut off the water .flow when it is not needed.

4 ,-

FIGURE 37 A compl.cted horizontal well on test yields over 50 gpm. Plumbing hcud includes two tees, a shutoff vnlvc to rcgulatc the flow, ;1 v;1cuum rclicf. 2nd ;I pipe ) rcduccr. (W. T. Wclchert) ’

FIGURE 38 Drilling a horizontal well. A standard well casing ti diifled on a slight downward slope. Equipment is light and portable and easily tiansported evenin remote, rough terrain. (W. T. Welchert) ..’

. .

I~IGukI: 39 ’ Good sites for horizcm tal wells arc dike fprma- tions, impervious geologically tilt: ed clay, or rock Wtlls that forin ;I natural darn. (\I’. I‘. Wclcl1crt )

Water Table

Hori i

ontal Wells

\

e

In t lc dcvclopnient of water supplies, small SIlrings arc ot‘lcn ncglcctcd. p Yet in I ‘any rcniotc and arid niountai springs arc the SX~CSI and nlost dc xndablc source o1‘ water I’OI nits t ic use. The horizontal well system, an improved spring-dcvclopme has great potential for providing ; nd conserving sanitary water in geologically appropriate ;1rexs.

A horizkntal well is a “cased” spring (FIGURE 37). A horizontal boring. rig (FIGURE 38) IS used to drill a hole and install a steel pipccasing into a mountain or hillside to tap a trapped water supply (FIGLIRE 39).

Tapping water frdm springs is an ancient art. Convent ly, when II seep ’ or spring is located, it is either dug or dynamited to espo e watc<I,bearing rock. Results are erratic and always carry a risk of damaging the natural bar&r that dams the underground reservoir. The flow. once established ths way, is almost impossible 10 control ahd my result in rapid depletion of the : aquifer. r

I-Iorizqntal wells virtually eliminate these hazards. They< xc drilled at promising sites where springs, seeps, or tracts of water arc t‘ound. Occurrcnw of phreatophytcs (chapt‘iir 13), dried-up springs. and favorable geology arg all indicators used to select the drilling site. A horizontal well can tap the aquifer with precision and safety. Furlhermore, it prot;cts against contamination by animals, dust, erosiofi, etc. No pumps are needed. Maintenance costs and problems are insignificant in comparison to those of other systems for harnessing springs. b 9

If the flow is very lorv,,a storage tank can be added to accumulate water during the night or off-season. With adequate storage, spring sites that flow only during a few weeks in the year may be useful:

I J

62

’ During the last 15 years about 2:OOO succcssfui l!orizontal wClls have been drilled kin arid areas of the southwestern United States. A 1967 University of. Arizona study indicates that a servic’eablc. water supply was obtained at 45 out of 53 locations tried during-one program. Successful yields varied from l-230 l/minuted; most were in the lo-40 l/minute range. Drilling kne averaged 32.3 hours per producing ~~11.~ 6

Horizontal drilling equipment is currently manufactured; ‘it is simple. portabk, and dependable. The drilling process involves ;i rotary. wet-boring horiz~~lltal drill stem rig (FIGURE 38), h’carbidc-tipped or dixnond-corc drill bit, ;I small recirculating water pump! a ccmcnt xlurly prc‘ssurc tank, ;I drill water s~~pply. and a few standard plumbing tools and suppl~cs.

I-lori/.ontaI-well. drilling is qu~tc a dil‘l’crcllt tccllnolr)g~ /‘ronI vcrtlcal drilling. Skill, paticncc, and I‘icld cspcricrlcc ;IW rcqulrcd ‘to master It.

Selected Readings ’

. Dug We)ls

Horizontal Wells /

Frccmnn, B. N. iIorizotrta1 Wells. A’cH~ Wufcr So~rrt~c~. I~~v~-~lu~~utc‘ mutton film pro&rccd by Deere ungl Company x 2 public service. Contact. Advcrtismg Department, Dccrc arrd Company, Moline. Illinois 61265, USA.

Welch&t, W. T., and B. N. Freeman. 1973. ‘Horizontal’ Wells. .loun~al ~j.Ruugc !1l’ar1agc- metzt 26(4):253-6. Also available in Spanish ;LS: Pazos Horizontales. Selecciotles de1 Jomral of’ Ratlge Management 2(4). Agosto 197 3.

26Welchert and Freeman. 197.3. (See Selected Readings.)

WELLS ,, 63

- Contacts

Dug Wells :& Ministry of Agriculture, ‘Government of? India, K.rishi, Bhawan, New Delh&india

(J. I(. Jain, Irrigation Adviser) .I

Service especial de Saude Publica, Government of Brazil, Brasilia, Brazil University of the Negev, Beer Sheva, Israel (A. Issar)

Horizontal Weils “, ‘: i

Ctiopcrativc kstcrkion Scrvicc and Agricultural Espcrimcnt Station, University of Arizona, Tucson, Arizona 8572 1, USA (w. T. Wclchcrt)

I ‘\,

1. .

R

,

.

. 9 n .

.

‘6 Oth& Sburces of Water ,’

,s This chapter briefly ‘mentions some other sources of water?n arid lands - that are either more thtn adequately described in literature elsewhere or too

. hifly%peculative [o qrarraht more specific treatment in a general report. . ’ D -I .Li I 0 ‘. Q’

1 ’ Grbundwater Mining 1 c a ,.

. .

kany productive aquifers in arid regions of the, world are storing large qiantities of water that can be iapped by well-k;;%n deep-well extraotive

‘60 ‘techniq?ies. Aquifers of this-type are%:idespread beneath deserts in northern ’ Mexico, southwestern United States, North Africa, eastern Saudi Arabia, the

Sinai, and elsewhere ,in ‘southwest Asia. The water in such aquifers is not * naturally replaced once it is pthdrawn; it must be’considered a “wasting asset”

2 like any other mineral commodity. Its development must be under-

taken with the full understanding that usually within a few decades the supply will be’i;depleted and capital investments must be amortized within that time. Under some conditions these aquifers may provide interim supplies” to generate capital to underwrite expensive systems that bring in a more permanent supply of water., from outside the region. Development of such _ aquifers is noiv proceeding in se&al parts-&-Algeria, Libya (FIGURE 63) Egypt, Saudi Arabia, Ivlexico, and-the United States. I-S . , .

@ I I ”

I Desalting

Low-cost desalting of seakater would be a boon to’arg:lands bordering seas or’ ,salt lakes; over the past few decades many proposals to build huge distillation plants to produce water for agriculture have been widely advertised and intensively promoted. Although new and @roved desaltihng methods using membranes and ion exchange have been developed, noimethdd can yet promise truly low-cost freshwater. Current promises of cost reductioi for distillation plants are based on the assumption that the cost of the product ‘decreases as the ,size of the plant increases. But a practical limit 1 exists to cost mduction achieved by this means. Also, there are problems in I\‘. .

64 I,<

i c

1

OTHER WATER SOURCES \, i 65 ,.=i .I r; ‘. I

disposing‘ of huge quantities of hot brine, pumping andqconveying desalted water to the point of use; and storing it until needed for irrigation. Another’ fundamental problem is that desalting plants require large amounts of energy to construct and-operate. L , ’

Most, proponents of desalting schemes now agree tha,t the water will be too expensive for use in ,irrigation as practiced today. However, desalination of sea or brackish water could prove economically rewarding in special situations such as tourist centers.

Distillation plants producing up to several million gallons per day are c commercially available and are already used for’ domestic and industrial

purposes in some very arid regions where the local economy can afford it.

Solar Distillation - *

In solar distillation the-sun’s radiation passes through a transparent cover on’ to a source of ~brine; water evaporates from the brine; and the vapor condenses on the cover,which is arranged to collect and store it. It was first used in Chile’s Atacama Desert in 1872 in a plant supplying drinking water for livestock used in nitrate mining. The plant reportedly operated for .30: ‘\ years.

The process .today is generally in the pilot stages, though small community-scale stills are close to extensive commercial application. Durable designs requiring little day-to-day attention and operating with minimal maintenance have been developed in the United States, France, Spain, and

z Australia (FIGURE 40). Solar distillation is.now:,q{ed on a’small commercial c scale to supply small towns” in isolated areas of Australia and small communities in the Mediterranean basin; and the Eribbean. Modern research into solar distillation is emphasizing new:materials and designs for economical and durable construction to reduce product-water cost.

I

1

:%+ -us ‘V Remote Sensing’for Detecti ;g Water ’ ;, I

The use of photographs from satellites and high-flying aircraft is a newly ~‘\,, developing tool !hat is proving,useful for @annersin arid lands. The following ’

- are a few successful uses of such remotesensing. c n

jr,

l Open-water oasm have been detected, and repetitive imagery has been 8 ~1

used-to determine their transience. ;.g

l Geological information for determining the shape and extent of underground aquifers has been/obtained from most types of remotely -obtained imagery, including rad& thermal, and optical &rages from aircraft”‘. or

2’ k,

66 MORE WATER FOR ARID LANDS D

FIGURE 40 Solar still at Caiguna, Western Australia. Waste heat from a nearby internal combustion engine suiplements the solar heat, markedly increasing the still’s efficiency. (Commonwealth’ Scientific and Industrial Research Organization, Highett, Victoria, Australia)

>./

.d

satellites. Airborne geophysicalisensors, such as magnetometers, are also useful in mapping underground structures that c&-&o1 groundwater movement and distribution.

0 The extent of springs, seeps, and shallow groundwater in alluvial channels is often mappable, even from satellites, because trees and shrubs ‘23 associated with moisture can be detected. *

0 Effects of rainstorms on the desert can be detected; after a storm, the da&er tones of the moist soil can be seen, and a few weeks later vegetation responding to the moisture is reveafed.

9 Plumes ofofreshwater from offshore submarine springs can be detected with the use of thermal scanners because they usually differ in water temperature from the surrounding sea.

l , The extent and movement of floodwaters have been mapped. - 9 , The snow cover on mountains has been determined in order to estimate the amount of runoff water that will be available at lower altitudes after the 1 thaw.

B P

The following topics are included solely to give some cautions and a sense of the range of current speculation about water supplies for the distant future. u’ 1

, c . .

OTHER WATER - _ -=.*

SOURCES‘ r!

Rainfall Augmentation \, -,

.

Certain cloudfqrrnations contain supercooled water; rainfall augmentation hastens precipit,atio&‘of this water. Adding ice, frozen carbon dioxide, and silver iodide-whose crystal shapes prornot~corrdensat~pn (nucleation) of supercooled water-causes Dramatic ice-crystal formation and produces rain. This method is known as cloud ieeding. ’

To produce rain by cloud seeding, one must always have the right r

.

meteorological conditions. .Even then the seeding “can sometimes lead to more precipitation, can sometimes lead to less precipitation. and at other ‘times the nuclei have no effect.‘12 7 ’

Though there is keen interest in cloud” seeding in arid lands. experience indicates that its best opportunities for increasing precipitation are in areas where cold, wet air masses are-swept upward over mountain ranges. Prospects for increasing precipitation over low-lying arid lands do not seem promising, primarily because of the scarcity,.of water-rich clouds. Arid lands. that benefit from cloud,, seeding will probably be. those fed by streams originating in mountains.,’

The results of cloud s&ding are diffjcult to*pl;edict because of the still, imperfect knowledge of the physical processes causing precipitation and . because of engineering difficulties in getting seeds into c& in optimum >?i amounts and at the right time and place. A related uncertamty is whether seeding clouds in one area modifies precipitation in another. Detailed physical ‘- analysis of some, cloud systems may, in the future, allow one to predict the ” effects of cloud seeding, but research is in the very early stages. .

i

Icebergs

Eighty-five percent of the world’s freshwater is trapped as ice in the polar‘ regions, but it is generally considered unusable. Engineers, glaciologists, and physicists are now speculating on whether it could be profitably recovered by’ towing’icebergs to water-short regions. According to some, “the idea appears both technically feasible and economically attractive and merits serious consi&23rt5i.“2 a

N

Data on size and distribution of icebergs indicate that the ply is more than adequate, and satellites can be’used to select suitable

icebergs. Prime producing sites in the Antarctic could supply icebergs ,for..

,‘./ Australia, the Atacama Desert in Chile, and other arid regions of the 1 Southern, and perhaps even the Northern; Hemisphere. p

“Committee on .+Atmospheric Sciences, National Academy. .of Sciences-National , 2gResearch Council. 1973. (See SelectedlReadings.)

Weeks and Campbell. 1973. (See Selected Readings.)

68

.

MORE WATER FOR ARID LANDS I

The icebergs are +ere; the problem is to gnove them. According to one report ,2 8 a hypothetical supertug, which could be built with “,present technology, could tqw icebergs up td 16 km long, 3.5 km wide, and 200 m thick. On delivery, the water in such icebergs would be worth hundreds of n millions of dollars.

Melting losses are important because transit times at reasonable towing speeds may csceed IO0 .days and water tcmpcr;dtures’ orl?tl~c deliver-v sites cxrecd, I S’C. Unfortunately, detailed calculatiJi@ and adequate field obsc~-w

lions to .accur;Itcly predict towing speeds and mcltinh rq,tcs still need to bc dnnc.

f

Two inhcrcnt problems arc gutting the ice to melt at thc,cnd of the tow, and pumping the water from sea level into the supply system. Pcrhrlps the ice could provide i “cold sink” for ‘coastal p&verplants; tlius. waste heat would

s be utilized for melting ice and the thermodynamic cfficien2y. of the powerplant increased. .t b

x ,:

As with other water-resoucre exploitaiion prop&s, critical techjlology assessment must prcceclc any decision that iccbcrg harvcsfing is ;1 realistic, desirable .possibility. In particular, iccbcrg-llarvcsting proposals. rtiisc intcrna- [ional legal and polili$al questions coriccrning resource rights-.nizttcrs of uncertainty in the dclicatc Ant-arctic ?&~~iy regime and matters of very .‘P, *intense negotiation ia the ejncrging restructuiing of the law of, the sea. Additionally, as the importance of the polar regions to wo,rld climrltc. has become increasingly evident, it has becomc cclually evident that not enough is known of the physbcal basis of climate to permit confident prediction of the . extended effects of even apparently small modifications of the polar ice environment.

Dew and Fog Harvesting

. .

The possibility of condensing water from the atmosphcrc by some simple sc1~1no has intrigued several investigators. Some have suKqested that ancient, civilizations accomplished it for agricultural purposes. “Dew JllWJldS” in the Negcv (FIGURE 4) and the ancient “aerial wells” of Theodosia in thc,Crimca ’ were piles of rocks that’ supposedly cooled during the night and condensed ’ the early morning dew. Experiments have been unable to show that this procesi occurs to any significant extent, and the supposed dew mounds of the Negev have now’ been shown to result from soil-smoothing operations to increase rainfall runoff2 ’ (chapter 1). Dew will condense on piles of rock, but riot in harvestable and usable quantities.

j,\28Wceks and Campbell. 1973. (See Selected Readings.) , w 29

-- Evenari, Shanan, and Tadmor. 197 1. p. 127. (See Selected Rcgdings.) ‘. I

I

I . . :_ _ d .

Selected Readings

Groundwater Mining /

i United Nations, Departmen; of Economic and Social Affairs. 1973. C;rmtd hbtcr tt1 rlfiica. Report No. ST/EGA/147. (UN Publication Sales No. c.71.11.X.16.) linltcd Nations, New York. 170 p, .

Vahra, 13. 13. 1972. Qwr,~tf I(lnwr Cmc.; tzj .,i,qc’ SottIC 1’011cjl Ittrpliculiotrr \llnlctr) 01 . A~\ric~ulturc. Ncw$klhi, India. J;lnu:iry 3i , 1972. S 11.

Desa!ting

Solar Distillation

Rainfall Augmentatign’

Committee on Atmospheric Skenks. National Research Council. 197 3. b’calhcr atid Clittmte, Modificurion. Probler?~s and Proyress. National Academy of Sciences. Washi&ton, D.C. 258 p. (U.S.S6.25)

Center of! Scientific and Technological Inforniation. Arrifi‘cial Rairlfull .Ve\~qsleffer. A monthly rcvicw,with abstracts from technical literature. i\vailable from the authoring institutiort, P.O. Bos 20125, Tel Aviv, Israel (U.S.Sl8.00iycar)

. .

70 #ORE WATER FOR ARID LANDS

Hult, J. L., a&l N. C. Ostrander. 1973. Anfarcric fcebetgs as a Global Fresh’ Warer -Resource. Report. No. R-1255-NSF. National Science Foundation, Washington, DC., .-Tg&& ; l

Hult, J. L., and N. C. Ostrander. 1973. Applicability of ERTS for Surveying .&ta.rctic I&berg. Resources. Report No, R-1354-NASA/NSF. Goddard Space Flight Center, Greenbelt,. Maryland 20770. USA. 6 .

Weeks, W. F!, afnci_w. J. Campbell. 1973. Icebergs as a fresh water source: an appraisal. ” , . .Jouma[ ofGlaciology. 12:6$.

I I l

D - #

“-_ 1

.a B s

,I

Dew and Fog Harvesting

IXii%i, M.; I+ Shanan:Yind‘N. Tadmor.’ I-971. 77tc Nr?gcu: 7’@ Challer~~c ofu Dcscrr. Harvard University Press, Cambridge, Massachusetts, USA. pp. 12647. ’

Gindcl, I. 1965. Irrigation of plants with atmospheric water within the desert. Nonlrc. 207:1173-5. 1 3’ . (_‘ , 0

P a

aft

I

r

7 Reducing Evaporation from ‘Water Surfaces

‘,( J 4: Reservoirs and canals in arid lands arc subject to llcavy cvaIx~r’ali~x1 Ioss@~!~~,

ht because cvapora ting water is invisible thcsc losses arc-~ ot‘tcn recognized. From small reservoirs, stock tanks. and farm poi& with surface areas open to the air (compared to’ the volume of water stor evaporation losses often exceed the amount of water used productively. 1

Reducing evaporation is an import’ant way to incrcasc the supply of wat It iricrcascs rcscrvoir capacity withou1 new construction; iI1 arid rcglo may mean the dil‘l‘crcnce bct&xn a dry reservoir and ;I lillcd orlc. .c+ .? .,

Gcncral~y y, the method tbr reducing evaporation ha,s been to cover ‘the water surface with a barrier that inhibits vaporization. $rTsmull trinks. 3 cover or roof is an obvibus choicc,.but for ponds and larger rcscrvoirs the solution is less simple. Fot”thc latter the methods tested inoludc the following: liquid chemicals that au!omatically spread out, forming a sealant layer across the surface; blocks, rafts; or beads that float on the water surface and reduce the arca ‘where vaporization can occur; and storing0 the water in sand- and rock-llllcd dams. I

Liquid Chemicals .

