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Alkali soil

  (Redirected from Alkali soils)

Alkali, or alkaline, soils are clay soils with high  pH (> 8.5), a poor soil structure and a lowinfiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 etre depth. !l"ali soils

owe their unfavora#le physico$cheical properties ainly to the doinating presence of sodiucar#onate which causes the soil to swell%1& and difficult to clarify'settle. hey derive their naefro the al"ali etal group of eleents to which the sodiu #elongs and that can induce #asicity. oeties these soils are also referred to as (alkaline) sodic soils.!l"aline soils are #asic, #ut not all #asic soils are al"aline, see* +difference #etween al"ali and #ase+

Rice cultivation / paddyeld in alkali soils

Contents

• 1 Causes

• 2 Agricultural problems

• 3 Cemistry

• ! "olutions

• # $eacing saline sodic soils

• % "ee also

• & References

Causeshe causes of soil al"alinity are natural or they can #e an$ade.

1' e natural cause is te presence of soil minerals producing sodiumcarbonate (a2C*3) and sodium bicarbonate (a+C*3) upon ,eatering'

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2' Coal red boilers / po,er plants ,en using coal or lignite ric in limestone produces as containing calcium o-ide (Ca*)' Ca* readily dissolves in ,aterto form slaked lime / Ca(*+)2 and carried by rain ,ater to rivers / irrigation,ater' $ime softening process precipitates Ca and .g ions / removesardness in te ,ater and also converts sodium bicarbonates in river ,aterinto sodium carbonate'20 "odium carbonates (,asing soda) furter reacts

,it te remaining Ca and .g in te ,ater to remove / precipitate te totalardness' Also ,ater soluble sodium salts present in te as enance tesodium content in ,ater' e global coal consumption is && million tons inte year 211' us river ,ater is made devoid of Ca and .g ions andenanced a by coal red boilers'

3' .any sodium salts are used in industrial and domestic applications suc as"odium carbonate "odium bicarbonate (baking soda) "odium sulpate"odium ydro-ide (caustic soda) "odium ypoclorite (bleacing po,der)etc' in uge uantities' ese salts are mainly produced from "odium cloride(common salt)' All te sodium in tese salts enter into te river / ground,ater during teir production process or consumption enancing ,atersodicity' e total global consumption of sodium cloride is 2& million tons inte year 21' is is nearly eual to te salt load in te migty Ama4onRiver' .anmade sodium salts contribution is nearly &5 of total salt load of allte rivers'30 "odium salt load problem aggravates in te do,nstream ofintensively cultivated river basins located in Cina 6ndia 7gypt 8akistan,est Asia Australia ,estern 9"A etc' due to accumulation of salts in teremaining ,ater after meeting various transpiration and evaporation losses' !0

!' Anoter source of man made sodium salts addition to te agriculture elds /land mass is in te vicinity of te ,et cooling to,ers using sea ,ater todissipate ,aste eat generated in various industries located near te seacoast' +uge capacity cooling to,ers are installed in oil reneriespetrocemical comple-es fertili4er plants cemical plants nuclear : termalpo,er stations centrali4ed +;AC systems etc' e drift / ne dropletsemitted from te cooling to,ers contain nearly %5 sodium cloride ,ic,ould deposit on te vicinity areas' is problem aggravates ,ere tenational pollution control norms are not imposed or not implemented tominimi4e te drift emissions to te best industrial norm for te sea ,aterbased ,et cooling to,ers'#0

#' e man<made cause is te application of soft ,ater in irrigation (surface orground ,ater) containing relatively ig proportion of sodium bicarbonates and less calcium and magnesium'10

Agricultural problems!l"aline soils are difficult to ta"e into agricultural production. ue to the low infiltrationcapacity, rain water stagnates on the soil easily and, in dry periods, cultivation is hardly possi#lewithout copius irrigated water and good drainage. !griculture is liited to crops tolerant tosurface waterlogging (e.g. rice, grasses) and the productivity is low.