Aliptiatlc alcohols, e.g., cetyl alcohol, arc long slcndcr molc~ules that align Ihemselves side-by-side on a water surface’. covering it to <aform a film 1 molecule thick. Considerable research and publicity have been dcvotcd to t.he possibility of using such films to reduce evaporation from water surfaces. Unfortunately, the films do not reduce the a’motint of solar en&g the- water absorbs, and they decrease the amount of heat normally lost from the water because inhibiting evaporation also -inhibits the cooling eifects of vaporization. Although evaporation decreases where the alFoho1 layer is intact, the higher water tcmpcraturc incrcgses evaporation at any part of the water

,.

7.4 . . . . . . . . . . , . . . , . . ,..I .,....,........ j.,....,. MORE WATER FOR ARID LANDS

i FIGURE 41 Ah experiment in Arizona, USA, using wax to suppress evaporation. Blocks of wax have been added to the tank (foreground). Sun’s heat melts the wax to form the continuous film visible on the tanks in the background. During 4 years this film has suppressed over 85 percent of the normal evaporation. (K..C. Cooley)

!’ .* k ‘$’ . 6 *.’ surface the barrier does not cover. Furthermore, an intact al~cohol b-wrier is impossible to maintain because of wind and wave action. These problems make the method impractical today,

The aliphatic alcohol molecular monolayer is, nonetheless, a .tempting and potentially rewarding concept: it requires only small amounts of materials (less than 60 g per ha of water surface); it reportedly does not restrict the ‘. transmission of oxygen to the water; and it consists of materials that are j.;. nontoxic to fish or humans. Attempts are now under way to circumvent the : problem of maintaining a continuous film on the water surface. One approach uses a plastic net to restrict the drift and disruption of alcohol layers.

Wax

Wax is an unusual, recently tested evaporation suppressant. Floating blocks of wax are added to the kater; in sunlight they soften and flow to form a flexible, continuous film. In Arizona, a wax cover on a small tank (FIGURE 41) is still in good condition after 4 years; the evaporation- suppressing efficiency is over 85 percent. Even if the film cracks and breaks during cold weather, the sun’s heat subsequently re-forms it.

d . ’

‘REDUCING EVAPORATLON FROM WATER,’ 75

FIGURE 42 Protective covering of molded,.lightweight, concrete slabs’?ut evaporation by an estimated 80 percent recent4y??fulLscale tests on two reservoirs in Ovamboland,

’ South-West Africa. Engineers cover reservoirs with 24-in’, 2-in thick floating slabs 01 polystyrene, sand, and concrete. iZxpose&surface of each slab is painted white to reflect the intense sun rays, which hasten evaporation.

I

The specific gravity of the material (0.8) keeps about 80 percent of the floating slab submerged, reducing the possibility of piling up in heavy winds. Submerged portion of the slab is coated with bitumen for d.urability and to prevent the material from affect,ing the taste of the water. Slabs have rounded comers to permit the large body of water underneath to breathe properly when covered with the densely packed slabs. (National Institute for Water Research, South Africa)

Sol id Blocks

Floating materials, covering the water surface, reduce the area where evaporation ‘can occur. Blocks of lightweight cbncrcte, polystyrene, wax, rubber, and plastic are under trial as evaporation rctqdants. Floating concrete blocks, made with lightweight aggregates, ha$ee been used JO rcducc evaporation from a 10,000 n-r2 reservoir in South-West Africa3’ (FIGURE 42).

To overcome the water heating that is an inherent problem in evaporation suppression, researchers are working with, floats. made of insulating and light-colored reflecting materials that prevent solar energy from entering the water. For examp?le, sheets of inexpensive and highly insulating expanded- polystyrene, 2.5 cm thick and coated with asphalt and gravel have been

..!‘Concrete slabs’cut reservoir losses. 1966. (See Selected Readings.)

tcstcd. Coupled togcthcr with incspcnsivc clamps to I‘~~rni Iaigc rifts up 10 160 m2, they can form c~ccilm energy anti vapor barriers. (See FlGURL% 24,’ p. 33; and 43.) F oame$ butyl rubber can also be effective; thou& espensivc, it may last for over 10 yqars!

7 “\~; I’

Sand-,;illed Reservoirs

Evaporation can bc. controlled by filling rcscrvoirs with sand and loose ,2,. rock. Water is stored X’thc pc rcs bctwcerr the particles. and the water Ievcl is

li kept more than 30 cm below gr:rvel‘mulchcs, chapter 9). Rc , d

the surt’ace to shield it from evaporation (see cntly, two small. plastic-lined tanks were built

near Sufford, Arizona, and Qilleh by commercial rot rocks rcduccd the tank’s volime by 55 percent. but tl

icking machines. The

/ -I’ reduced evaporation by 90 percent.j’ Another @ated technology is the sand-filled water storage tank developed in the Sudan fo/cbuse with rainwater harvesting (FIGURE 1 1).

Small sand-filled dams hav.6 been used in the Nan-rib Desert since 1907 for h ” k. supplying drinking water ,td’livestock. They can store water for long periods,

“~qnuch longer than conventional open storage. They can provide water during -. ‘X. ,’ I 31 &3X3~~~a1. 1972. (See Selected Readings.)

.-

The clam wall is built aCross tllc riverbed duri,lg the dry season; later. the river bloods will deposit the necessary sand and &~vel. Norm;l]]y, the soil carried by Ilood waters is 3/4 sediment and:,mud and only l/4 sand and gravel. A ,dam trapping all of this mkture would quickly silt up. To ensure that only sand and gravel are deposited, the dum wall is heightened in stages or wanly, I III (ll1ougl1 tllc first is usually about 7 111). Flqodwaters deposit heavy glavels~mcl sand, but silt and soil arc c:lrricd over lhc top by llic specd- ing waters. I.~~li l-m stage is aclcl$ when t I1c clam is tilled wi 111 sand an~f gravel (which may rcquirc a complete wet season) until the operating height of 6- 10 m is reachccl.

Sand dalns ar& articularly effective wJ!en built c)vcr fissurds that lead underground to natu

\

1 aquifers, for the dam cm slow rushing floodwaters enough to get the aquifer -acharged (chapter 16).

A simplified approach to this method is to use a pump and a well-shaft system that can be readily sun\!into dry riverbeds’to extract water stored naturally in the sand a few feet b;low the surface.33 \

i;,!

: . 32Wipplingcr. 1958. (Set Selected Readings.) 33Ba11 and van Rynvcld. 1972. (See Selected Readings.)

D

.;t 0

MORE WATER FOR A.RID iANDS

FIGURE 45 Sand dam in South-West Africa built of rock and mortar. (0. Wipplinger) e

Advantages

Evaporation control is, a particularly important way to conserve water because it usually requires little ,new construction and the additional water becomes available without construction delays. In many cases it will cost less to reduce evaporation than to collect and store an equivalent amount of water from other sources. Some of the better materials have provided wate”r for less than U.S.$O.O25 per m3 in a 200-cm-per-year evaporation zone3 ’

Evaporation is greatest during the driest seasons, which are also the peak periods for water use. Controlling’#only dry-season evaporation with short- lived methods could have economic significance in arid lands.

Suppressing evaporation in impounded waters also suppresses the increase *’ in salt concentration that occurs with evaporation. Floating evaporation- control materials cut off the light, thereby reducing the growth of undesirable algae and submersed aquatic weeds.

Limitations

At present, evaporation suppression is limited to small storage facilities such as ponds, tanks, troughs, and oases. In practical terms large reservoirs,

31 Cluff, yt al. 1972. (See Selected Readings.) ‘sp n

’

REDUCING I;:VAPORATIONI~ROM WATER 79

lakes, and rivers are still beyond the reach of available technology because it is very difficult for the evaporation-suppressing system to survive heavy winds, storms, and floods.

The effects of evaporation-control, methods on animal life in the water may not be important in small containers. but they should be considered in reservoirs.

Sand storage dams can be built only where the geology permits. The floodwaters IIILIS~ contain gravel and sand (coarse or fine granite, quartzite, microschist, anh 1 c une sand all work well), and the dam site must be made absolutely watertight (c.g., cement-grouted to stop seepage if ncccssary). To build a sand dam requires patience, time, and logistics that can cope with delays while each stagc’of the dam wall is built, because often only one stage

.,can be added each year. For this last reason the tcchnolog~ has not yet been widely accepted.

Seepage control (chapter 8) is usually easier and cheaper than evaporation control;’ therefore, evaporation control should not be considered for a reservoir or water-distribution system until seepage is controlled. ‘...

Stage of DevelopmeFt

Ilydrologists and engineers have long been aware of the quantity of water in arid lands lost each year by evaporat+n, but evaporaiion suppression iS still experimental. By far the greatest number of studies have been concerned with alcohol films. Although research conducted on the use of‘ solid tloating materials is limited, progress has been’ considerable. This method appears to offer the most promise for small storages. Sand dams have been built by the score in South-We.st Africa during the past 50 years. A few have also been built in Kenya arId other countries of East Africa.

Needed Research and Development L

No economical method exists for reducing evuporu tiun fron multipurpose reservoirs; research in this area is despara tely needed.

.I large,

Extended field trials are needed to test the practicality of the floating -, ‘!

covers, such as expanded-polystyrene rafts or wax layers on water reservoirs. These do not require any special equipment or skills and can b readily

’ introduced into arid lands for pilot testing. s .

Research is needed to overcome the mechanical difficulties of stabilizing any evaporation-c,ontrol system on water surfaces subject to wind, wave: and currents. This is particularly so for the alcohol monolayers. : . .

It is likely that some radica!ly different a~pro~chcs io cvaporatlon control await discovery; research into no,vel methods is encouraged.

The sand s vrage dam is a technology’ihat needs field testing in man>~ arid areas. Research is needed into’its rational design: c.g., for the height 01‘ stages I II in relation 10 the extent of the catchment.

Selected Readings

Contacts

General

Dcplrlrncnl of Agricultur:ll I~ngincering, Oklahoma Stdfc‘ Lnivzrsiry. Stlllw;itcr. Okla- homa 74074, -LISA (I.‘. I<. (‘row)

11

Sand Storage Dams 1

Department of Civil Engineering, University of Stellenbosch. Stellenhosch. South Africa (0. Wipplinger) I

Department uf Conservation and L&tension, Causeway, Salkbury, Rhodesia (1’. S. Ball)

Ministry of Agiculture. P.O. Box 8108.

Ilydrnulic Rcsc;lrch Laboratory, C.S.I.R., P.O. Ho\ 395. Pretoria 01. South Ainca Illinois Stat$‘W;ltcr Survey, Urban;\, Illinois 6 180 I, USA (‘v$‘: J. Roberts)

ucing Seepage Losses

rcscrvo1rs. 13ccauso lhcir soils arc often porous. illail)’ ()I”, thcw storage i‘acilitics and conduits sul‘fcr serious water Iosscs tliroil$l sccpagc II1 dlvcr tlng water I‘rom its intcndcd purpose. seepage call also C;IUSC scrlous \v;itcrlogglng. salinification, and erosion of‘ neighboring ~11s.

Sccpagc UJI bc reduced if‘ the walls 01‘ rcscrvolrs and s~~nduits’arc’ made watcrt ight. I<cccl~lt tccllnology hris produced manv illcslwnslvc’, n’;ltc‘rI>roc11 materials that ~nay prove valuable for tl11s purpose.

01‘ tlic various ways.to rcducc scclxlgc. 011lv some 01‘ the iicwc‘r. low~ost _ met<kxls arc discussed in tllis report.

Methods

Maiiy ways to make soils impervious l’or rainwater liarvcsllng (sot l~sr III chapter I ) can also bc used to rcducc seepage III watcrwa\‘s so11 compactIc)II, chemical trcatmcnt of soil. and soil covers sucli as butyl rubber. sheet plastic, asphalt rcinforccd with plastio or fiberglass; and ferrocement.3J

Much sccpagc is caused by calcium in the soil. Calcium causes clay to bunch up (aggregate), forming cracks and a porous structure’that lets water :

lsccp through easily. In this situation seepage can be greatly ,..rcduced b> “.,...- trcatlrlgl-l-x soil with a sodium salt such as sodium carbonate (FIGURE 46). Sodium brca&%p clay aggrcgatcs (FlGURE 47) and c‘ausc’s clay particles to swell and plug the $01 -put> (FIGURE 48). This method C;IJI bc s~~cccssl‘~~I Y

only whcro conditions arc l‘nvok&.k (e.g.. the soil must have 3 minimum ot’ I5 pcrzcnt clay, bc at Icast 30 cm deep, and have the chcmicul capacity to exchange calcium for sodium ,ions.) “.

Shallow carthcn, but rock-free reservoirs (less than 3 m dselj) car1 be made watertight with low-cost polyethylene and polypropylene films. but deeper reservoirs or those built on stony soils require thicker and rougher films of vinyl or reinforced polypropylene. In both cases the films should be

3,4Sw, for example, Ferrocemenr: Applications in Developing Countries. (Available without ChilrgC. See publication S, p. 152.)

FIGURE 46 Cracked soil structure indicates high calcium content in a dry pond bed in Coconino National Forest, Arizona, USA. Water seeps away through the cracks; original” seepage loss in this 1,000 mz stock-watering pond was 5-l 2 cm per, day. The dfy pond was cleared of rocks and weeds and 1 ton (about USSSO worth) of sodium carbonate applied by hand. This was then mixed with the soil io a depth of about 8 cn;,with a small tractor and disk, and

prutcct~d with a’covcring ol‘ soil or gravel. In Europe I-l’nd the Unlted States butyl ru\,bcr is incrcasing!y used tu lint rcsc’woirs. wtcr cha~~~~l~. and storage tanks. h is strong. durable, wcatllcr and pest prl~l‘, but it 1s an expensive way to reduce scepxgr. .*

Concrete-based materials, such as cen;entzstabilized soil. ferrocement. and concrete-tilled fabric also haye potential. . \

One problem en%ountered in lining reservoirs is stabilizing the banks. Soil * is usually unstable on slopes greater than 1 :3: Steeper slope2 are‘d&rable. however, to maximize storage, minimize evaporation losses, and inhibit ’ weeds. Promising methods of providing a rcvctmcnt to protect steep bunks

’ include the use 01‘ used rubber tircs.“t;?‘rrocc‘mc‘r~t, and soil cement pac’icd into sausage-sll;lpctl plastic bags (.‘FIGURES IO- 12. pp: I?-20). Near-Frtical slopes ,. can be constructtid with sausage revetments. Local soil is blended with a small ’

~_n amount ‘01‘ cement and moistcncd through pinholes made in the plastic tube. The sausages are stacked in place tightly and all&ed to set.3s This technique is also suitable for canal and ditch revetments.

Advantages ‘- I.. -4

Any reduction in seepage provides additional water without requiring new ’ T equipment or,,f‘acilities, and most methods do not interfere lvith use of the

3s1ntern>cdiate k’echnology Development Group, Ltd. 1969. (See Selected Readings.) I

r ‘. 7

MORE WATER FOR ARID LANDS

FIGUR;‘48 . . . \

Seepage then&opped to 0.4 cm per day. AfIer a’ “booster shot” of ‘. 200 kg of‘sodium salts .(33 months after the i&i&l treatment) this low seepage rate has

beenmaintained in the pond for 5 years. (U.S. Department of Agriculture)

impoundment for recreation, fishing, etc. In some areas reducing seepage prevents associated problems such \s waterlogging and salinification of the surrounding soil. Lining canals ,als& reduces maintenance and weed-control problems. 3 6 ! ’ Iri, general, reducing seep:ge in, reservoirs, and conduits iseasier and ,j . more economical than reducing evap ration losses (chapter 7). \- 1 Lirhitations ; ’ r \ A,.; e

“: b

1 The primary disadvantage of seepage control is its cost. ’ In most methods maintenence of the lining is a constant concern

,becausE even small holes can allow large amounts of’water to drain away, ’ ‘1

. especially if the*surrounding soil is porous. 3 * i

36For a discussion df aquatic weed pro,blems see publication.1 lx-, p. 153 / >

- REDUCING SEEPAGE 85 - /

. . Stage of Development ,

Seepage control has been practiced in arid lands since the beginnings of civilization. However, most of the techniques discussed in this chapter-

- including -the use of sodium salts> plastic sheeting, and butyl rubber-kave been used within the last 20 years and are commercially available. Reinforced asphalt has been under test for approximately 10 years. The use of in’expensive polyprop’4;lene is a recent development, not yet extensively tested

d or utilized. Ferrocement, virtually untested for this purpose but known to be wateriight,, holds great promise because it can be constructed by uriskilled labor using materials available in developing countries.

Needed Resbarc h and Development

There is a major need for widespread field trials, particularly in arid developing. countries, to test and compare the effectiveness of d;ffere^nt

.- systems and consider the economics‘of their application. New, more economical r$tterials are needed, fo.r they could make seepage

control possible worldwide. As new watertight membrape materials becolvi: +.,;available, their use in this application should be evaluated. I

lmprovemen ts’ in sealing and laying undirground moisture barriers (chapter 12) could bring major breakthroughs; a watertight seal could be laid directly in the soil where it is protected from mechanical damage and weathe.ring.

Selected Readings

Board on Science and Technology for International Development. 1973. Ferrocement. Applications in Delleloping Countries. National *Academy of Sciences. Washingtpn, ‘I/ D.C. (See publication 8, p. 152.)