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Cemistryoil al"alinity is associated with the presence of sodiu car#onate or washing soda (-a/O) inthe soil,%& either as a result of natural weathering of the soil particles or #rought in #y irrigationand'or flood water.

he sodiu car#onate, when dissolved in water, dissociates into -a2 (two sodiu cations, i.e.ions with a positive electric charge) and /O

3 (a car#onate anion, i.e. an ion with a dou#lenegative electric charge).

he sodiu car#onate can react with water to produce car#on dio4ide (/O), escaping as a gas or o#sor#ed #y !lgae, and sodiu hydro4ide (-a2OH  ), which is al"aline (or rather #asic) andgives high pH values (pH>8.5).%&

Notes=

• >ater (+2*) is partly dissociated into +3*? (ydronium) and *+@ (ydro-yl) ions' e ion +3*? as a positive electric carge (?) and teydro-yl group *+@ as a negative carge (@)' 6n pure neutral ,aterte concentration of +3*? and *+@ ions euals 1@& e/l eac(respectively 1-1@& g/l and 1&-1@& g/l) very small concentrations'

• 1 e B 1 euivalent ,eigt corresponds to as many grams of tesubstance as its formula ,eigt divided by its valence' 6t is also kno,nas gram-molecule or mole per unit of valence' or te ydronium ion (+3*?) te formula ,eigt euals 1 and for te ydro-yl group (*+ @)it euals 1&'

•

6n neutral ,ater te p+ being te negative log value of te +3*?

 concentration in e/l is &' "imilarly te p*+ is also &' 7ac unitdecrease in p+ indicates a tenfold increase of te + 3*? concentration'"imilarly eac unit increase in p+ indicates a tenfold increase of te*+@ concentration'

• 6n ,ater ,it dissolved salts te concentrations of te +3*? y *+@ ionsmay cange but teir sum remains constant namely & ? & B 1!' A p+of & terefore corresponds to a p*+ of & and a p+ of ,it a p*+ of#'

• ormally it deserves preference to e-press te ion concentrations in

terms of cemical activity but tis does ardly aDect te value of p+'

• >ater ,it e-cess +3*? ions is called acid (p+ E &) and ,ater ,ite-cess *+@ ions is called alkaline or rater basic (p+ F &)' "oil moisture,it p+ E ! is called very acid and ,it p+ F 1 very alkaline (basic)'

he reaction #etween -a/O and HO can #e represented as follows*

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• 2a? ? C*32G ? 2+? ? 2*+@ BF 2a? ? 2*+@ ? +2C*3

he acid H/O is unsta#le and produces HO (water) and /O (car#on dio4ide gas, escapinginto the atosphere). his e4plains the reaining al"alinity (or rather #asicity) in the for ofsolu#le sodiu hydro4ide and the high pH or low  pOH.

 -ot all sodiu car#onate follows the a#ove cheical reaction. he reaining sodiu car#onate,and hence the presence of /O

3 ions, causes /a/O (which is only slightly solu#le) to precipitate as solid calciu car#onate (liestone). Hence, the calciu ions /a22 are io#ili6ed.

"odium e-cange process bet,een ions adsorbed at te surface of clay particles

and tose in te soil moisture

he presence of a#undant -a2 ions in the soil solution and the precipitation of /a22 ions as asolid ineral causes the clay particles, which have negative electric charges along their surfaces,to adsor# ore -a2 in the diffuse adsorption zone (DAZ, see figure, officially called diffuse

double layer %7&) and, in e4change, release /a22, #y which their exchangeable sodium percentage (ESP) is increased as illustrated in the figure.

 -a2 is ore o#ile and has a saller electric charge than /a22 so that the thic"ness of the !increases as ore sodiu is present. he thic"ness is also influenced #y the total concentrationof ions in the soil oisture in the sense that higher concentrations cause the ! 6one to shrin".

/lay particles with considera#le 9: (> 1), in contact with non$saline soil oisture have ane4panded ! 6one and the soil swells (dispersion).%7& he phenoenon results in deteriorationof the soil structure, and especially crust foration and copaction of the top layer. Hence theinfiltration capacity of the soil and the water availa#ility in the soil is reduced, whereas thesurface$water$logging or runoff is increased. eedling eergence and crop production are #adly

affected.

Note=

• 9nder saline conditions te many ions in te soil solution counteractte s,elling of te soil so tat saline soils usually do not aveunfavorable pysical properties' Alkaline soils, in principle, are notsaline since the alkalinity problem is worse as the salinity is less.

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!l"alinity pro#les are ore pronounced in clay soils than in loay, silty or sandy soils. heclay soils containing ontorillonite or sectite (swelling clays) are ore su#;ect to al"alinity pro#les than illite or "aolinite clay soils. he reason is that the forer types of clay have largerspecific surface areas (i.e. the surface area of the soil particles divided #y their volue) andhigher cation e4change capacity (/9/).

Note=

• Certain clay minerals ,it almost 15 7"8 (i'e' almost fully sodiumsaturated) are called bentonite ,ic is used in civil engineering toplace impermeable curtains in te soil e'g' belo, dams to preventseepage of ,ater'

he <uality of the irrigation water in relation to the al"alinity ha6ard is e4pressed #y thefollowing two inde4es*

1) he sodiu adsorption ratio (!=,%& )

he forula for calculating sodiu adsorption ratio is*

  %-a2& -a2'?!= @ AAAAAAAAAAAAA @ AAAAAAAAAAAAAA   B%/a22' 2 Cg22'& B/a22'D0 2 Cg22'D?

where* % & stands for concentration in illie<uivalents'liter (#riefly e<'l), and ? stands forconcentration in g'l.

Et is seen that Cg (Cagnesiu) is thought to play a siilar role as /a (/alciu).

he != should not #e uch higher than 0 and prefera#ly less than 10F

Ghen the soil has #een e4posed to water with a certain != value for soe tie, the 9: valuetends to #ecoe a#out e<ual to the != value.

) he residual sodiu car#onate (=/, e<'l,%&)*

he forula for calculating residual sodiu car#onate is*

R"C B +C*3@ ? C*3

B0 G Ca??? .g??0

  @ H/O  '1 2 /O

@'0? 3 /a22'0 2 Cg22'1?

which ust not #e uch higher than 1 and prefera#ly less than 0.5.

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he a#ove e4pression recogni6es the presence of   #icar#onates (H/O  ), the for in which ost

car#onates are dissolved.

Ghile calculating != and =/, the water <uality present at the root 6one of the crop should #econsidered which would ta"e into account the leaching factor in the field.%8& he partial pressure

of dissolved /O at the plants root 6one also decides the /alciu present in dissolved for in thefield water. ! follows the ad;usted != %I& for calculating water sodicity.

"olutions!l"aline soils with solid /a/O can #e reclaied with grass cultures, organic copost, wastehair ' feathers, organic gar#age, waste paper, etc. ensuring the incorporation of uch acidifyingaterial (inorganic or organic aterial) into the soil, and enhancing dissolved /a in the fieldwater #y releasing /O gas.%10& eep plowing and incorporating the calcareous su#soil into thetop soil also helps.

Cany ties saltsJ igration to the top soil ta"es place fro the underground water sources rather than surface sources.%11& Ghere the underground water ta#le is high and the land is su#;ected tohigh solar radiation, ground water oo6es to the land surface due to capillary action and getsevaporated leaving the dissolved salts in the top layer of the soil. Ghere the underground watercontains high salts, it leads to acute salinity pro#le. his pro#le can #e reduced #y applyingulch to the land. sing poly$houses during suer for cultivating vegeta#les'crops is alsoadvised to itigate soil salinity and conserve water ' soil oisture. :oly$houses filter the intensesuer solar radiation in tropical countries to save the plants fro water stress and leaf #urns.

Ghere the ground water <uality is not al"aline ' saline and ground water ta#le is high, salts #uildup in the soil can #e averted #y using the land throughout the year for growing plantation trees ' peranent crops with the help of lift irrigation. Ghen the ground water is used at re<uiredleaching factor, the salts in the soil would not #uild up.

:lowing the field soon after cutting the crop is also advised to prevent salt igration to the topsoil and conserve the soil oisture during the intense suer onths. his is done to #rea" thecapillary pores in the soil to prevent water reaching the surface of the soil.

/lay soils in high annual rain fall (ore than 100 c) areas do not generally suffer fro highal"alinity as the rain water runoff is a#le to reduce'leach the soil salts to coforta#le levels if proper rain water harvesting ethods are followed. En soe agricultural areas, the use of

su#surface +tile lines+ are used to facilitate drainage and leach salts. /ontinuous rip irrigation would lead to al"ali soils foration in the a#sence of leaching ' drainage water fro the field.

Et is also possi#le to reclai al"aline soils #y adding acidifying inerals li"e pyrite or cheaperalu or !luiniu sulfate.

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!lternatively, gypsu (calciu sulfate, /aOD. HO) can also #e applied as a source of /a22 ions to replace the sodiu at the e4change cople4.%10& Kypsu also reacts with sodiucar#onate to convert into sodiu sulphate which is a neutral salt and does not contri#ute to high pH. here ust #e enough natural drainage to the underground, or else an artificial su#surfacedrainage syste ust #e present, to perit leaching of the e4cess sodiu #y percolation of  rain 

and'or irrigation water through the soil profile.

/alciu /hloride is also used to reclai al"ali soils. /a/l converts -a/O into -a/l precipitating /a/O. -a/l is drained off #y leaching water. pent acids (H/l, HOD, etc.) canalso #e used to reduce the e4cess -a/O in the soil.