Boyer, D. G., and C. B. Cluff. 1973. An evaluation of current practices in seepage control. Hydrplogy and Water -Re@ources ill Arizotla atrd ClJatcr Resources in Arizona and the Solghwest 2: 125-51. Arizona Section of the Amertcan Water Resources Association, ‘Tucson, Arizona. (C”omplete volume available from Water Resources

,i Research Center, University of Arizona, Tucson, Arizona 85721. USA.) Intermediate TeqhrI6lGgy Development Group, Ltd. 1969. The I,ltrodltction of ’

Rainwater Catchme)l) Tanks’ and Micro-irrigatiolz to Botm~ana. 74 p. (For ITDG , add.ress, see Contacts.)

Kraatz, D. B. 1971. Irrigation canal lining. Irrigation and Drainage Paper Number 2. Water Resources and Development Service, FAO, Rome. 170 p.

Myers, L. E., ed. 1963. Seepage Symposium, Phoenix, Arizona, Proceedings. Agricultural Research Service Report A.R.S. 41-90. U.S. Department of Agriculture, Washington. D.$, USA. 180 p.

n Reginato, R. J.; L. E. Myers; and R.‘S. Nakayama. 1968. Sodium Carbonate for Redu,cing Seepage from Ponds. Report Number 7, U.S. Water Conservation Labora- tory, A.R.S., U.S. Department of.Agriculture, Phoenix, Arizona, USA. 6 p.

e .-’ . ^‘. ,

“$ * . MOR.E WATER FOR ARID LANDS

‘\ -. . ,A.

&Stfcond Seepage Symposium,’ Phoenix, Arizona, Proc&dings. 1968. Agricultural Re- 7;T‘ search Service, .Report Number A.R.S. 41-147. U.S. Department of Ag&Mure,

Washington, DC., USA. 150 p.’ The University of Arizona, Cooperative Extension Service and Agricultural Experiment

Station. 1965. HOW to Make a Plastered Concrete Water-Storage Tank. “Bulletin A-41.. Tucson, Arizona, USA. 12 p.

% Co&s . . . Plastics (and agricultural) supply houses .in some countries should have in stock

materials suitable for lining ponds and conduits. Some agricultural supply houses also carry sodium and phosphate salts for pond sealing. The‘Tollowing are involved in research developments: I Bamangwato Developmept.Association, Radisele, Botswana

:, Doxiadis Ionidcs Associates, Ltd., Ripley, Surrey, England Intermediate Technology Development Group, Ltd., Parnell House, 25 Wilton Road,

Loffdon SWlV 1 JS, England Water Resources ar@Qevelopment Service, Land and Water Develapment Division, Foo / 7

P and Agriculture Oiganization of the United Nations, Via delle Terme di Cara a, OOlOc); Rome, Italy ,/y

Water Resources Research Center, University of Arizona, Tucson, Arizona 85721, USA ’ (C. B. Cluff) ,/’ ,’

. i

B

atio aces \ _- ;

Evaporation from soil surfaces wastes large amounts of water-an important consideration in arid lands where low humidity greatly encourages evaporation. From one-fourth to one-half of the water iost from a crop is evaporated from the soil surface. 3 7

This loss can be reduced and ircgation water saved by placing watertight moisture barriers or waler-retardant mulches on the soil surface. 38 In many cases these barriers will also stabilize loose soils, stop-desert encroachment, allow runoff agriculture,. aid in landscaping, or reduce salinity buildup. ..-

Suppressing evaporation from the soil conserves water where its effect is great: within the root zone of the plant. III an arid region small water savings

’ here may be more important to a crop’s survival than large improvements at earlier points in the water supply.

Methods >

Some soil-surface moi

A

re barriers are made of nonporous materials such as paper, asphalt, I 011. plastic film, or metal foil. but a 5-25 mm thick layer of por’c~us material can also substantially reduce evaporation. Water and water vapor move so slowly through a dry, porous material that soil moisture is retained. In practice, suitable porous materials are plant residues such as straw, sawdust, wood bark, or cotton burs, as,well as gravel, sand. or cinders.’

Plant Residues

Planting directly into the standing residue of the previous crop is one way to ‘retard evaporation (and reduce erosion) because the residues and hard soil

1 surface provide a better moisture barrier than the loose surface left after

37Viets. 1366. p. 270. (See Selected Readings.) 38Also by creating windbreaks of tre.es, fences, or taller growing plan&-a well-known

and highly site-specific method not dealt with in this report. (see also FIGURE 50)

87


ploughing. This is known as minimum tillage (FIGU& 49). Because weeds that would normally be buried by the plough become more of a problem with this method, stringent weed control (with herbicides or hand labor, but not methods that destroy the soil surface) is essential for its success. Sometimes the soil surface may have hardened enough to retard all water penetratiozand chiseling may be necessary to get enough moisture to the root zone. r

Plant residues such as straw and cotton burs spread on the soil also retard evaporation. Water and soil conservation is greatest when the resid,ues cover 90 percent or more of the soil surface. The amount of crop residue needed for this is about 1.5 tons/ha in the case of straw and 1 1 tons/ha for cotton burs. For residues. spread on the soil surface, the greatest reduction in evaporation comes with the first 5 mm of thickness.

Gravel Mulches

Infiltration of water into soil and the conservation of soil moisture are, greatly improved by gravel mulches, even in layers as thin as 5 - 10 mm. They

B FIGURE 49 Minimum tillage in Texas, USA, Grain sorghum is planted on both sides of row of cotton stalks. After sorghum is harvested, new cotton will be planted between the rows of sorghum stubble. (U.S. Department of Agriculture)

. .B _

”

REDUCING EVAPORATION I:ROM SOllo $‘I

reduce erosion by wind and water; if light colored, they cool and if dark colored, they warm the soil. Either in the right environment can benefit plant growth.m

The chief problems are cost, the need to periodically redeposit the gravel on the surface, and interference with mech’anized planting and cultivation. A machine developed ‘to Jay gravel-covered plastic catchments (chapter 1 ) can be used to separate the gravel and lay it on top of the Soil as it pas&.

I In arid Lanzarotte, in the Canary Islands, black volcanic xl1 IS qu:ir;rcd 1 q-d spread -over ficl& of vegetables and grapes and scrvcs’as ;III cscell~nt “-&;“poration supprcssan’t (FIGURE SO).

r

Paper and Plastic Mulches -*

Paper and polyethylene plastic mulches arc now widely usc;d ,to contI;cA weeds, increase soil temperature, and speed up.plant germination and growth.

* Their use specifically to retard evaporation in arid regions is now being researched‘ (FIGURES 5 1 and 52). Yields of irrigated corn per unit of‘ water evaporated and transpired have been nearly doubled in OIIC cspcrimcnt whcrc . the soil was covcrcd with plastic film, indicating that up t[, hall‘ the w;~,tc’r used by unmulchcd corn may be lost through cvapo,r;rtion from the soil

\

surface.39

Latex, Asphalt, or Oil Mulches

Latex, asphalt, and oil have been tested III specific dcscrt sit&trons I.OI their ability to cpnscrvc soil moisture, to conce.ntrate rainl‘;lll (by, &eating runoff), and to suppress the movemept of wind-driven sand long enough for plants to get estabiished.

These mulches have been used commercially to establish vegetation on water-bearing sand dunes in, for c rampIe. Libya, India. and Australia (FIGURES 53-55). By retaining the heat qjxuqbcd during the day, they can

YC

keep desert soils warin during cool nights. This incrC;rscs the ctlan<c> 01‘ survival for plan ti whose roots must othcrwisc withstand Iurge dally temperature fluctuations,

-I

Pther Chernicais’ ,

I Silicones, polyethylene oxides, pblysaccharide gum mixtures, fatty alcohols, and cationic, anionic, and nonionic chemicals have been tested as evaporation suppressants without much success. ,

3gDoss, et al. 1970. (See Selected Readings.)

.

I .-

. Advantages

m

’ a The major advantages of mulches are that they conserve moisture. reduce n wind and water erosion, and increase crop’ yields, especially in dry years. Mulches that increase soil temperature (plastics, asphalt. oil, dark-colored y gravels and rocks) hasten germination and seedling growth in regions where soirs are cold at planting time. Mulches can improve the quality of some fruits by prcvcnting their contact with the soil. Plastic and petroleum mulches can be used to collect runoff water in ‘depressions around plants, making ;I form of runoff~agriculturc.(Fl~URE 52).

- Limitations

For most mulches, the prime limittition is cost. Treating soil with chemicals or coverings it with plastic sheets is not cheap. Today, these treatments are suitable only for intensive agriculture of high-inqome crops such as pineapple and strawberries, or where a complemen<ary feature such as stabilizini sand dunes adds significant economic benefits. The costs of

92 8 MORE WATER I’OR ARID LANDS

.

FIGURE 52 These plastic “aprons” are being evaiuated to determine their ability to catch rainfall (chapter 2), reduce evaporation, suppress lveeds, and promote the growth of tree seedlings in arid areas. (FAO)

i;

REDUCING lI.VAPOR.ATION FROM SOIL 93

FIGURE 53 Stabilizing dunes with a heavy oil mulch in the. Rajasthan Desert. India. This process was first applied in Libya to 160 ha of bleak, barren stretches of the Sahara Desert (see also FIGURE 5’5). The dunes contained mo&ure 0.5 m below the surface. After treatment they were planted with 60,000 eucal’ypttib trees; 90 percent survived the planting and continued to grow. One, m high~,whcn plant&l, they grew to over 2 m during the first year. Unstabilized sand would either bury the young plants o”r blow away. csposing Lhcir roots. (ITsson)

/ chemical; and plastic mulching. may also bc justil‘icd in locations wlwrc soil

, erosion can be inhibited. Prices are affected by c

o Availability of ingredients (e.g., lates, oil, water); o Topography of the area to be treated, its 6rtilizer needs. and the

amount of preparation;‘such as leveling, required; e Availability of suitable machinery and personnel for both preparing and

treating.Jhe area; and ’ e Type of vegetation to be planted. L The main disadvantage of plant residlles as mulches is their relatively sl-!ort

lifetime. They are also difficult to keep in place in windy weather. Plastics, on

_

94 MORE’WAXR FOR ARlD LANDS

FIGURE, 54 Consistency of and stabilized with an oil/latex mulch. Sealed surface reduces evaporation losses nnd holds the sand in place Ions enough for plants to become established. (International Synthetic Rubber Company, Ltd.) _1

.

the other hand, deteriorate slowly and may interfere with the planting of subsec~ucnt_clops. Gravel and rock mulches are not moved by wind, and they allow rainfall psnetration. -But they may be espcnsivc to install and can intcrfkre with tillage operations.


Mulching with rock, gravel, and crop residues are age-old methods for conserving soil moisture; nevertheless, their worldwide potential today is not fully appreciated. Minimum-tillage agriculture has only recently bee,p widely appreciated as a desirable agricultural practice. The nonporous mulches-

ci plastic, paper, oil, asphalt, -and latex--have all been made, possible by ,

I~IC;URI~~ 55 l‘wu ycal’s al‘t~1r trcatrnont as in FIGURli 54, eucalyptus trees, 0.5 m tall when pI;u~~cd, h;~vc #wwn to 1 .S-3 III. In the Libyan dcscrt mulches prorcct thousands 01 hcct:ws 01’ I‘rcshly plantctl young trees t’rum encroaching sand. (Intcrnat~unal Synthctlc Rubbrr (‘~~rnp~~y, Ltd.)

.Needed ResearcRand Development

The main need is to develop mulches specifically for arid developing countries, particularly mulches that maximize the use of local resources, Arid-land studies on ~hc hllgwing arc ~ilso needed:

Thickness 01‘ rnulcl~~ Potential toxicity lo plints and soil c)rg;IIilsms Alterations oI’ the nlicrocrlviro~ln~cllt by tillage c)pcr;ltions Improvcmcn t ol‘equipmcnt to gcncratc and maintain gravel mulch

S,elected Readings

, Adams, .I. I,;. 1970. Effect of,mulches and bed configuration. II. Soil temperature and growth and yield responses of ~ cyrain sorghum .und corn. .-igronom~~~ Journal 62:785-90. s’

Arnon, I. 1972. Cro[~ Producriorl ii1 DrJ, Regions. 1’01. 1 Backgroutld and Principles. Barnes and Noble. Nc\v York, and Leonard Hill Books, London. 650 p,

Doss, B. D.; c‘. C‘. King; and R. nl. Patterson. 1910. Yield components and water use by silagc corn with irrigation, plastic mulch, nitrogen fertilization. and plant spacing. &W~JUl~,’ JrJrmlu/ 6 2: 54 I-3.

MORE WATER I-OR ARID LkmDS

Fairbourn. M. L., and C. 13. Cluff. 1974. Use grav~~mulch to saw water for crops. c’rops ntd Soils hlugazitle April-May 1974. . .

Gonzales, B. Il., et al. ‘.‘,?I Mulcl~” en 10s Cuitivos Etlatmado~ de Catlarias. Instituto de Hidrologia, Centro de Estudios Hidrograficos, Comite Espanol de Riegos y Drenajes, Madrid, Spain.

Greb, B. W. 1966. Effect of surface-applied wheat straw on soil water losses b>, solar distillation. Soil Scierlcc Society of Atnerica Proceedit~gs 30:786-8.

IHanks, R. J., and N. P. Woodruff. 1958. Influence of wind on \vatcr vapor transfer through soil, gravel, and straw mulches. Soil Scicr~c& 86: 160-64.

Koshi, 1’. ‘f., i11111 D. W. I:ryrcur. 1971. Ilffcct of.sccdbcd configuration‘ and cotton bur n~ulch on lint cotton yield, soil water, and water use. A,qotwrny Jo~rnla/ 63:s 17-22.

Kowsar, A.; I:. Bocrsnw; and G.d D. Jarman. 1969. liffccts of pctrolcum mulch on soil water cuntcn( and soil +cmlx:raturc. Soil Sciertw S0cic~r.b~ 0/ .4 ttlcricu Procc*cditigs 33:783-6.

Lippcrt. L. I-.; 1:. I-I. Takatori; and 1,‘. L. Whiting. 1964. Soil molsturc unclcr bands ul pclrolculn ancl polyctliylcnc rnulchcs. /l~?fcrrc@rr Socic~l.~~ jbr I~c~r[iclrllumi Scic~trcc .lorirttal 85 ~54 1 .

Papcndick, 1~. I.; M. J. Lindstrom; and V. L. Cochran. 1973. Soil mulch cffccts on ’ sccdbcd tcmpuraturcs and water during fallow in I;x,tcrn Washington. Soil Sricr~cc Society) oj’fi twricon Procwditip 37 :307-l 4.’

Viels, 1;‘. G., Jr. 1966. Increasing water use cfticicncy by scjil management. In Ylorrf i:‘t~vi,ot~ttrc~trr arrtf /</:/~~‘~L*III IVurlrr list. Am3ric‘;ln Society of Agronomy. and Soil Scicncc. 677 S~iutli Scgoc Rwd. !vl:idison. Wisconsin 537 1 I , USA.

* b / I

Contacts

Agricultur;ll antI Irrigation I<ngincc~ring Dcpartmcnt, 111x11 SI:IIC Univcrslly, Logan. Utah 84321, USA (17. J. Ilanks)

.

Agrlculturc l)lvision, ARAMC’O, Dhahr:in. Saudi hr;ibi;i (S. L3bbxn) I)cp;irl nicnl 01‘ Agronomy, (‘ollcgc of Agrlcullur:ll Scicnccs. ‘Tcx3.s l‘cch Univcrslty.

Lubbock, 'l‘cs;is 79409, USA (II, 1:. Drcgnc) . Dcpartmcrlt c)l‘ llorticulturc, Univ~r~lt)’ of 1111wi1~. llr\xinn, Ill1n01\ h I SO 1, liS:\

(I-I. .I. Ilo}lcll)

Depart nlcnt of Ilorticulturc and LandscApe Architccturc. Univcrsit!, of Arizona. Tucson. Arizona 8.572 1, U’SA (N. R. Ocbkcr) I

Great Plains I:‘icld Station, U.S. Department of Agriculture. Agricultural Research/ Service, Mandun, North Dakota 58554. USA (X’. Wiilis) a 1

Ministry of Agriculture, Tripoli, Libya (hl. Thahny) U.S. Dcpart!nont 01‘ Agriculture, Southwestern Grcut Plains Research Ccntcr. Agricul-

Iural Rcscarch Scrvicc, Busl~lnntl. Tcsas 7901 2, USA (1~. D. Stc\varl) \V:itcr Rcsourccs and Dcrvclc~plncnl Scrvicc, Land :rntl Waler Dcvclopmcnt Division. I-ood

and Agriculture Orguniznlion of 11~ Unitccl Nations, Vi:t cicllc Tcrmr dl C:lr:ic:ill;t, WJ loo, I~OIll~, Italy

c

‘10 Trickle Irrigation

St:~ild;~i~d irrigation rncthods ;1rc p~~rt~cul;irly wasrcl‘ul 01’ w’atc*r III arld I;111ds bccausc the cxtcndcd :1rc;1s of’ wcttcd soil greatly ciic‘ouragc c’vaporar~vn (chuptcr 9). A newly dcvclopcd irrigation system, liii~~wri 3s “drip” 01

“trickle” irrigation, uses a system 01‘ plastic pipes plnccd mloiig rhc plnnrs 011 or under the soil (FIGURES 56. 57). Water carried in the plpcs drips onto the soil thyough outlets arranged near each plant (FIGURE 5s); bccausc only ;I small rumuti1 n 1 111 soil is watered. cvnporation losses xc minirnticd. ‘Furtllcrmorc, the rate ‘and time ,01‘. w:ltcr’ aPl’licatio,;~;~~c ;ldjujtcd t‘vr no runtrl’i‘and minimal deep percolation losses.

FIGURE 56 Trickle irrigation, showing the areas ivetted by individual drippers attached to the plastic pipes. (S. Davis)

, 9 7

F

.- FLGURE 57 Trickle irrigation sysTem in ChliI‘ornia, cmittcrs bcsidc the trees. (F.;K. Aljibury)

USA. 1’iFs letid the water tu

f

FIGURE 58 Trickle emitter dripping irrigation water. (F. I(. Aljibury) i . .