Ghere urea is ade availa#le cheaply to farers, it is also used to reduce the soil al"alinity 'salinity priarily.%1& he -HD (!oniu) present in urea which is a wea" cation releases thestrong cation -a fro the soil structure into water. hus al"ali soils a#sor# ' consue ore ureacopared to other soils.

o reclai the soils copletely one needs prohi#itively high doses of aendents. Cost effortsare therefore directed to iproving the top layer only (say the first 10 c of the soils), as the toplayer is ost sensitive to deterioration of the soil structure.%10& he treatents, however, need to #e repeated in a few (say 5) years tie.rees ' plants follow gravitropis. Et is difficult to survivein al"ali soils for the trees with deeper  rooting syste which can #e ore than 0 eters deep ingood non$al"ali soils.

Et will #e iportant to refrain fro irrigation (ground water or surface water) with poor <ualitywater.

One way of reducing sodiu car#onate is to cultivate glasswort or  saltwort or #arilla plants.%1& hese plants se<uester the sodiu car#onate they a#sor# fro al"ali soil into their tissues. heash of these plants contains good <uantity of sodiu car#onate which can #e coerciallye4tracted and used in place of sodiu car#onate derived fro coon salt which is highlyenergy intensive process. hus al"ali lands deterioration can #e chec"ed #y cultivating #arilla plants which can serve as food source, #ioass fuel and raw aterial for soda ash and potash,etc.

8osporus soil components in relation to soil p+

>ater Availability in relation to "oil p+urter information= >ater content and >ater potential

Hetermining p+Cethods of deterining pH include*

• *bservation of soil prole= Certain prole caracteristics can be indicators ofeiter acid saline or sodic conditions' "trongly acidic soils often ave poorincorporation of te organic surface layer ,it te underlying mineral layer'

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 e mineral ori4ons are distinctively layered in many cases ,it a paleeluvial (7) ori4on beneat te organic surfaceI tis 7 is underlain by a darkerJ ori4on in a classic pod4ol ori4on seuence' is is a very roug gauge ofacidity as tere is no correlation bet,een tickness of te 7 and soil p+' 7ori4ons a fe, feet tick in lorida usually ave p+ Kust above # (merelyLstrongly acidL) ,ile 7 ori4ons a fe, inces tick in e, 7ngland are

Le-tremely acidL ,it p+ readings of !'# or belo,'1020 30 6n te souternJlue Ridge .ountains tere are Lultra acidL soils p+ belo, 3'# ,ic aveno 7 ori4on'!0 8resence of a calice layer indicates te presence of calciumcarbonates ,ic are present in alkaline conditions' Also columnar structurecan be an indicator of sodic condition'10

• *bservation of predominant Mora' Calcifuge plants (tose tat prefer anacidic soil) include Erica Rhododendron and nearly all oter 7ricaceae species many birc (Betula) fo-glove (Digitalis) gorse (Ule  spp') and "cots8ine (!inus syl"estris)' Calcicole (lime loving) plants include as trees(#rainus spp') oneysuckle ($onicera) Buddle%a dog,oods (&ornus spp')lilac ('yringa) and &lematis species'

• 9se of an ine-pensive p+ testing kit ,ere in a small sample of soil is mi-ed,it indicator solution ,ic canges colour according to teacidity/alkalinity'

• 9se of litmus paper' A small sample of soil is mi-ed ,it distilled ,ater into,ic a strip of litmus paper is inserted' 6f te soil is acidic te paper turnsred if alkaline blue'

• 9se of a commercially available electronic p+ meter in ,ic a rod isinserted into moistened soil and measures te concentration of ydrogen

ions'

7-amples of plant p+ preferences is section possibly contains original research' 8lease improve it by

verifying te claims made and adding inline citations' "tatements consisting

only of original researc sould be removed' (No"ember )*+*

• p+ !'#@#'= 7ricaceae (A4alea Jilberry Jlueberry Cranberry+eaterdisambiguation needed0) +ydrangea for blue (less acidic for pink)$iuidambar or ",eet Num *rcid 8in *akcitation needed0

• p+ #'@#'#= Joronia Hapne 7ricaceae= (Camellia +eaterdisambiguation needed0Rododendron) erns 6ris *rcids 8arsley Conifers (e'g' 8ine) 8oaceae=(.ai4e .illet Rye *at) Radis "olanales= (8otato ",eet potato)Jromeliaceae (8ineapple)'110

• p+ #'#@%'= Asteraceae= (Aster 7ndive) Jrassicaceae= (Jrussels sproutOolrabi) Carrot Cucurbitales= (Jegonia Cayote or Coko) abaceae=(Jean Crimson Clover 8eanut "oybean) 8etunia Rubarb ;iolet most