.; .-’

TRICKLE IRRIGATION

Method

_, 99’

In .trickle irrigation small amounts of water are applied at frequent . 0 interval; to a specific site near each plant. under each site a wet area is formed, that extends to the plant’s roots. The applicatiod can be adjusted to replace water continually as it is used up by the plant. To co Iserve energy and minimize lldw rates, trickle-irrigation systems a’re no\mall operated at relatively low pressures (1-3 atmospheres).

Basic cquipmcnt for trickle irrigation consists of a i 1 wa cr-s, pply head. a

’ I, n’lgin. delivery pipes, manifolds, lateral hose lines. and en,itters. The head,

between the main water source and the pipeline network. u\ually consists of .._

control, .valves, couplings, fillers, screws, timcclocks, fcr\$ilizcr injectors, gauges, etc. Since the water passes through very small outlels in the cmittcrs, it is screened, filtered, or both before it is distributed in the pipe system.

n

Advantages

Trickle irrigation is replacing surface’ irrigation in some arcas $ere: ’ + Water is scarce or expensive, a The soil is too porous or too impervious for gravity (flood or furrow)

irrigation, a‘ Land leveling is impossible or very costly: / * Water quality is poor, l It is too windy for sprinkle irrigation, l Trained irrigation labor is not available, or b . Irrigation labor is expensive. Trickle irrigation not only improves the efficiency of water use but also

@es much greater control over the placement and amount of water. The amount of qYater can be adjusted to the soil’s absorptive capacity and to the ‘characteristics of the particular crop, its stage of growth, and the climatic

,‘conditions. Thus, unlike other irrigation methods, trickle irrigation minimizes surface standing water, which can breed mosquitoes and incrcasc watcr- logging and anaerobic soil conditions that advcrscly affect plant growth.

Trickle-irrigation equipme@ costs must be judged in light $f the cspensivc land preparation (and contivued land maintenance) often required by surface irrigation. Land leveling, and canal and ldrain digging, reqeheay equipment, skilled operators, and a .consi&rable infrastructure: all are dis!pensed with in a trickle-irrigation system?The potential cost savings are large.

Fertilizers can be applied through the trickle system and efficiently applied close to the roots. Fertilizing through the trickle system generally promotes better plant growth response; the timing ‘and number of applications required, however, are still uncertain and undgr study.

i:t

ic

ER I-OR ARID LXNIIS

pipes for trickle irrigation, using water froin a brackish geothermal Unlike other irrigation methods. this one can easily keep

pipes. %rm water heats tht’ soil, stimulating plant growth oldness of thr dcscrt night. (J. Schcctcr)

0

. _ a

0 *i,

TRICKLI: IRRIC;ATION ‘t 101

Because tde irrigation water never touches the leaves..johar salt damage is ’ not a hazard with trickle irrigatidn. Provided the mechanisms of water and d salt distribut-ion in the soil are adequate, trickle irrigation.may be a suitable - way to use poor-quaiity irrigation water (e.g., salink waters up to 2,500 mg of salt per 1; see chap& 3 and FIGURE 59).

Many moisture-induced leaf and stem diseas s (e.g., fungal dis6&es) fostered by other methods of irrigation ii are:.mi imizcd or dcl%atcd b> trickle irrigation, which’ may also help’ control p~thogcns7that devglop in watcrloggcd soils. c

Bccausc trickle-irrigation water drips onto the soil withdut disturbing the surl‘acc, soil erosion and surface crustation, which impcdc water pcnctration, I. are usually climinaicd.

,a e ,..-a

P

Limitations *

.--’ To deiign, install, and operate a trickle-irrigation system, skills different from those for other systems, arc necdcd. Pbtcntial users. unfamilrar with the technology, are urged to corisult with specialists to identify the best,.d&ign for their arca. Unfortunately, numerous’unproved claims for such systems have been made by aggressive promoters.; all claimi should be carefully studic and imalyzcd. a

2

:

H-i rickle irrigation has proved most effective for pcrmunent tree and vine crops, and\-or crops grown totally under cover (chapter 15). In many standard situations, however, it may be less appropriate than conventional

I methods. There” are some serious technical problems with. trickle irrigation.. The

primary problem is clogging of the emitters by: + . .C Prscipitates from liFestone-containing waters

Prccipitatcs from irsn-containing w J \

s Algae .

. Suspended silt, clay, or fine sand Some clog&ng problems can be eliminated by carclul rnanagemi:nt,

filtration, and $emical treatmerit, but this increases operating costs. At present,. trickle irrigation cannot be used with iron-containing water. Algae are’*normally removed by chemical treatment fbllowed by filtration. Methods for renioviiig fine sand, silt, and clay are still inadequate, especially where large amounts of suspended materialCare encounterep. In addition, careful controll during construction and maintenance sential. to stop particles entering the system.

With trickle irrigatio? as with other methods. careful management and expert advice are essential ,when saline waters are used. This is especially true

’

. -

- 102. . ’ MORE WATER FOR ARID LANDS q

’ in arid areas b&use evaporation can cause surface,accumulations of salts that damage. crops when *rains wash them-down into the root zone. Furthermore, ” insufficient water for leaching (chapter 3) can result in salt buildup deep in the root zone. Althsugh the sa&rization hazards of trickle irrigation remain to be quantified, they seem to be less t&an with other irrigation methods.

Trickle irrigation requires precise equipment which, though available, has not undergone long-Term application. Particularly important in this respect are’the emitters and filtration systems.

S&e of Development ’ 0

The commercial use of trickle irrigation is ratidly increasing. An cstimatcd 15,000 ha arc under trickle irrigation in Europe,*. with an increase of 25 percent or more each year. California’s trickle-itrigation acreage was 60 ha in 1970, $0 ha in 1971, 8,000 ha in 1972, and approximately 16,000 ha‘in 1973. It is used mainly for permanent crops such as avocados, strawberries, tomatocsl (FIGURE 60), citrus, nuts trees, and line-wine grapes, grown either

\ d 0

a ‘T

FIGURE 60 Trickl~&riga,~d tomatoes on a 500-ltti ;cgetdhle :lnd fruit t‘arrn near Dakar, Senegal. Although hqh, the cost is offset by an estimated 3040 percent savings in water over other irrigatidn methods, -fewer weeds (saving tirnt and labor), easier disease control, ati easier agess betwm rows. Fertilizers are injected into the trickle system, saving much of the usqal application expense. (Bud Senegal) s

/ /

I 1

in soils where water/ pengtration is very slow or in highly porous soils whe’re :it is very high. ._ _ - I .I

Development of itrickle irrigation .1&s &r behind that of ather irrigation - methods, including 1 spri&ler, irrigation. Although it- is considered a new

method, the &basic cbqcepts of trickle ir’;igation have been used since the early 1900s by nurseries &owing fruie trees and ornamental plaizts. -y-.. > I 7 ,I-’ - I

i =

Needed’Reseakh &nd De&loprnkt <

are available, but improvemevts in design are neecled td $ crf ,en&tter plugging. Self-cleaning emitters: ’

proved in long-term use. The problem is to - filters than can remove extremely fine,,

y, silt, and algq particles. As y+;>o filter screen or eet the desired service requirements. ‘7.1

a

ones that rodents

or flow-regulating devices to offset pressure variations lue to topography or ipe friction that cause different drip rates throughout

be learnzd about trickle/irrigation and its effects on pread field tests .of th,e trickle. method are needed on:

nematocides, fungicides, \etc.;tJuough the trickle system; and ‘---.&-The’salinization hizards of trickle iriigation. ci

” L -- ..___ c \ ;-- --_~_ Selected Readings ’ ~--~ -- ~-_---- .- _ I

Aljibury, F. K. 1973. Drip ir&ation; practices and applications.. Cahfonria Farmer,238 (12):‘28 a, b, c.

’ Bernstein, L., and L. ‘E. Francois. 1973. Comparisons of drip, fumow-and sprinkler irrigation. SoilScience, 115(1):73-86.

European Comniissibn on Agri$ulture, Working Party on Water Resources and Irrigation. 1973. Trickle Irritation. Irngatidn+nd drain Development Service, FAO,Rome. I53 p.

e paper MO. 14. V@er ResourceS%nd


Karmcli, D., and J. Keller: 1974. Tn’ckle Inigarion Des&r,, Rain Bird Sprinkler ‘Corporation, Glendora, California, USA. 120 p. t In press.)

Keller, J., and D. Karmeli. 1974. Trickle irrigation design parameters. Transactions of the c American Society of Agricultural Engineers. (In press.)

Contacts

Many ‘companies around the world are now beginning to market equipm,Bt for trickle irrigation. Local departments of agriculture or agricultural extension %-vices should have pertinent information. The following are monitoring research developments:

Agricultural end Irrigation Engineering Department. Utah State University, Logan, Utah 84321, USA (J. 1~. Alfaro and J. Keller)

Agricultural Engineering Department, Technion, Haifa, Israel (D. Karmeli) Agricultural Extension Service, San Diego County, Bldg. 4, 5555 Overland Avenue. San

Diego, California 92123, USA (C: D. Gustafson) Agricultural Extension Service, University of California at Riverside, Rrverside.

California 92502, USA (A. W. Marsh) Department of Soil, Water. and Engineering, University of Arizona, Tucson. .Arizona

85721, USA (D. D. Fangmeyer) Polytechnisches Institut, 75 Karlsruhe 1, Postfach 6168, Germany (Dr.-Ing. W. Stander) Soil and Water Laboratory, Irrigation Department, Yotvata, Arava Desert, Israel

(M. Shmueli) . - Soils and Agricultural Engineering Department, U.S. Department of Agriculture,

Agricultural Research Service, University of California, Riverside, California 92502, USA (S. Davis)

Water Resources and Development Servl’ce, Land and Water Development Division, FAO, r Via delle Terme di Caracalla, 00100, Rome, Italy

’ )h li

lrrigatio

Besides trickle irrigation (chapter 10)‘; interesting innovations include - special methods of sprinkle irrigation and subsurface irrigation. Examples’ . are-illustrated in FIGURES 61-68.

_- Y

FIGURE 61 Gated pipe delivering water in metered quantities from farm turnout or tube well to a series of furrows (or a border). Pipe is available in plastic (lay-flat or rigid), aluminum, or other lightweight, portable materials. Pipelines take the place of field ’ ditches and can convey water across uneven terrain, reducing the need for land leveling. They also eliminate ditch losses, which results in considerable savings in water. (U.S. National Water Commission)

t

105 I / -.

‘f c Y+ -.

MORE WATER i:OR #It111 LANDS L

FIGURE >62 Fixed-orifice sprayer irrigation in an orchard. Similar to tnckle irrigation in concept and design, it requires less filterin g. Evaporation losses are higher; winds cause the spray to drift, leaving dry areas. The larger areas of wetted soil may increase weed problems, and foliar damage may result where lo\\-cjualitv (c,~.. sahnc) watc‘r i\ used. (J. Keller)

/: .

OTIIER IRRIC;ATION METI-IODS 107 ,

FIGURII; b3 Spitters ‘and bubblers arc used to irrigate citrus 111 parts of the southwestern United States. The bubbler shown here delivers water to ;L basin dcslned to retain the water close to the trees. Water that KqGrcs‘littlc or no filtr:~ti~~n IS pumped through untlcrgrounrl plnstic p~pelincx to rcducc \ratcr-cun\‘cy~lncc lusscs and IS dls. chargctl as :I sriiall spray near lhc ircc. The basin mcthutl allo\~~s iIrlg;ltlon on slr)pcs and uncvcn terrain. (USDA Soil Conservation Scrvicc)

l~lC;lIRl~ 04 C‘enlcr-pivot sprinkkr irrig;\lioii spstcin nt Ktitra. Llb>,:l. klt‘cp in the Sahara Ikscrt. \\‘atc’r minctl t’rom ;I subtcrr;lnc;ln aclulf‘cr 1hr~~u~l1 :I ~~11,. at the pivot porilt Il:r\ producc~d 46;rop> 01‘ \\,II~~‘.I[ ;i11(1 b;irl~~!, ,~iid I I! (,I‘ .Ill‘;klt’.l pc*r >‘car 1‘rom land that ncvcr bcforc supper cd plant lift. The ccntcr’pivot IS the simplest full!, .lutomatic, irrigation system. A rigi d pipe up to 500 m long is suspended .lbove the crop <In wheeled caniagcs. The pipe is rotated around the pivot point by h!,dr;lullc t)r clcctnc motors at each carriage. Capable of providin, _ 11 hi&-qualitv irrigation iiith a minimum of operator espcricncc. this irrigation system is best adapted to high-intalkrate soils requiring fre- qucnt irrigation. (I). Buycs) e

g

2,. -& c

iOS- . . _

-LORE WATER I-OR ARID LANDS

FIGURE 65 Perforated pipe operating at about 1 atmosphere pressure is a suitable irrigation system for soils that take in water rapidly. The aluminum or plastic pipes are easily mova.bfc and can b? supplied from low-pressure mainlines. The plastic pipe in this esamplc is collapsible (lay-llat) and can bc cssily rolled up. Gravity pressure is often sufficient, so pumps are unncccssary. Little or no land shaping is needed, and, as shown in this picture, the method can bc used on sloping terrain. A relatively clean ivater supply or system is rcquircd. (Rho@;1 Journal of Agriculture)

.

.

I~l~;URll 66 Wet spots from subsurface irrigation. This mainly experimental technique cmplo~~s lhc concepts’of trickle irrigation, but the pipes are buried “in the soil, and the .. water is relcpscd at the crop root level. The water supply is controlled so that as little ---f water as possible reaches the soil surface. On the dry surface evaporation is feduced, which saves water, decreases salinization of the soil, and also allows the use of more saline 1 water (the salt-concentrating effect of evaporation is reduced.) Like trickle irrigation, this system is subject to orifice blockage, but because the water is released Qelow the p ground it may not be noticed until it is too late to save the plant. (S. Davis).

I.

OTl-1ER 1RRlGATlON ME-l-I-1ODS

i

FIGURE 67 Subirrigation in the S&r Luis Valley, Colorada, USA. As in FIGURE 66; this method irrigates the root zone without wetting the-soil surface, but it also arti-

Zflcially raises the whole water table into the root zone. In practice, the water table is supplied from border ditches. Small barriers are used to raise the water capillary action raises the water table throughout the field. Because comes up from below the root zone, very little reaches the soil sur evaporation, salinization, and weed germination. (USDA Soil Conserv

110 ‘MORE WATER FOR ARID LANDS’ n

.C FIGURE 68 Pitcher irrigation, a new development, uses unglazed baked earthem pitchers, which are widely available and very cheap in many developing countries. The pitcher is buried to its neck in the soil and filled with clean water. Vegetable ‘seeds are planted around it. Enough water soaks through the porous pitcher into the root zone to maintain plant growth. Experiments in India have grown melons and pumpkins to maturity with very little water (less than 2 cm/ha for the entire 88day grow$g period). Very little evaporation occurred because there was no standing or surface wate,r. (Picture ” and information supplied by R. Cs Mondal, Central Soil Salinity Research Institute Kar&l, Punjab, India)

12 Reducing t Cropland Percolation L&s I

. Of the many kinds of agricultural /soils, sand’*is one of the most challenging. tiillions of tillable hectares of sandy soils, widely distributed throughout arid regions, are se:ldom used ,for,agriculture because of their low productivity. Frequently, this low prodnctivity is due to an inability to prevent water from percolating away too rapidlyafor plant growth. Growing crops in sandy soils thus requires frequent irrigation; in many arid regions this is not practicaltparticularly if rainfall provides the only water,

- Techniques have been developed to produce artificial underground s moisture barriers that-keep water and nutrients from percolating below the root zone. A properly engineered artificial moisture barrier can overcome many of the hydrological disadvantages of sandy soils. By retaining more \ water in the root zone, it can create a soil suited to crop production (see

: FIGURE 69). 3

I.. _ Moisture barriers occur naturally in some deserts where, for example, sand a,~. overlies a less pervious loess soil and ‘are often revealed by luxuriant growths

e D

I

I .

9

e

of wild vegetatisn. 1.

, I -

Method

Undkrground moisture barriers are con’tinuaus films of a water-resistant - ‘-material placed approximately 60 cm belo&. the soil* surface with gaps every

150 m or so for drainage. . i Although. most barriers have been made of asphalt, ‘%ny durable water-

impervious material can, in theory, be used. Plastic sheets have been used for this purpose in East Africa4 *;

d layers of compost or manure rich in colloids

have been used in Hungary.4 ‘” .

40Gerakis and Tsangarakis. 1970. (See Selected Readings.) 41 Egerszegi. 1964. (See Selected Readings.) d

-u d 111,. :- - )’

--I -

, 7.


FIG’JRE 69 Retention of water above an asphalt barrier 24 ‘inches (60 cm) deep in fine sand. (A. E. Erickson)

The pptimuzl depth for the barrier depends on the moisture-holding characteristics of the sand. The extent of the barrier is determined by drainage considerations.

r Y r

One way to install a barrier is to rerriove the topsoil. hand-place the moisture barrier, and then refill the area. But machines have been built that will install a waterproof asphalt barrier without excavation. A wide, wedge-shaped plcjw pulled through the ground (50-70 cm below the surface) lifts the s ‘il and nozzles spray asphalt into the cavity. The asphalt immediately har i ens into a moisture-proof layer 2-j mm thick before the

” 42 earth falls back in place.

Advantages

Unlike many other soils; sand has a surface durable enough to withstand the abuses of tillage an,d ‘farming; it allows quick intake of rainfall or

42Erickson. 1972. (See‘Selected Readings.) *

’ Fe

REDUCING PERCOLATION i 1’3

FIGURE 70 Spring-planted, furrow-irrigated sugaicane growing on a fine-sand soil in Taiwan. Cane to the right of the stake is gowing over ,a moisture barrier. After 1 year the carie on the barrier yielded 104 MT/ha compared to 54.2 on the cont.roI. The barriered soil ;cquircd only 90 mm of irrigation, while the control nccdcd 28 1 mm. (A. . IX.. Erickson) ,&de’ _I

;:- .Fc

irrigation water; its good capacity for aeration fwors root dcv~loprnent; and its upper layers often serve as a mulch, reducing losses from evaporation

(chapter 9). When its low capacity for retaking’ water is corrected. sand can become highly productive.

A barrier give,s sandy soil a storage capacity ‘cquivalcnt to that of a better agricultural soil in a tempcratc region. Thus, barriercd soils require less frequent irrigation than unbarricrcd soils ‘and can save SO-75 pcrccnt ot irrigation water.4 2 Barriers also allow furrow or border irrigation on sandy soils that otherwise could not bc efficiently irrigated by these methods. In ;I tidal area in Taiwan, an experiment has demonstrated the use of barriers for restricting the upward movement of salt into the root zone. 43

Sandy soils with barriers can produce crop yields equivalent to those of the best soils in their areas and much higher than those obtainable from the original sand soil. (See FIGURE 70.) Yield differences between barriered and

42Erickson. 1972. (See Selected Readings.) 43Wang, et. al. 1969. (See Selected Readings.)

114 hiORE \VATl:R FOR ARID LANDS

nonbarricrcd soils generally depelld on the amount ,of drought during a particular season.

Field studies have shown that barriers prevent fertilizer. as well as water. from sinklng below the root zone.

In many ways subsurface moisture barriers bring advantages similar to those of trickle irrigation (chapter 10) to sand soils. The preferred method for

.- a given site will dcpcnd on such matters as the crops to be grown. the qualit) ol‘ tl~c wntcr, cconomicq, and the operators’ prcf‘crcncc.

Limitations

Today, the cost of underground moisture barriers is high.- lxgcly due to the cost of the barrier material. To install ;I barrier in the linitcd States using the mechanized system costs S625-$750/ha; thus. It ~a11 bc used onI) where agricultural production on marginal .land is desperately nccdcd. where the soil is otherwise useless, where high-value crops can bc grown. or whcrc

‘I tialcr is in short supply. Deep roots pcnclratc moisture bai-ricrs but do not cvntinuc growing in the

0 water-dcI‘icicnt soil below them. Crops with deep roots, cspccially tap roots, could, tlowcvcr, cvcntually pcrt‘oratc the barriers and rcducc their cf‘ficicncy.

The biggest technical problem in ‘producing ;t molsturc barrier is to SC:II the joints bctwcc~l succcssivo strips. This’ is particul-arly so in barriers laid bj mcctianizcd systcl]is.

The ctucstion o’f whcthcr salinity builds up in the ‘2 i soil bccausc’ drainage is

retarded by an ~mdcrgrouiid’~l,oist~~rc barrier is not complctcly answcrablc today. Since no barrier yet .$uiJt has bcsn completely ivatcrt+ight, drainagr has leached the salts away (chapter 3) and kept them within acceptxile levels. In some cases, howevgr, a certain amou!lt of irrigation water must be reserved solely for Icaching.


Underground moisture barriers have beer1 dcvelopod to the point at which researchers believe they arc ready for comrncrcial :\pplicutiun. Field cspcri- incnts have been conducted with vcgctabtcs and ticId crops, with and without irrigafion, in Egypt, South Africa, and Swaziland; in wet and dry regions 01 the United States; and with rice and sugarcane in Taiwan.

Under prcscnt conditions underground moisture barriers are economically feasible in ~mny areas of the world, but only for high-profit crops. With man’s increasing need for additional land and water. this technique may prove increasingly valuable as a way to produce more food on otherwise unproductive sandy soils.

Needed Research and Development

Further cff‘ort is needed to reduc’e’ costs, perhaps through development of neti, cheaper materials.

No serious danger’ of salinity buildup is anticipated with guod water .e management, but I‘urthcr research is needed to settlc this point.

Selected Readings

I;ricksr,rJ, A. 1.1.; (:. hl. Ilanscn; ;1nt1 A. 1. hl. Smuckcr. 1968. The ~nllucn~~ ot‘ subrurfauc 1 nsphalt Ixirricrs 011 the witcr pr,rlpcrtics and the productivlt\. of sand soils. In Tratrsocliotrs oj 11k~ Nirrlir It~t~~rtrutiotral (‘otlqp*.ss of Soil Scic*tlw, .Aticloitlt~, .-ltrstrulra I :33 l-7. (C’trpics 3vail:iblc I‘rurn A. E. ISricksun; xc Cont;icts.)

(‘;cr:Iki.s. I’. ‘A.. and (‘, %. Tsangnrakis. 1970. Undcrgrouncl mulches m central Sud;ln. f:‘osr .~~ljricmtr ~l.yrrcw/trrt’c* orrd i:orcpstr,l ./orJrtru/ 35.254-6.

Iho, k. V. I’., cl al. 1972. I mpcrvious I:lysr , ;I tcchniquc to incrc’;isc 1rr1g;it1on cfticicncy. ltrtlirttt /~tirtrtitr,r: 22(4):36-37.

Sl\srlla. c;. K.; L. C’. Ilam~nontl; and II. W. Lundy. 1967. licspun~c of wxral vc~ctablc crops I;) undcrgruund ;13l~l1;1lt inolsturc‘ barrier in L:ikcland tim wnd. /~‘lorrrla Sluff tlorric~rllrrrrrl Socieiv Proccwlir~~~~ HO: 2 1 1 -I 7.

Sumner, M. I:. I97 1. Asphalt, the IICU’ trcatmcnt fur wndy bowls. Fbrttrrttg So~rrlt .-ljiico 46( 10): 35-39.

Wang, C. C.;‘K. Y. Li; C. C. Yang; and F. W. Ho. 1969. The Ejji’ct of:-lsphalr Barriers on the hloktwe arld Sqarcatlc Fields oj Saud Soils. Taiwan Sugar Experiment Station Rcscarch Report No. 5. (Address: Tainan, Taiwan.)

Contacts

AMOC’0, Moistnrc Barrier Cu.. 200 LISI R;lndolph Drive. (‘hicago. Illinois 60601, USA. “(W. 0. I:r;izicr)

Arizon;\ Agricultur;\l 13slxrimcnt Statibn, \‘uwl, Arizorm 55364. USA. (I~. C;:~rdn~r) Crop ;rrltl Soil Scicncc l)tlpartmcnt, hiichigan State Univcrsi!y, IGist L:~nsing, Michlg;ln

48824, USA. (A. 17. Erickson) .

I1cp:lrtmcnt 01’ Agricultural Engineering, Indian Institute of Tc~l~iic~lo~~~. liharlragpur,~ W’cst Bqigd, India.

Ikp;irtiiicni 01‘ Agronomy, Univcr%i[!; of I-loridu, Gaincsvlllc. Flon>a 3 260 1, USA. (1.. c‘. IHaninioncl) .

l)ep:lrtn;~cnt of Soil Scicncc. Univcrsit!, of Natal. Pietermaritzburg. South Africq. (Xl. I<. Sumnicr)

Research Institute of Soil Science and &ricultural Chemistry of the Hungarian Academy of Science, Budapest, IHungary. (S. Egerszegi)

Taiwan Suggr lispcrirnen,t Station, Tainan, Taiwan. (C. C. Wang) -

,: I, ,-

\ ’ -

. .

rantipiration

‘!

Only I pcrccnt 01‘ the water al3st,rlxd hy rools 15 er~i~~rporalcd into tlic

plant cells; 99 pcrccrit moves iip Llirougti rllc pl2111 a~itl pdsscs ilit tlic’ at-

mospllcre as waler vapor. This process. caltcd rra~lspirutiorl. dil‘lcrs l‘rom

evaporalir)n in that it takcs~placc 011 living tissue 2nd is iniluoriwd by the

physiology of the plant. One ha of growing vegetation can transpire xi

much as 94,000 1 of water per day. If a practical way to reduce transpiration could be found, substantial reductions in water demand could be achieved, especially in arid Jands:

Meth6cls

Transpiration losses can be reduced in the following ways:

d

. Destr-eying unwanted phrcatophytes- plants that transpire efficiently. 3 Phrcatc~phy tcs, such as salt cedar and mesquite. often have roots that penetrate groundwaters at great depth. The groundwater losses they cause are not widely recognized, but in the semiarid western United States it has been estimated that phreatopliytes covering 6 million ha cause a total loss of over 25 billion. m3 of water each ycar.44 ,

. Hrcccling plant varieties that transpire less (chapter 14). 1 . ” l Enclosing crops within a structure (chapter IS> so that transpired

‘I water can bc’collcctcd and rcuscd or so that the humidity rises and retards the transpiration pfoccss. I

. Reducing air movement over a crop. by, for ~‘-1;ample. windbreaks of k interplanted rows of taller plants. p

. - Removing unproductive lcaves physically or with defoliants. In crops

such as wheat and barley, upper leaves contribute most to the developing grain. Removing the l&w leaves. if properly timed, can reduce water lost by ’ transpiration with Little or no loss in grain yield,

f Using chemical antitranspirants. “.

44’Robinson. 195 2. (See Selected Readings.) ,, 1 .

I 116 P

, . R~DUOIN(;TRANSPIIiATION 117

Transpired water is passed out of the plant through stomata-pores in the leaf surface through which carbon&oxide, oxygen, and water pass. Chemical antitrartspirants are sprayed onto the stomata-bearing surfaces of the le-aves (usually2 stomata are concentrated on the undersurfaces) to inhibit water passage. Although the technology is embryonic, present antitranspirants hnvc’ reduced water losses by 40 percent in some experiments (FIGURE 71). The frcqucncy of spraying depends on the antitranspirant’s durability and the rate at which new foliage is produced. Present evidence indicates that most untitranspirants may be effective l-4 weeks, although some reductions in Iranspiration have -been observed over several months.

Chemical an titransp’irants work by Y _I

0 Closing stomata;

0 Forming a film over the stomata;.or

m Cooling the .leaf with a reflecting coat that reduces the amount of solar energy absorbed. ”

Stomata-closing Materials

The openiqand closing of stomata are caused b\r two Iri$ly specialized gua1.d cells surrounding the aperture. Several chemicals can preven t.complcte opening of the guard cells, thereby decreasing the loss of water vapor from the leaf. Most promising of these inhibitors are certain alkcnylsuccinic acids and abscisic acid.

Film-forming M,aterials

Lcavcs can bc covered with films that form transparent barriers to the escape of water vapor, Materials tried as antitranspirants include cetyl alcohol, silicones, wax, kites, and plastics. These film-forming materials re- duct transpiration, but the yet unrealized ideal is one that is: . e ‘Nontoxic to plants and animals; ’

l MO,! ii

permeable to carbon dioxide and oxygen than to water vapor, so that the pla t’s metabolism is not slowed;

. mldY P ermeable t’a, the wavelenghts of light that most promote photosynthbsis; rT ‘- c

. Flexibl e enough to &ow for leaf motiop and expansion; l ResiStant to degra’dation by sunl,ight,! microorganisms. and physical

disruptions! and D l ‘Ecot.\omically attractive.

I m


, f unsprayed FIGURE 71 Matched sugarbeet plants, one treated with an antitranspirant. were irrigated to saturation and then allowed to grow without further water. Three days later the trcnted plant still rctnins its moisture and turgor; the ?t!~er has \!4ted. (R. Xl. Hagan

Reflecting Materials

Rcllccting materials sprayed on Icavcs rc‘ducc> tilt s~jlar cncrgy absorbed , and lower leaf temperature and tticreforc slow do\x,n transpir;l[lon. Rctl~ctlng matcrirk do not normally nuxl .tu block stomataI’ pores on the undcrsurl;lcc of Icavcs; they intcrrcrc less with oxygen and curbon diosidc transfer than do the other chemical a.ntitranspiiGnts.

Advantages _,

Reducing transpiration reduces a crop’s ‘demand for water th”ereby ’ allowing some crops to be grown in arid areas whqre the water, supply is

c ‘.

other wise ‘irlasbcqutitc. Lvcrl ;I small rcductlclrt Irl tr;Ir1spll-;ltlclrl rcsulrs In ;I . major water saving, bccausc nul-rnally most ul‘ the ~yatcr absol-bed 1~1; ;I crop IS

transpired andibcc:tus~ w~tlun tfic plant itscll‘ IS [tic‘ most ct‘l‘iilc~nt $;~cc to s’avc water. Ariy saving at the plant is cqulv;llcn[ 10 ;I rn;~n~*f’~)ld sa1~111~ :~t

&rlicr points lkcausc 01‘ Iosscs in storage. ~oI.lVC\~;Irl~c’, Lllslrlj>u[I~)ll. ;illL1 I iclL] app!icatioli in the irrigation s\‘stem. -

A modest reduction in transpiration has been shown to Improve yields and quality of; some flower and fruit crops because I&s moisture and juice are lost from the ll~~wcrs and I‘ruit.(FIGIJRE 72).

Limitations 1.

The lilnitations ol reducing trarlspir;ltion wutcr I,,sscs clthc‘r by brec,ding plants that. transpire less or by enclosing plxlts within ;i-stl-uc:turc ;lrc‘ coverc’d in chapters 14 and IS. Destroying phrcatophytcs IZ vc’q controvcrslal. it may

disrupt the always-t‘ragilc arid environment. Stomata serve as portals for the intake of‘ carbon diosldc (neccssaTy for

phcitosynthesis and growth): thus. a cheniical barrier against water loss ma) reduce plant growth it‘ it also interferes with the passage of carbon dioside. Today’s chemical- and i?lm-forming antitranspirnnts do restrict carbon dioxide movement an,d, thus, arc mo,ut useful wheie water conservation is so

.

important that masimum plant growth can be sacriliccd, as in the c3scs of. wild phrcatophytcs or plants for landscaping, lawns. and highway borders. ‘;;.

Some, antitranspirants damage plant cells. Many stomata-closing materi&: even when irery dilute, are to>;ic to some plant species and should be &d with care. Their effects on gnirt@I life have not yet been fpll~, investigated.

One effect of normal transpiration .is to cool the plant, and the Y’ I,

film-t‘ormirl’g and stomata-closing types of chemica‘ls can ndvcrscly aft’cct plant growth bccausc they tend to incrcasc leaf‘ tcmpcraturc slightly. I

I’rcscilt antitransfiirants al’fcct only 1hc Icaf Yurf‘acc 1~1 which they arc \’ applied and thcrcf’orc arc of little use OH rapidly growing crops whose ltai‘ surl’accs arc expanding rapidly.


Transpiration reductioq is mainly experimental today. ,Although great ““: potentizl exists, basic rese+rch or! antitransplr;lnts has sc) f‘Jr bscen meagqr and IIOL overly cncouragini for%‘theIr widespread 1~. But antltransplr~~nts can bc

used whcrc retarded plant growth 1s acceptable. b?.,

I&ring the early IYOOs, nurscrymcn and l‘orcstcrs dlppcd seedlings in W;LY . q)r was-oil crnulsions @ prcvcnt &ltlng, and thc&y lncrcascd the survival

rate ul‘ \hcir transplants. h4orc rcccntly in the United S‘tatc’s arltltrarlspir:t;1ts h;y& . .

‘_ ; .* Isl”rim~iitltlly spr;iycd.on a torcst to ~ncfc;lsc the \r’atcrsticd ruric?l‘l’.

. Applied t(l’ phrctiophytes t<) ‘curt:tit watt‘r 10~5 1‘r~~nl gr<.,undwatcI supplies; L Y , r /

. Sprayed, on highway* plantings wherz ir.rlgation IS cspensive and hazardous; ,

/ * - e.

. .. Used successfully ;o in‘crease .$e size and yield of orchard fruits b; -..-- spraying trees just: bef9.F: .harvest, when the stie depends more on Idqisturc

crmtcnt than on vcgctativi’ growth; and . Used to rcd& winter dcsiccat1qi 13 plants. cspcclally where sr)ilS are ” \

frozcri. I i . . . ‘A , . ‘I. Rcllcctan t materials 1 have been tried ,011 artithukk in Israel with

considcrablc SUCWSS: tlw pcrccntagc of cuttH& tha\ *rooted lnc’rcascd grcatlv. vugctativc growth was improved; and higher yields wcrc’ obtained.

d.. ’ * 2 I

Needed Research and Ejeve)opment ‘,’ I-

_/ Research and development -should be directed to Gie following: * Development of antitranspirants &at wilt gke a maximum reductionFin :;c

transpiration and jl minimLtn reduction in pholosynthesis. Recent ‘research

_ ~JtExMJciG~-iRANsnRATIdN 121 _-- tl &xi

h& donr,‘kch to help elucidite the mechanism of natural stomata control,: hut the interactimk of all factors affecting stomatal movement require * L j I I .

rmination of optimum concentrations and awlkation methods. vestigation of the numerous potent&l us& for ‘such materials.

* .T &se&h is also needed-to improve the delivery of antitranspirarits to leaf &tam, especially un’dersurfact%, that are difficult to cover. Ground a aerial spraying techniques developed for ,pezticideh may be useful, a perhaps the use of electrostatically-charged-droplet spraying could impr under-leaf coverage (the electrostatic repulsion between droplets spreads ,them

L over tie leaf surfaces). - ? -” . Research in transpiration reduction by using reflectants‘could be profi;

abl2, *,, c . goal $ to develop a systemic transpiration sup+essant, by the p&t and moved intt~&& to the stomata. This

d ensure Yuriiform leaf. coverage and you!d protect+ven new leafygowth. s,has n6t beeri achieved to date, although abscisic acid (a stomata-closing .

the,vase water of cut flowers has been shovkr to reduce water loss fioji the leaves.

_ e Chemicrd research is needed- to synthesize analog& of.“abscisic acid’and other inexpensive compounds that would permit widesplre;ad utilization of the

- s ’ * a 1. d stomata-clos&g method. 1

Reseaich & *‘us spirants to reduce moistunz stress during water-sensitive grow* s transplanting or germination) would help to,increase plant sunriv -*

@ou-Khaled, A.; R.’ M. Hagan; tid ,D. C 13avenport. 1970. Effects of kaolinite as a‘ .j reflective ~antitra.n@rant on leaf temperature, ~transpiratibn, phdtosYnthesis, and

water-use sfficimcy. IWer Resource I Rwurd’6:280$9. Btook, I$ Ne +nd D. B. Thoruh. 1971. A;qti~~ksPtit effects dn the tnbpiration and

physiology bf Tamariik. ~ter’Remu.rcca RewPr&‘77:499-5 lo., I Dawmport, D. C; R. bl Hagan; aiid P: E. Marti& 1969: Antit~anrplrants research ani its

possible application in hydrology. Wrtet Resmmes Research 5:73543. J+venport, b. C.; C. Uriu; P. E. Marti& -‘iid R. M. Hagan. 1972. Antitranspikn~

increase~site, reduca mhrivel of olive fruits. CWifgnrh Agrkulfu~ 27(7):6-8. * JIavenpwt, b. C.;

growth. Jowno F . -Uriu;~~an~ R., M. F&an. 1973. EX@xts of film antitranspkants on

of Gxperimep~al Botany. (In press) * Gale, J., and R. W Hqgan. 1966. Plgnt an$ranspirantg. mAnmd &~FW of Hunt

R$ysiolqy ‘17 i ?69-$2. ’ . Gale, J., and A. Powoff-May&x, 1967. Pbstic films or; plants as antitranspirants.