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bulbs (Canna HaDodil Ponuil) $arkspurdisambiguation needed0 8rimrosedisambiguation

needed0

• p+ %'@%'# Antirrinum or "napdragon Jrassicaceae= (Jroccoli CabbageCandytuft CauliMo,er urnip >allMo,er) Cucurbitaceae= (Cucumber8umpkin "uas) abaceae= (8ea Red Clover >ite Clover) Nladiolus

6celand 8oppy Rosales= (Cannabis Rose "tra,berry) "olanaceae= (7ggplantor Aubergine omato) ",eet corn ;iolaceae= (8ansy ;iola) Qinnia or Qinnea

• p+ %'#@&'= Amarantaceae= (Jeet "pinac) Apiaceae= (Celery 8arsnip)Asparagales= (Asparagus *nion) Asteraceae= (Crysantemum Halia$ettuce) Carnation abaceae= (Alfalfa ",eet pea) .elon "tockdisambiguation

needed0 ulip

• p+ &'1@' $ilac

Canging soil p+

6ncreasing p+ of acidic soil

he ost coon aendent to increase soil pH is lie (/a/O or Cg/O), usually in thefor of finely ground agricultural lie. he aount of lie needed to change pH is deterined #y the esh si6e of the lie (how finely it is ground)and the #uffering capacity of the soil. !high esh si6e (0100) indicates a finely ground lie, that will react <uic"ly with soil acidity.Luffering capacity of soils is a function of a soils cation e4change capacity, which is in turndeterined #y the clay content of the soil, the type of clay and the aount of organic atter present. oils with high clay content, particularly shrin"swell clay, will have a higher #ufferingcapacity than soils with little clay. oils with high organic atter will also have a higher #uffering capacity than those with low organic atter. oils with high #uffering capacity re<uire

a greater aount of lie to #e added than a soil with a lower #uffering capacity for the saeincreental change in pH.Other aendents that can #e used to increase the pH of soil include wood ash, industrial /aO(#urnt lie), and oyster shells. Ghite firewood ash includes etal salts which are iportant for processes re<uiring ions such as -a2 (sodiu), M 2 (potassiu), /a2 (calciu), which ay oray not #e good for the select flora, #ut decreases the acidic <uality of soil.hese products increase the pH of soils through the reaction of /O

3 with H2 to produce /O and HO. /alciu silicate neutrali6es active acidity in the soil #y reoving free hydrogen ions,there#y increasing pH. !s its silicate anion captures H2 ions (raising the pH), it forsonosilicic acid (HDiOD), a neutral solute.

Hecreasing p+ of alkaline soil

• 6ron sulpates or aluminium sulpate as ,ell as elemental sulfur (") reducep+ troug te formation of sulfuric acid'

• 9rea urea pospate ammonium nitrate ammonium pospatesammonium sulpate and monopotassium pospate fertili4ers'

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• organic matter in te form of plant litter compost and manure ,ill decreasesoil p+ troug te decomposition process' Certain acid organic matter sucas pine needles pine sa,dust and acid peat are eDective at reducing p+' 120

"ee also

• Alkali soils

• Cation<e-cange capacity

• ertili4er

• $iming (soil)

• *rganic gardening

• "oil conservation

• Acid mine drainage

• Acid sulfate soil

• "oil type

References

1'

  8erry $eonard' Lp+ for te NardenL' Retrieved 11 Hecember 212'

"oil "urvey Hivision "taD' L"oil survey manual'13' Capter 3 selected

cemical properties'L' "oil Conservation "ervice' 9'"' Hepartment of Agriculture

+andbook 1' Retrieved 211<3<12'

"parks HonaldI 7nvironmental "oil Cemistry' 23 Academic 8ress $ondon

9O

ttp=//edis'ifas'uM'edu/c% 

inck Arnold (1&%)' !anenern/hrung in 'tichworten' Oiel= +irt' p' '

6"J 3<##!<1&<%'

Jrady ' and >eil R' e ature and 8roperties of "oils' 13t ed' 22

+ansson et al (211) HiDerences in soil properties in adKacent stands of "cots

pine or,ay spruce and silver birc in "> ",eden' orest 7cology and

.anagement 2%2 #22@#3

Rout NRI "amantaray "I Has 8 (21)' LAluminium to-icity in plants= a

revie,L' Agronomie 21 (1)= !@#' doi=1'1#1/agro=211#' Retrieved 11 Pune 21!'

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  ttp=//,,,'e-tension'org/pages/&#/soil<p<and<nutrient<availability  

Juol "' >' R' P' "outard R'C' Nraam and 8'A' .cHaniel' "oil Nenesis and

Classication' (#t) 7dition 6a' "tate 8ress p' !!' 22

ttp=//,,,2'a,aii'edu/Snv

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