Science 156:65?L52. JO-S, R., and T. A. Manafield. 1970. Suppression of stomatal operkgs in leaves treated

with abscisic acid. Jbumd of Expirimental Botany 2 1: 7 14. kkinson, K. J. 1970. The effects of sikone c$.ings on leaves. JQW-~ of Experimen@l

Bofany 2J 566. I i ,

A’ 3

122 i LORE WATER FOR ARID LANDS

Robinsop, T. W, 1952. ‘Phmatophytea and their ion to water. i weskn United Statea 7hznmct&ns, Adam Geofi-

*@Iitch, L-1969; Stomatal control. Am&u1 Revl I Plrryridogy 20:32940. - A

&j&& ---. , PC % ”

Agricultural Reseagh an~Edwation Centei; University 0; Florkin. Pb. Ebx’1088, L&e Alfred, Florida 33850, USA CL. G. AMgo,

Agricultural RestsarCh Institute, Raya&, b&non (A. Abou-K ,d). .- Agriculture1 Research Orpniutictn, The Vdlcrni Center, P.O.B. 6 Bet Dawn. kzwz~

(C. Stanhill) Department of Bo’tan~,dl&rew ~kztsity, Jcm Department of (%embl Engineering‘U&enit r, C&ado SbO2,

USA (F. Kqith and A. TaotiA Dbpartmetit of Fore&y, University of Wisconsin, Mndisctn, Wisxmnpin 53706, USA

(T. T. Kozlowski) Department of Water !kience and En-ring. Univeni f califorrlin at via. Davis,

California 9q616, USA-@: M. Hagan md D. C. @~nport)‘, Department of Waterxhea Management, Univtity of Arizona, Tucson, Arizona 138721,

USA ID. B, Thorud) _ , . .-.

. e

14 c Seled@g and IUkagiAg CmpS - “- ‘To.- Us&’ Water More- Ef f iCierMy 1

/ .*

’ Mos’t crops grown under irrigation in arid region3 were imported from ‘more temperate regicrns where efficient water use ‘is not required. Some may need over 2,000 kg of water to pro&e 1 kg of usable dry matter. Since

q -little has been done on the selection and breeding of food, fora&’ and industrial crops ~scifically to use le; water per uNt of product, much re-

’ &arch is needed in this area. At the same time, wise.seleciion ofcultural practices tin do mutt t’o improve the efficiency of water t~se.~’ .

-3 * ( 7. D

MdXBdS . _’

Selecting P&t&x WatwUti Efficiencj - e

*A, breeding’ program ked at developing c&ivars~‘(varjeties) for agricul-‘ tural use under arid conditions can be approached (13 by s&cting wild plants tiyt now survive’:m* desert conditions and putting them to use as food or cash crops; or (2) by selecting Individual waterefficient $ants from varieties of

‘, alkad$diimesti~ted crops &ch as barley; sunflower, melons,,s&ghum, pearl ’ “millet, tid beans,. and using t&m ~JI breeding programs. Many of our present st@e crops- iappear to have. originated tmder arId or ,-I conditions.

- vkhich sugg&ts that: ap&priate genotypks should be available.- Ahhough ’ .’ native desert plants. shodd not: be ignored, the besi’ &ndi++s for .M@~ly ‘.

useful plants Mth Iow,s~ater re@$emeiits seem to be ai~dydor@icated ., ones* - I’ _ ’ B -

L, -&lection can:‘@e h be &sed &%su.a) obseiaxon oi varjeties &iving

WWith $J marginal Water supply; but there use&as guides for +el&ting ymising v

several charq&eristics tha’t Can .be The ~follotig kinds of plants

seem- to offer,prornise;’ -k-~, Plants that grow in cool seasons when &poration rates are lower (e.g;,

let&ce~. ~ i . ;-

I/ . : -Q -’ * 45~~ ‘other chapter?k this &port arc ielcvant to

some sp!?Jcitk subjects not &ah with Clsc~.” this’topic. This ch&er deals with * . l *

. . .

+Ku *

124 MORE WATER FOR ARID LANDS -

l Rapid-growing plants’(birt without greatly increased water require- . ” ments) that .shorten the time. in which water is lost by transpiration and ei;aporation.

‘e High-yielding plants that require no appreciable increase in.. water , supply,for example, the short-strawed wheat varieties evolved in Mexico that give double7 or triple the yield of older wheat varieties without increasing water demand and can double or triple water-use efficiency. .

l Plants with low transpiration losses (chapter 13). For example, agave and pineapple close their xtoma~a during the ‘day when evapotranspir losses are greatest; they ,consume less water than do plants that open stomata during the day. Selection or breeding of plantb’ to increase da stomata closure could. reduce water loss. An alternative is to select,species with stomata placed, distributed, or structured- to transpire less water. For! example, plants with most &’ their stomata on the undersurfaces of the lea&C gentklly transpire less than plants -having stomates on Beth sides. Arrange-

size, and shape of individual leaves may also-p&e important. P-tits tall, op&n leaf structure, ideally suited to absorbing the Sun’s heat,

.,

,

transpire water faster than plants with a lower, more compac~kaf structure. l

d

. Plants that can tolerate lowquality (e.g., saline) water (chapter 3). ’ Drought is unquestionably the. most impckant environmental factor

influencing the growth’of plants in the arid regions of‘th’e world:.The small ’ amount of rain in arid lands is intermittent andSwnpredictabk; any~atid-land crop has to survive droughts. Various characteristics, such as deep,‘well- branch_ed roots, can be used 3 selection guides for pknts that are drought resistant, but the basic physidlogy of the drought-resistance process in plan’ts _ ’ is complex and little studi-ed c

I

Ma*iging Rants for, Watt+lJse ,Efficbcy

b In arid lands water supply is *often pot the major factor in crop y&&d;

sometimes the crop’s, environment is the leading cause of ineffidencics in water use. ‘For example, insufficient, fertiiizcr, insect control,. or d&ax contra!; impropk cukivation; and excess weeds all reduce the yl’eld and thus reduce water-use efficiency. Crop management that increases production also ,mcreases water-use efficiency. ’

.

Cultivation practicks must-reflect the importance of helping the plant’s root system to-‘extract meager moisture from arid soils. Practices that increase the rooting volume of the soil kill improve yields and water-use efficiency. On the other hand, practices that jnterfere titb roots may have adverse effects in arid lands, even if they are successful in temperate climates.

I *

WATERkFFICiENT &OPS .

125

Plant populations must.be large eno’ugh to permit fuh use of the available moisture, yet not so large as to reduce yield. Because variable rainfaLl makes it dii_fficul,t to prejudge the moisture that wilJ be available.during the @wing

’ Gason, the ta& of selecting optimum population size is difficult. Cultuihl L c practices that result -in overgrazing also reduce water-use efficiency by

mstriciing the dTth and ramification of the grass roots. Part of the reduction” in yield experienced on overgrazed ranges may be due to a lack of sufficient vegetation to hold the rain and snow that fall. Thus, pasture and *range management practices that minimize runoff and maximize infiltration use available precipitation more efficiently.

--

Qltivating crops in rows on the contour increases the infiltration If rainfall and reduces water and soil losses. Thorough weed control in fallowing operations facilitates water . storage .by eliminaJing transpiration losses (chapter 13). Leaving crop residues as a mulch often conserves water ‘by reducing runoff ‘and increasing infiltration. The mulching also reducesa evaporation .losses (chapter 9).

The date a crop is planted influences .water-use effi&ency. ,Gnerally, the ae earliestsafe plant&g date is b&t, because the plants can utiliie accumulated

. wiirter moisture and take. advantage of cooler weathe’r &d, thus, lower yapotranspirabon rates. \ w

i 1,

Improving the water-use efficiency of a’ crop saves water at a <most effective .point, i.e., at the end of the tiater supply and delivery system. A 20

L percent sav&gs here may be equ<valent to a manyfold @crease in the supply . at the watershed! Large areas of-water-defitient and marginal lands could be made productive .with appropriate plants, if coupled with management

. . methods adapted for the- area. Drought-resistant plants with high water-&e efficiency could play. a preeminent iole in the progress of’runoff agriculture (chapter 2). . .

i

Limitations

Genetic inylrovemento take uuch time; however, .-

selection of species, varieties, and ecoty@,es for most efficient water use may be important enough to justify active investigation. Cultivars and ecotypes must be selected not only for their water-use efficiency but also for their hardiness ,anh drought resistance. ’ 4

126 * / *_* MORE WATER FOR LANDS

Stqq of Development I 1

cists breemZlg plant v%ieties idapled ta arid regions have been inQRct.ly selecting plants tht use water efficiently. Bu”t little or=no research has been specifically directed to improving *water use or determining the fundamental parame’ters’ in plant phys$ogy that ‘promote,it. In relation to 1%

’ pportm the effort nowexpnded,is s@ll. - ’

‘.

PNeeded Research and Devalo~t *

There is a disperate Geed for selection of rop varieties (particularly for l high-protein range tid forage crops) that usiless water. Fundamental to t&s is the need. for simple, rapid tests and measures for, water-use efficiency in plants. . a

c breeding f0.r drought resistance has been carried on; thus ms*are neeQed to select usable xerophytic (drought-resistant)

’ plants, .In general, physical characteristics such as water requirements and transpiration rates andaanatomical and morphological chafacterisfica-do-not

de simple and practical indicators of drought_resistanca?‘.‘There is an urgent need for fundamental research in this e&y”:’

Basic research into photosynthetic efficiency lhd plant hormones is needed to determine if there is a biochemical method‘to-rapidly identify and quantify water-conserving and xerophytic characteristics.

Even today, there is little recognition ,of e need for plant vfrieties with lower water requ$ements. A survey of pro

~ 3 ing crops and a collection of

germplasm of varieties ivould make a valuable,contribution to the develop ment of arid-land agriculture. P

*

Seied RefLings

Arnon, I. 1972. OopJrwdu’c~bn in or>l Regions, Vol. 1: ‘Backgroud vd Rhciple~.

Barnes and;Nobl6, Nah’ork, and Leonard Hill Booki. London. 650 p. = Burton, G. W. 1964. ‘.I?I& geneticht’s role in imprbving water-use efficiemy by crops. III

Remch on titer: A SyFposium on Problems and probrrss. ASA Spahl Publication No. 4. %il Science Society of America, 677 Soutkscgc>e Jhad, Madison, Wisconsir\53711, USA..p. 95. : *. F ..,

Connpcticut Agricultm Ejtperiment Station. 1943. Sfornuric and htrr Rebrion~ J+I ’ Plonfs. Bulletin Number 664. (P.O. Bori 1106, New Haven, Connecticut 06504, USA)

Euenari, M.; I.+ Shanan; artd N. Tsdmpr. 1971. 7Ie h%?gcu: 7Rc Utdlenge of (I L&serf. .c , HarvardUniversity Press, ambridge, MaJ&husetts 02 138, USA. pp. 229-300.

Kramer, P. J. 1969. Hunt and Soil Water Relationsl$ps: A Modern Synthesis. M&raw Hi& New York.

‘National Water Commission. 1973. Chapter 7. (See p. 5.) Slatyer, R. 0. 1967. H&t- Water R&tionships. Academic PI&s, New York.

Y

’ I 5

.

* ..”

- WATER-EFFICIENT CR&S * 127

?

Ij (-’ ,h

I + So\ kience Society gf Alnerica, 1966. Piant Environment and Efficient Wufer Use.

i:. Special Publication.-fAddresK See I&ton above.) UNESCO, 1’960. P&t- Water d&tio ips in Arid and Semi& Conditions; Reviews of

‘,, -q 1 Research. A!rid Zoqe Reseqrch serie Vol. 15. Paris. 225 p.. ? . *

_ c l \

_. . . . contacts -_ . BlacklanG Conservation- Research Center, ;:S.‘. Department of Agriculture, Soil and

Water Conservation Research Division, Temple, Texas 76101, USA (J. Ritche ) Departmerit of Agronomy, Cornell rynivcrspy, Ithaca, New York 1485 , USA ff

a (E. R. L.cmon) / ‘apartment of Agronomy and Plant Genetics, Univdrsity of Arizona, Tucson, Arizona

85721, USA (M:. A. Massengalc, A. K. Dobrcnz) . . Department of Botany, He+w,University of Jerusalem, Jerusalem, Israel (MP Evenari) Deptimcnt of Water Science and Epgincering, University of California at Davis, Davis,

California 95616, USA (R. M. Hagan) Ev89stra.nsp~~~tipn.LaPdfatory, Kansas Stats&ivefsity, Manhattan, Kansas 66502, U&A . -‘. .,.

‘! (E. T:kancmasu) , . ” . . .-.. :. -

i-pgia Agricultural Ezperiment Station, @cultural Reseirch Service, U.S. ppart- ‘A.’ ment of Agriculture, Tifton, Georgia 31794, USA (G. W. Burton) -

H”----- . Intenrptional-Crop5 Research Institute for the Semi-arid Tropics, 1-11-256 Begumpet, Hyderabad 16, A.P., India’(R. Cumminp, Director) .’

Negev Institute for AridZoni*esearch, Beer S@va, I&e1 (hi. Forti) L U.S. Salinity Laboratory,‘Agricdltural Research !Zrvice; U.S. Dcpartment‘of Agricultyrt,

- Riverside, California 92502, USA (1. van Schilfgaard&) c . U.S. Waer Conservation Laboratory, Agricultural ReseGcli Service,W.S. Department of

Agriculture, Phoenix, Arizona 85040, USA (W. L. Erhlerj ^ Water Resources arid Developrtrent Service, Lan‘d and Water Development Division, FAO,

Via &lle Termc di Caracqlla, 00100, Rome, Italy n

-

. .I _

WATER-EFFICIENT CROPS ~ 127

. l 7

Soil Bcience Society gf America, 1965. Bunt Environment and kfficient Wuta Use. Special fiblicati?n.-fAddres See Burton above.)

p UNESCO, 1960. Plant- Wuter Rzlatio T

ips in Arid and Semiaid Conditions~ Revbvs of d Research. A!rid Zoqe Reseqrch serie Vol. 15. Paris. 225 p. . . _.

8 \

. . contam . . . Blackland Conservation- Research Cpnter, 6:s: Department of Agriculture, Soil and

Water Conservation Research Division, Temple, Texas 76401, USA (I. Ritche ) Departmerit of Agronomy, Cornell lynivcrspy, Ithaca, New York 1485 , USA i

* (E. R. Lemon) J ‘D&partment of Agronomy and Plant Genetics, Univdrsity of Arizona, Tucson, Arizona

85721, USA (M,. A. Massengale, A. K. Dobrcnz) . - Department of Botany, Hc+$w,University of Jerusalem, Jerusalem, Israel (M~Evenari)- Depdrtment of Water Science and Epgineering, University of California at Davis, Davis,

California 95616, USA (R..M. Hagan) EVapstra.nJpi;r~~~pn,Lapp’fa,tory, Kapsas Stato,&Gvefsity , Manhattan, Kansas 66502, USA . ’ (E. T.-Kanlmasu) , . ” . : . .~. : .,-

Lpgia Agricultural Experiment Station, @cultural Research Service, U.S. Qepart- ment of Agriculture, Tifton, Georgia 31794, USA (G. W. Burton) .

IntentptionaIcCropS Research Institute for the Semi-arid Tropics, 1-11-256 Begumpet, Hyderabsd 16, A.P., Inti’(R. Cummings, Director) .’

Negev Institute for AridZoni%esearch, Beer Sheva, Ishel (M. Forti) . U.S. Salinjty Laboratory~Agricfltural Research“$?.rvice; U.S. Dcpartment’of Agdcultyrt,

* Riverside, California 92502, USA (J. ti SchiIfgaard$) e _ U.S. Wqer Conservatiop Laboratory, Agricultural Res&cli ~ervicc,W.S. Department of

Agriculture, Phoenix, Arizona 85040, USA (W. L. Erhlerj - Water Resources arid Development Service, Lanzand Water Development Division, FAO,

Via delle Termc di Carnqlla, 00100, Rome, Italy ^

-15’” Controllhd - Environment 7 Agrjculthce I

. . b

.

By. encapsulating+ crops’ within s’peciaIly’ developed enclkrres, high a‘gricul-turak productivity .can be- achieved~with -lirnited~ amounts. of .water.r . Water normally lost by $&page, evaporatikr; rind transpiration (chapters 7, 8,

. 9, 13y is, retained. and reused within the enclosure. Thus, in vt terms very__ little water is needed to produce the’crop. Within the enclosureJ&h-t;;h~at, water, humidity,, c&bon dioxide, nutrknts, and pests are manipulated and

-. balanced to produce yields often ten times larger than those bf”conventional outdoor agriculture. Wjth special techniques most of the water low-quality water, such as seawater, otherwise unsuited to agric

c$n be *In

essence, .this method places crops in an environment that can be so c led that the upper l&its of their yield potential’are approqched. . .

‘?. _

*Methods

Enclosures may be transparent fiber~trktures, air-inflated bubbles; 0; low tunnels ovel the row of growing plants (FIGURES 73-X): ’

-Environknt flgricuiture .

ne system .‘pio,rkred by the University, 6f -Arizona’s Environinent’~ ratory and the University of Sonora, Mexico, can be used as ,an osed-epvironment agriculture. Plant+ are’ grown in inflated uses in which there is Iittle or no connecti0n.wit.h the outside

&de; the tir ‘is- continuously cycled’ through a stream of water 7.. - which humi~difies and cools5it. Brackish, silty, or sea water can be used; ‘the humidification $rocess leaves cork at a test facility % Puerto Penas&, Me

ts behind. Seawater: is used

irrigated with high~uahty water, bu+ on (FIGURE 74). The plants are mall-amount is needed because

. I 3 128 *

. , ’ Lcl

CONTROLLED ~~IR~MENTS - .

129 ? v’ - .

I * ; s FIGURE 73 Controllodenvironmvt complex in Abu DhHbi. Even in sucl$nho”spiTabk , terrain very .large quantities of agricultural pro&~ce can bpraduced @ICURE 76). (yi Land.s Reseaich Center, Abu Dhabi).

- t _, ,. * *

FIGURE 74 Controlled-enepnment complex k Pue& PenaSco, Mex&o: (vniveisity ,of Sonora) L .

~ .’

1.-j* *I * - MORE WATER FOR ARID LANDS ,

“the high kmi$ty suppresses transpiration and evapdration. Humidity is so high that in winter moisture condenses on the coql~walls of the greenhouse

. and is collected and reused. 1 I

For photosynthesis to occur, carbon dioxide (C’& ) mus~be added because in the closed environment the plan& quickly use ,up the availably C02. In Puerto Pefiasco scrubbed die&A-generatorexhaust gas, coritairiing large. amounts of COz, is introduced into ihe enclosure. Res’earch td date shqws tha\‘ this apparen.tly simple technique has promise, but problems remain, - es$cially in removing minqr contaminants that reduce crop productign.. In other close#environmen t facilities, bb t t CO2 and CO, generators burning natural gas (which &es a cleaner exhaust thin diesel fuel) are used to avoid the contamination.

.

FIGURE 75 Tunnelenclosure for stratiberries gkwn in Israel. ,(hiinistry. of Agri- dultke, Production and E~tensiori.Services, Israel) ,”

~JXGROLLED ENVIRONMENTS 131 ‘%. <> Partidly-Open-Environment A@culture

T I .

‘2 In partially-open-environment .agriculture fresh a@ is continuously Suppled IO the’interior of the en’closure and returned to the outside atmosphere. The air is passed through a stream of water whickan be of low quality. High-qua-

/ lity water is used for irrigating the crop, but because the high humi presses evaporation and transpiration, the amount‘needed is still far that for standard agriculture. Since~humidified air is continua

re, the total wafer requirement is more than that y ret for cl&d-en- .

iculture. .I

The University of Arizona has designed and provided consulting s&vices for three commercial installations using the partially-openenVironment technique. The first system installed (FIGURE 73) is in Mu Dhabi. In this facility the environment within the enclosures is humidified with seawater.

i ie ’ TcW% ‘i$ ‘generateed from -A ;-diesel ‘electric Engine, *and waste 5 heat from + the engine powers a seawater-desalting plant. Desalted’seawater’ irrigates’:! ha of controlledenvironment agriculture. The expensive desalted seawatef is used

” only to fulf&the relatively small requirement for irrigation water. m The second, and largest, commercial~facility is in Tucson, Arizona, whe

, ha of* partially-open-en~ronment gre$houses use underground water 4 both environmental cgmrol (humidification) and irriga&on. In Yuma.

Atizona, a 2-ha complex is being erected to ‘use brac&h groundwatcr for environmkntal control and to desalt sqme of it-for irrigation, using rever

. , osmosis. P This system has considerable prorksek aridareas where lowquality water

is a@ilable and high-quality water ii qarce. % .I

One -novel modification of controlledenvironment agrict&ire uses low plastic tunnels placed over the plants (FIGURE 75) to reduce evaporation . and traqspiration losses. T&s system @so allows environmental manipulation.

1 According to one report,46 c&bon dioxide added tu ‘the tu cucumber plants to develop more quickly; to fruit earlik, and t

* 45 percent more than in standard agriculture. Lettuce gave a- *-* increask, and sweet peppers set more fruit and gave a 20 percent increase in ., yield. In Israel in. 196667 over 1,200 ha were grown under such @astic covers. This m&hod made it possible to produce vegetabkvej early u-r the season when supplies from conventional agr-&ulture werc_meager-an&prices “._ .-- - s_~.l . e.._-.- high.

. d .’

46Moner. 1967. (See Selected Readings.) *

* ,

m + 0 I

* T

.‘132 a

hioRE WATER FOR ARID LANDS . ‘4

if .

c* 7 \

-. FIGURE 76. Quality tomkiocs grow-p;ofusely in a c~ntrdkdcnvironmept greenhouse at Abu Dhabi. (Arid Lands ‘Rmarch Center, Abu Dhabi) J . /I . .

Advantages

x obtained in contrblledcnvironment 70 t of to&toes and 6OQ-750 It of

cuctibers have. been ed,” and it is possible to bow three to eight 1ettuEe crops per year. To economic potential forithis

cucumbe,r, and -lettq& cro.ps offer the most tbday,.but 16 other vegetables and flowen

are commercial& produ@ nIrolledenvironmen#-agriculture fac$Jy in Abu Dhab?(FiGURE. 76); ’ . ’ I--_, 4

I c

CONTROLLED ENVIRONMENTS 133 .

Although considerable quantities&of water may be needed,. the system offer3 very significant water -savings in terms of the size of crop produced. If lower capital-costs could be achieved, whole villages, even in remote areas, could feed themselves with a.si.ngle controlledenvironment farm.

Limitations .” i

The major’limitation to cl+ed-environment agriculture is the high initial ‘capital inyestment. Based o University of Arizona experience: complete

’ facilities, including culturin quipment, packing facilities, etc., cost approxl3 ~ mately ,US$25O.OW- e$er;bing on the $egrce of sophistication. This crops can tz grown at present. Water is stih neede tio”ns kill be limited to coastal areas or other 1 where brackish or other water unsuitable for reular irrigation is .h

Of course, &k tunnel>nclosure system k much chkper, t it, too, siv& compared to costs of standard agriculture and only

pay;%ff ;when high-priced- produce is grown.

Stage 6f Dev;ilo pment )‘

The Aosedenvironmeat~ and partiahy-ope,n&rvir&rment pro&sscs are now . be. gmning to be commercialized. Because they are a very resent *elopment,

only a few fijcilities ark now in operation, but more are under consideration. 1 Plastic-tunnel a@culture is used to a limited ext ~ ,. * - * c _

“- hlended_Re+acch

Lower cost systems Gould* make .contr&ed-environm~t ‘agri$ture in- ‘. ? crt%singly attractive, and practical for’use with lower priced crops. Particu-

-.-_dady”iiR~~fi~~--- s regard is the need to develop lowco8t CO~~suppliw. ItA is also important to select varieties and develop crags that btter

tolerate high gret;rlhou’se temperatures and fhus permit higher yields, Other needs include: (. a%. - ‘I

Roofing that selectively transmits the wavele$ths of solar radiation /

l

that most promote plant growth; -’ .,

‘4, l ‘U&of hormonal or chemical sprays to protect plants against heat; and ’ . Studies of phytopathology and disease ..con;ol in the hot and

- extremely humid environment within the enclosures. #

134 MORE WATER FOR ARID LANDS 7 .

leeted Fhzylg? *

Dalrymple, D:‘G. 1973. ntrolled Environment Agn’cuiture: A Global Review of use Food on. U.S. Department of Agricultuz Economic Report 89. 150 p. availabk from Economic Research S’erviq, Room 3510,

South Building, U.S. Department of Agriculture, Washington, DC. 20250, USA.) En&h, H., et al. 1970. CO1 enrichment to cucumber; lettuce, and sweet pepper plants

grown’ in Idw plastic tunnels in a subtropical climate, Ismel JoumaI of A~culfwml Research 20(2):6 3-9.

Environmental Research Laboratory, University of Arizo a/Arid Lands Research Center, Abu Dhabi, United Arab Emirates. ,4nnual Re rf 19 71-72. (A&&k from pa Env’ onmcntal Research L&oratory; see Contacts.)

Fontes, M. R. 1973. ControUed environment horticulture in the Arabian Desert at A%u !i Dh&i. Hkfscience 8(1):13-16.

Jordan, 0. ‘W., and* T. ljuntcr. 1972..~ThC effects of l+ss clothe. andocslourcd polyethylene tunnels on microclimate growth, yiclb- and disease scvcrity of strawberry plants. Journal of Horticultuml Sci$nce 47:4 19-26.

Kloner, U.- 1967. Vegetable Growing-under P&tic Cover in Ismct <oduction and Extension Services, Ministry of Agriculture, Tel Aviv, Israel. 11 p. _

O’Leary, J. W., and G. N. Knecht. Increased tomato fruit development ‘by CO? enrichment. Journal of the American Society for Horricultuml Science. (In pmss.)

. J1 s--- . , c&acts I

Agricultural Rcscarch Organization, The Volcani Center. PI0.B. 6, Bet Dapan, Israel (I-l. linoch ?nd Y. Samish). -

Dcpartmcnt of Botany, TellAviv University, 155 Herzl St., Tc;-Aviv. Israel (Y. B. Samish) Dcpurtmcnt of Vcxctab!e Crops, Cornell Univcrsit)) Ithaca. New York 14850, USA I

(R. Shclldrnko, Jr.) . Division of Agricultural Meteorology, Faculty of Agriculture, Hebgw University

Rehovoh Israel (H. Enoch) 1

Dr.-lng. Rolf Bcttnque. 205.7 Reinbek Bei Hamburg, Klostorbcrgenstr. 53, &nnany Environmcntnl Rdscarch Laboratory, Tucson International Airport, Tucson, *Arizona

85706, USA (C. N. Hodges) Institut fur Ceichte Flachentragwerke, Universitat Stuttgart, 7QoO Stuttgart 80, Germany 9 (F. Otto) Negev Institute for Arid Zone Research, Beer Sheva. Israel (E. Rappaport)

0

i

16-.c Oth& .Prdmisirig c m ter- Conservation Techniques ” ,I 1

Previous chapters have described waterconSQrvatio&kchniques that received I, pecial attention from the panel. Other devilopmentwhowever, may prove to be equally Valuablgin t,he future. Some pos$bilities are briefly desc?-ibed.

Hydrophylic *iI Amendments Y ~ 9 ’

A considerable port&n bf irrigation water -is ordinarily lost because of evapor2tiijn (chapter 8) or because it sinks below the root zone (chap.ter 12). Hydrophylic (water-attracting)- cMmicals can absorb water. holdin it safe from ““evaporation or furtier didipation. Soil mixed wirh ‘such chen!icals .__

comes spongelike, trapping and retaining water for an extended period. *The water is available to plant roots w@ich can draw as required. This method can be particularly important for increasing a e ivater in sandy W‘ soils. Used as soil amendments, hydrophylic chemiw n enhaficc plant

F owth at ldw moisture levels.’ Plant roots and root hairs grow into and

arourid the water-swollen hydEpphylic material and estract water and nutrients from it.

Hydrophylic Chemi6als have been developed that can absorb up to 20 times their dwn weight of water. Although.one such hydrophylic compound is being test-marketed in the Uniied States, tiey‘ are still basically exerimental. -

‘2 The wat.er-holding capacity of ‘&dy soils, clan also be improved ?>y incorporating about 5 percenl of crushed brown coal into the surface layer. This. csn,,dwblc the available moiiture,*promotc uniform soil tcmpcruturcs, and nwturc crops earlieri4” (See Fl6URE 77.) **

Thb very recent dcvelopmeqt of hydrophilic starch copolymers (“super Slurpers’l) that absorb water up t,o l,!ioO times their own weight has been reported. 48 Their role in arid-land $griculture re,mains to be tested.

‘x I

+ 471nformation supplM by Professor A. K. Turner, Department of Civil Engineering, University of Melbourne, Parkville, Victoria 3052, Australia. l

48Reported by Dr. William M. Deane, Northern Regiorul Research Laboratory; U.S. apartment of Agriculture, A.R.S., koria,.IUinois 61604, USA _ / ., 5 -. k .

135

4 #

136 MORE WATER FOR A RID ,LANDS

Artificial Recharge df Underground Rtmvwoirs *

Water removed from un *uife;s can usu--laced by ‘+ natural ‘recharge, but extens s

exceed the replacement. In th ‘; may withdraw enough water to’

cases, surface water can be used to replenish as,artificial recharge. In some places wells-or

e aquifer; elsewhere water isspread on the land, and, unaided s through the soil to the aquifer. This la.~

sed at the surface, pits where they e aquifers are deep. These methods

e a minimum technical expertise for operation areas with appropriate geohydrology are effective.

g interest in artificial recharging of grotindwater because it provides readymade storage reservoirs, free from evaporation and protected ag&t pollution,A and because replenishing groundwater sources keeps neighboring saline waters from $truding.into the aquifer and soil from

OTHER C&SER”ATION TECHNIQ&S \

137

subsiding tito any empty space in a ‘depleted aquifer. It qn also be used to, - reclaim wastewater (&apter 4)Y

Rainwater harvesting (chapter 1) can also be used for recharging ’ groundwater. ‘This is being done experimeritzdly at Wadi Shikmo in Israel. Water collected from a large watershed is permitted to percolate tnto an aquifer to provide increased V’Qter for othetise overextended wells.

lec-td Readings - ’

HycJrophylic Soil Amendr$ents h

*‘Jensen, M. H.; P. A. King; anh R. E&chop. 197 1. A hydrophybc polymer 3s 3 sod amendmqnt, In Proceed@@ of tht? Tenth rational Agricuituml PlustIcs Conjbrcnce.

0 pp. 69-79. (pvailable from Environmental R&arch Laboratory, Unlvcrslty of ’

c Arizona Tucson, Union C~I t#I de Corpo eativc Agriculiural Systems. 197 3. A~clrl~uml Ilydt-ogel

Cdncentrate 5OC. 1 Information. 270 Park Avenue, New York, NY. 10~017. USA. . .

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Artifici$&oundwater Recharge

American Society of CivbEnginccrs; 1961, (;roundwofer hafrn nmnuq-n~~nf.’ A.S.C.E. Manual No. 14. (Available from.American Society of C&i1 Fnglncrcrs, 345 IGst 40th Street, New York, N.L. 10017, L&A.) -

Bianchi, W. C., a&d D.’ C. Muckel. 1970. Ground-w Research Service Pu di cation No. 41-161. (A Agrictilturc, Publications Office, Washington, D.C

International Association df ScientiAd Hydrology 1970 JIIIE~/I~I* Surr,c\3 oj Existing Wuter /?echarge Facilities. Publication NO. 87, Intcrnutlonal Assoclatlon of Scientific Hydrolo&y. 61, rue des Ronczs, Gentbruge, Bclglum

Knapp, G. L., odr 1973. Artificial Recharge of Groundwuter a Bib/lop 73-202. Water Resources Scientific Information Center. cf Rcsourc-zx Research, Department of the Interior. Wdahington, D.C. 20

ignor, D. C,,; D. J. Grotitz; and W. Kam,, 1970. Annotuted I Recharge $ Groundwter, 1955-l 96 7. Water 1990. U.S. ~eolo~ul

, Survey, Department of thg Interior, Reston, Vir Todd, D. K. 1959. Annqtated Bibliogmphy on e of (;roundwater

Through 19.54. Water Supply Paper .!/I?!-. Signor, ct al.) ~

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Lc pres,ent rapport traite de techniques peu connues mais prornetteuses pour

, I’utilisation et al conservation “des ressources aquatiques insuffkantes dans les zones arides. Ce document n’est pas un manuel technique; il vise fi appeler l’attention des

c responsables et chercheurs de I’agriculture du developpement communautaire sur certaines Fssibilites d’exploiter des idees ables et d’une portPe sociale probable- ‘\ ment ClevCe.

11 faut, pour le moment, considerer les techmques expodes comme des adjuvants. et non comme des variantes, aux mtthodes nomrales de foumiturc et d’exploitation de Iteau a grandc Cchelle, Ehes doivent presenter un interet local immediat pour Ic m developpement et Id“ conservation des ressourccs aquatiques a petite Cchelle, surtout . dans Its regions @car-t&es ne disposant que d’un approvisionncmcnt intermittent. Avec dcs recherches et unc adaptation plus pokskes, certaines de ces techniques peuvent s’av&er d’un meritc tconomique concurrentiel i I’tgard des methodes habituellement

* employees pour augmenter l’aliinentation en eau ou pour%duire h4 demandc. L’introduction ‘de ce rapport prtsente brievement un c&sin nombre d’idtes

souvent negligees, qui ont leur importance pour l’exploitation del’eau dans les teks arides. Les chapitres quila suivent traitent de techniques particul.iZres: les chapitres 1 a 6, de celles qui permettent d’augmenter les eaux disponibles; les chapitres 7 $ 16, de celles grlck auxquelles on peut conserver I’eau et r&dune la demande. On trouvera - ensuite un resume! de chaque chnpitre. Y “ c

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- Collecte de I’eu de pluie

I L’eau de pluie recueillie au pied des versants de collines et dws des b&ins

foumir des ressources d’eau supplementaires i has prix et de haute 9 I I

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Agriculture par ruissellement *.

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Elle implique la collecte de l’eau de pluie, mais I’eau e$ utiliske directement darts des systemes agricoles sptkialement conqus i cet effet. I

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lrri&on par aau salbe

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L’eau s&e est facilement disponible, mais on I’utilise rarement parce qu’elle reduit la croissance et le rendement des plantes. II est de plus en plu$SprouvC qu’avec des e precautions, et dans certaines conditions favorables, on peut avantageusement irriguer avec l’eau salee. .

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Remploi cks aaux ‘t _

L’augmentation de la demande en eau im;ose qye I’on &rCilise beaucoup plus I’eau. 11 est possible qu’a I’avenir I’evolution technique {i.ecy-clage et traitement pcrfectionnf des eaux) rev& une ej-ande importance. .-

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0 Puits

Le puits creuse de main d’homme, methode qui renionte i des milhers d’annecs, connait un regain de’pdpularite avec I’aide de nouveaux materiaux et appareils de construction. Les “Qanats” et les puits horizontaux sont des procedes qui permettent de cap&r lea eaux souterraines sans employer de po,mpes. ./--

I Autres sources d’eau et mkhodes da dbction

Dans cc chapitie, on Cvoque npidcmcnt le captagn des caux phrenhques, la dCs isation, la distillation solairc. I’utilnatron des satellites et des av~ons pour le c. reP e de l’eau dans Its terrcs aridcs, I’augmentation de la pluvlosite, la possibilite de 6 SC servir dcs icebergs commc source d’cnu. cnfm. la collcctc de fa r&e et du brouillard.

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Reduction de I’tivaporation des surfaces aquetiques G

Comme I’evaporation est invisible, on la considere rarement comme une drieuse J cause d’epuisement des eaux accumuEes, rn-ais les perks anhuelles dues a I’kaporation, surtout dans les zones arides, spnt considerables. L’abaissement de I’haporation merite qu’on lui pnZte de plus en plus d’attention comme moyen de conserver I’eau.

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Nouveller tachniquw de lutte contre Ias infiltrations

L’infiltration est ?I l’origine de grdves d&perditions d’1’au dans Its canaux et retenues. Les matCriaux et techniques modernes pcuvcnt n!duire ou supprimer I’infiltration, mais les’frais demeurent eleves.

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Fialentissement de l’baporation der surfaces ptiologiques

Cette evaporation provoque une diperdition d’eau mais on peut la diminuer par des “couvertures” ou dechets organiques. Dans ‘&en des cas. ceuxci remplissent Cgalement d’autres roles: arreter la propession du desert ou favor&r l’agriculture par ’ ; ruissellement. .I h,~ 1

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Irrigation par filets d’eau

Cette mCthode rkemment mise au point utilise un sys&ne de tuyaux en matiire plastique p1acCs sur le sol parmi les plantes. L’eau circulant dans les canalisaiiions s’tkoule sur le sol g c6tk de chaque plante i un rythme soigneusement adapt6 aux besoins de la plante. Par rapport A l’irf-igation traditionelle, on a obtenu des rendements agricoles excellents avec’un volume d’eau minimal.

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Autras nouvelles mtWwdes d’irrigation . I

On prksente, au moyen d’illustrations, que;ques mithodes d’inigatio? simples, laisdes de c6tC dans leg ouvrages techniques ou les manuels, et susceptibles de r’en des services dans les terres arides. > s.w

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Alligament das ptwtes d’infiltration l

U y a, dans les zoneskdes, de vastes &endues de terrain sablonneux qui ne servent pas $ I’agriculture parce que I’eau s’enfonce trop rapidement au-dessous d-u niveau des racines et que I’on ne dispose, pas du supplkment d’eau d’irrigation qui permettrait de compenser cette perte. On met actuellement au point des techniques visant i &Cer des

i&es titificielles d’humiditk souterraine ‘~estink i empkher ou i rkduire le ge de I’eau et des ClCments nutritifs. \- I

oix et exploitation das cultures en VW d’une utilisatio I plus rationnelle de I’eau

On n’a pas rMis4 grand chose en. fait -be pro&d& de cukure permettant d’utiliser ‘eau dans les terres arides. Be$ucoup de possibilitks de recherche restent

i explorer, de la &nCtique phytologique i la technologie.

Rkbtion de la transpy-1 * *

Environ 99 pour ‘100 de l’eau &&bCe par les racines des planks est lit&C dans I’$r par les surfaces des fe&lles. Si I’on peut trouver des moyens pratiqties de rCduire . ce phenomke, on parviendria i tialiser d’&ormks Cconqies dans le volume d’eau . nkessaire ii la culture d’une plante donnCe.

Agriculture en milieu surveilk I .

En cultivant les plantes dans’*des compartiments btanches mals transparents. on pcut beaucoup diminucr la quantiti’d’eau normalement perdue, et on peut aussi rigler I’atmosptke, autour des plantes, dc manikre 2 porter la productivik au maximum. Ce sont Iri dcs m~thodes cotitpuses, mais qui permettent d’atteindreun rendement agricole 6lev6 avcc de petites qutlntitks d’eau..

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Autres techniques prometteutes de conservation de I’eau -\

Ce chipitre aborde briivement les amiliorations pCdologiques qui favorisent la ‘conservation de I’eag, et la reconstitution artificielle de,s rkerves phrkatiques.

I Espiiiol

Estc Informc SC rcficrc a .tecnolGgias poco conocidas &rr, quc ufreccn buenas “posibilid riridas.

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des para cl uso y conscrvacion de 10s cscasos recursos de agua cn regiones o es un manual tknico, su propC&to es Ilamar la atcncltin de funclonarlos c

UlV igadorcs intcrcsados en cl deSarrollo agricola y comunal svbrc oportunldadcs de guir conceptos bicn fundados que pucden tener un probable alto valor social

Las teorias expuestas dcbcn considerarse, por ahora, mas blen ctimo complemcrl)os que substitutes de mCtodos not-males-:be suminlstro y adminlstracl6n de aguas. ‘-_ Deberan consti n valvr local mmctiato en cuanto al &sarrollo y conservac1on dc aguas en pequc ala. cspccialmentc eh regloncs rcmotas dondc la provIsiOn de ague cs intcrmitcntc. (‘on mris investigaclOn y adaptaclbn, algunas tecnologlns pucdcn

P cmostrar quc pucdcn competlr econbmramcntc con 10s mtitodus normalcs para Ilumcntcr cl sumlnistro de u rcduclr la dcmanda.

En cstc informc sc pr tan brcvcmcntc v;lnos conccptos. a menudo no tcnldos en cuenta. .pcro quc son i rtantcs para la adminutracibn dc aguas en tlcrras clrld,as En 10s CilpitUlUS siguicntc xponcn tknologias cspccificas. Los capitulos I al b se refiercn il tee ogias para‘ n?]onr cl sumlnlstro de aggas’ ) IUS capitulus 7 al 16 a tknologias p reducir la dcmanda. A contlnuacion SC hacc un Inf~~rmc dc cada 0 capitulo.

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Rxoleccibh de agua de lluvia % E\ agua de lluyia recogida de las laderas de 10s montes y 10s coktor ethos a

mano pucden rcprcscntar nucvas fucntes de agua de bajo costo y buena c ad para ticrras riridas.

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Agricultura de derramemiento .

La agricultura dc dcrramamlento rcqulcre la recolccclOn de agua dc Iluv~a peru cl I’

; agua se usa dircctamentc en slstcmas agricolas d~serladus especlficamcnte al efecto

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Regadio con agua salina : .

El agua salada es fricil de obtencr ampljamentc pero se utiliza raramente-dcedldo a quc rcstringe el crecimiento y I9 produccibn de*las plantas. Actualmente se est2

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acumulandB evidencia quc con cuidado y bajo ciertas condicionc; favorables se puede utilizar agua salada bencficiosamcntc para regadio.

Reutilizaciirn de aguas

La crecicnte demandaPe sumnistro de aguas impone la necesrdad de aumentar al mkimo la reutilization de las aguas. Los dcsarrollos tecnicos. tales coma el recrclaje y cl tratamrento de aguas de albanal pueden tener gran rmportancla en el future

Pozos .

1: Los pozos excavados a man’o, una technologia que comenzb miles de silos atras,

csti volvicndo a ganar popularidad con la ayuda de nuev 3 s materiajes y equrpo de construction. Los pozos “Qanats” y honzontales son metodos dc derivacrljn de agus subterraneas sin u tilizar bombas.

Otras fuentes de aguas y titodos de ckeccion de agua _

En estc capitulo se hate una breve mention a la “mineria” de agtias sudterraneas, ‘dcsalinizacion, dcstilacion, utilizacron dc satelites y act-or-raves para detectar fuentcs de aguas en tierras aridas, incrcmcnto de Iluvras, la posibilrdad de uttlear ,tCmpanos de hiclo coma fucntcs de agua y la recoleccron de rocio y nicbla.

Reducckn de la evaporacibn de las aquas de superficie “,

Debido a gut la cvap@cibn es invisible. con frecuencia no se considera un problcma grave de mcrma cn las aguas almaccnadas, pero Ias p4rdrdasanuales debrdas a la evaporation, especialmentc en ticrras riridas son enohncs.’ La reduccibn de la evaporation mcrece un mayor inter&s coma un medic, para la conservacron de 10s rccursos de aguas.

Nuevas thcnicas ‘para el control de la pesmeabilidad \

La.permeabilidad causa graves perdidas de agua en canales y cmbalses. Utilizando materialcs y ttcnicns modernos se puede reducir o eliminar la pcrmeabilrdad, pcro cl cost0 aun’sigue sicndo muy alto.

Redu&ih de’la evaporacih de’la superflcie del suelo

La cvaporacion de la ‘superficie del suelo representa una perdlda Je agua. pcro se puedc rcducir cubriendo cl suelo concubiertas o capas protettoras En muchos cases las cubiertas sitvcn de funciones complementarias tales como rmpedrr la Invasion del desicrto o la promotion de la agircultura de derramamiento.

Regadio por goteo .

Estc mCtodo de regadio recien dcsarrollado usa un sistcma de tuberiasde pktico colckadas en el suelo entre las plantas. El agua que pass a traves de las tuberias gotea ’

dentro del suelo al lado de cada planta a un r$imen cuidado d rnente calculado en funcion de la’s neccsrdades de las plantas. Comparado con el regadio conventional. con este metodo se han obtenido excelentes rendimientos de cosechas con una ‘ml’nima cantidad de agua. I’ *

Otros novedosos mitodos de regadio .

Se presentan grificamente otros metodos de regaaio simples. no tenidos en cuenta en manualcs ni en libros ttcnicos, que tienen beneficio pot coal para las terrras aridas. s

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Reduccibn de phrdidas por peruhcibn h \ -.

Vastas cxtcnsI~rnes de suclo arcnosdi en trerras artdas no SC uttlrLan para la agricultura dcbrdo a quc cl agua SC cscurrc r dcba)o dc la raiz de la planta dcmasrado ripido y no se dispone del agua necesa par-r. compensar esta falta de repadio. Actualmente se ,xstan desarrollando teen pa& producir una barrera’su6terrzinea artificial para impedir o restringir que el agua $710s nutdentes se pierdan. , ‘“i I

Selecci6n y administracih de corecchm pre u@‘zar el ague nub aficientsmante

Es muy pt)co lo que SC ha hccho para drsenar sntcmas cfictcntcs de aguas para la agrrcullura cn trcrras aridas ‘I‘odavia qucdan por explorar numeros3s oportunrdadcs dcsdc in gcn6tic3 de plantas hasta la ingentcria agricola.

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Reduccibn de la tranrpiracibn

C’erca de un W% dcl agua absorbida por las nices de la planta es devuelta al arrc por las superficrcs de las holas. Si SC pucdcn lograr medros prictrcos para rcducrr cs+tc proctio, SC podrin obtcrier considerables ahorros de agua necesarta para producer una cosecha dctcrminada.

Agricultura de medio ambiente controlado 2

Mediante la \rernhr;r dentro de rccmtus de protcccron. cstanc‘os al, sgua. se purdr roducrr ~ollslll~r;tMcmentc la cantidad dc agua que w perdcria norrnalmente y la atmbsfera alredctlw dc las pl8ltilS se puedc -maneJar parl aumcnttu al niktmo su productwidad. htos SW sislcmas costosos per0 cwn ellos se puide lograr una producttvtdad agricola nIti\ con pequer’las canttdades de ~EUA 1

Otrar tbcnicar de conservacibn de a&~ar pomet&bres

,En cute capitulo se* hate una breve menc’ron a reformas en el suelo ,para tpnservacion de aguas y recarga artificial de deposrtos de agua subterraneos. t

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ADVISORY COMMITTEE ON TECHNOLOGY INNOVATiON \

Members

GEORGE BUGLIARELLO, President, Polytechnic Institute of New Brooklyn, New York, Chairman

- E. R. PARISER, Senior *Research Scientist, Department ot trition and 7 Food Science, Massachusetts Institute of Technology, Carnbri ge, Massa-

chusetts r

LEWIS PERINBAM, Vice President, Canadian- International Development *’ Agency, Ottawa, Canada * .

CHARLES A. ROSEN, Staff Scientist, Stanford Research Instrtute, Menlo Park, California c

, STANISLAW ULAM, Department of Mathematics,. University of Colorado,

Bdulder, Colorado

BOARD ON SCIENCE AND TECHNOLOGY FQR \

INTERNATIONAL DEVELOPMENT $9 -

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embers

CARL DJERASSI, Department of Chemistry, Stanford University, Stanford, California. Chairman

GIlORt~r:, S. HAMMOND, Foreign Secretary, National Academy of Sciences, t2x officio

-RUTH ADAMS, Executive Director, American Civil Liberties Union. Chicago, * Illinois

JOHN D. BALDESCHWIELER, Division of Chemistry and Chemical Engi- ring, California Institute of Technology, Pasadena, California N. BE H R M AN, Professor of International Business. School of Business

ministration, University of North Carolina, Chapel Hill, North Carolina IVAN L. BENNETT, JR., Dean, School of Medicine. New York University e Medical Center, New York, New Yyk

Y b

R. BROWN. &%velop”nient Council. Washington, D.(‘. ent, -Polytechnic Institute of New York,

ormer Vice Pr>sident, International Minerals and Is Corporation, New York, New York R. HEWLETT, President and Chief Executive qfficer. Hewlett-

rd Company, Palo Aito’,daIifornia ident, Arthur D. Little, Inc., Cambridge,

FRANKLI-N A. LONG, j’rogram on*Science, Technology, and Society, Cornell University, Ithac8, New York

JOSEPH PETTIT, President, Georgia Institute of’ Technology, Atlanta.. Georgia

JOSEPH B. PLATT; President, $-huvey Mudd College, Claremont,. California HELEN RANNEY, Chairman, Department of Medicine, University Hospital,

San Diego, California ROBERT M. WALKER, McDoflnell Professor of Physics, Director, Labora- ‘. tory of Space Physics, Washington University, St. Louis, Missouri * GILBERT F. WI-IITE, Institute of Behavioral Science, University of Colorado.

Boulder, Colorado STERLING WORThiN, Vice Pres Gc&

New York . ” efeller Foundation, New York, ’ I.

, Staff

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VICTOR RABINOWITCH, Difector

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BOARD ON SCIENCE AN CHNOLOGY -FOR .

INTERNATIONAL DEVELOPMENT il --

COMMISSION ON INTERNATIONAL RELATIONS NATIONAL ACADEMY OF SCIENCES-NATIONAL R~ESEARCH COUNCIL 2101 Consthtion Avenue, Washington, D.C. 20418, USA .- A

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ADVISORY STUDIES ANdSPEClgL REPQRTS

PUBLISHED 1

Q& 1. East Pakistan .ia’nd and Water Development &s Related to Aficuiture. January 1971. 67 p. (out of print) RCVICW~ World Bank proposed tictlon

._ program in land and water management. N-TIS Acaalon No. PB, 203-328.

2. The International Development Institute, July 1971. S7. p. Endorses concept of new science-based technical assistance agency as~~ccessor to

\ AID; examines its character, purposes, and t‘unctlons. 2 3. Solar l+rgy in Developing CountriF; Perspectives and Prospects. !&arch

19’72. 49 p. (out of print) Assesses state of art, acntlfics promlslng areas for R & D, and proposes multipurpose regjonal energy rcscarch Institute

@:” (

for developing world. NTlS A ccession No. PB 208-550. 54.50 l

4. Scientific and Technic+ Iriformntign for De,tloping Countries. Apnl 1972. 80 p. (out of print) Examines problems of developing world’s _

. ‘access to scienific sod te’chnital informatlon sources, provides ratlondc _ for assistan&. @ this field, and suggests programs for strcngthcning

information infrastruc re and promoting &formatlon transfer. NTIS Accession No. PB 2 1 O- i .

- 6.. Research Management ‘knd Technical En,trepreneurship: A 5.S. Role in I Improving mq in Developing CoUntlies. 1973. 40 p. Recommends a

~ ’ initiation of a systematic prognm and indicates priority elements.

I 7. U.S. International Firms and R, D & E in Dewloping”Iountries. 1973. 92 : p. Discusses aims and interests of lnternatiopal firms and dc~eloping-

country hosts and suggests that differences could bc Illitlgated by sustained efforts by the firms to strengthen lowI R, D & E-capabllitics.

8. Ferrocement: Appbtions in Developing Cowtries. 1973. X9 p. .Asscsses s.tate of the art and ci’tes applications of particular interest to developing countries-boatbuijding, ‘construction, food- and water-storage facilities, etc. a

9. Mosquito Control: Some Perspectives for Developing Ckntrie~. 1973. 63 p. Examines biologi&&ontrol es .to conventional pesticides; evahates state of knowledge potential of several approaches. - 1.

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10. Food *Science b Developing Countriek A Selection of Unso#lve”d . Ptot$ms. 1974. 81 p. Describes 42 unsolved technical problems with

und in f ormation,’ possible approaches to a’solution, and informa- ,

d Management: Some Perspective; for Guyana. 1973. 44 p. 4

Report of workshop ~4th the. fiational Science *Research Council of Guyana- describes new methods of aquatic weed conirol suitable for tropical developing countries.. ‘5

12. Roofing in Developing Countries: Research for New Technoibgies. 193’4. Emphasizes- the need for research on low cost roofs, particularly using materials available in devclo ing eoun tries.

13. teting the Challenge of ndustrialization: A Feasibili~~f an f Intematlorial industrialization Institute. 1973. 133 p. Advances concept of an independent, interdisci{linG research institute to illuminate new policy options confronting all nations.

14. More Water for Arid Lands: Promising Technologies and RCsenrch Opportunities. 1974.

15. lntemational Development Programs of the Office of th,e Foreign P

k4 Secretary, by Harrison Brown and irlcrcsa Tcllcz. 1973. hS p. lIisto;y and analysis, 1963-l 972tiists staff/participants and publlcabons.

“fN. PREPPRATION (Working Titles) .

5. The Role 0fJJ.S. Engineering Schools in Foreign Assistance Actlvltlcs 16. Neglected Tropical Plants with Promising Economic Value

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26 More Water a jRid Lands

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