Water use, productivity and forage quality of thehalophyte Atriplex nummularia grown on saline

waste water in a desert environment

Edward Glenn*, Rene Tanner*, Seiichi Miyamoto†,Kevin Fitzsimmons* & John Boyer‡

*Environmental Research Laboratory, 2601 East Airport Drive, Tucson,Arizona 85706, U.S.A.

†Texas Agricultural Experiment Station, 1380 Texas A & M Circle, ElPaso, Texas 79927, U.S.A.

‡Arizona Public Services, Inc., P.O. Box 53999, Mail Station 9368,Phoenix, Arizona 85072-3999, U.S.A.

(Received 29 June 1997, accepted 9 September 1997)

The halophyte Atriplex nummularia Lindl. was grown in a desert climate inTempe, AZ, for 3 years in outdoor drainage lysimeters. Plants were irrigatedwith two sources of waste water from an electric power plant: mildly saline(1149 mg l–1 total dissolved solids (TDS)) storm runoff collected in a pond, orbrackish (4100 mgl –1 TDS) blowdown water from cooling towers. Plantswere irrigated weekly with enough water to replace evapo-transpiration lossesbut leaching fractions were only 4–10%. Atriplex nummularia performedequally well on both water sources, even though soil solution salinity in therooting depth profile ranged from 300–1000 mol m–3 NaCl in lysimetersirrigated with blowdown water compared to only 40–90 mol m–3 in lysimetersirrigated with pond water. Atriplex nummularia had higher productivity, wateruse efficiency and consumptive water use than conventional forage crops inArizona irrigation districts. Nutritional content of plant tissues was acceptablefor use as a ruminant forage. Atriplex nummularia had key traits desired in aplant for disposal of saline water: high consumptive use to minimize land areadevoted to reuse; high salt tolerance, conferring the ability to grow under lowleaching fraction to minimize discharge to the aquifer; and usefulproduction.

©1998 Academic Press Limited

Keywords: Atriplex; saline irrigation; salt stress; evapo-transpiration;drainage water management; halophyte

Introduction

Finding methods for the safe and economical disposal of saline water is a challengingtask when the volume involved is large, such as drainage water from irrigatedagriculture in arid and semi-arid areas (Westcott, 1988; Ayars et al., 1993). A similarproblem on a smaller scale confronts industrial generators of brine, such as electric

Journal of Arid Environments (1998) 38: 45–62

0140–1963/98/010045 + 18 $25.00/0/ae970320 © 1998 Academic Press Limited

power plants that produce saline blowdown water from the cooling process (Engel etal., 1985a,b). Discharge of brine into rivers, canals and municipal sewer systems cancreate a salinity hazard for downstream water users. This is especially true in inlandarid regions which do not have large receiving bodies of water into which brine can bediluted. On the other hand, isolating the brine in evaporation ponds is becominguntenable due to the evapoconcentration and biomagnification of toxic elements suchas selenium in food chains (Ong & Tanji, 1993; Presser, 1994; Ong et al., 1995). Theuse of brines to produce salt-tolerant crops near the point of generation is a realisticoption for handling saline waste water flows (Westcott, 1988; Rhoades et al., 1989;Riley et al., 1997).

An ideal plant for recycling brines would have extremely high salt tolerance, allowingit to be grown on a low leaching fraction to minimize the subsequent volume ofsubsurface drainage that must be handled; high consumptive water use, minimizingthe amount of land that must be devoted to recycling brine; and economic value, to atleast partially repay the cost of production. Atriplex spp. are known to have high salttolerance (e.g. Glenn et al., 1997), high water use efficiency (WUE) (e.g. Miyamoto &Mueller, 1994) and acceptable nutritional content when used as animal fodder (e.g.Swingle et al., 1996). Atriplex and other halophytes have been tested as irrigated crops(Watson, 1990; Watson & O’Leary, 1993; Watson et al., 1994; Glenn et al., 1997) andwere included in the agroforestry plantings to reuse drain water in the San JoaquinValley (Watson, 1990; Watson & O’Leary, 1993).

We tested the suitability of Atriplex nummularia Lindl. for the reuse of cooling towerblowdown and site drainage at an electric power plant in Arizona. In using Atriplex fordisposal of blowdown water, the primary concerns are: (i) the extent of evaporativewater losses that one can expect; (ii) the amount of leaching water that may result fromirrigating the plants; and (iii) potential food chain contamination when Atriplex grownon blowdown is consumed by wildlife or livestock. When Atriplex is grown onagricultural drain water as a forage crop the productivity and forage quality of thebiomass are important considerations. Data to answer these questions have beenjudged to be sketchy (Karajeh et al., 1994) or were obtained under unnaturalconditions, such as pot experiments (Miyamoto et al., 1996); thus the followingexperiments were conducted to generate realistic data.

Materials and methods

Lysimeter experiments were conducted from October 1993 to October 1996 atArizona Public Services, Inc., Ocotillo Electric Generating Station in Tempe, AZ. Thesite is a former cotton farm on a terrace of the nearby Salt River; preliminaryexcavation of the site soil with a backhoe showed it to be a deep alluvial sandy loam(Typic Torrefluvent) with no clear stratification to a depth of 1·5 m. The experimentalsite contained 32 buried gravity drain lysimeters (1·23 m diameter, 1·36 m deep).Water drained to a central sump and was collected in buckets. Experiments with A.nummularia were conducted in a block of eight adjacent lysimeters with 4 m betweencenters; the lysimeters were made of cylindrical, cardboard forms of the type used toform concrete columns (Border Products, Phoenix, AZ) fitted with a 0·05 cmthickness, inside PVC liner. The liner had watertight tank fitting at the bottom throughwhich a thin-walled (0·2 cm) PVC drainage pipe passed. The drain pipe was perforatednear the bottom of the lysimeter with slots to allow drain water to exit and was coveredby a layer of geotextile membrane. Lysimeters were placed in holes excavated with apower-driven, 1·5-m diameter auger. The soil from each excavation was refilled intothe lysimeter with a top clearance of 5 cm and was flood-irrigated.

E. GLENN ET AL.46

Irrigation treatments

Each of the eight lysimeters was assigned to one of two treatments, thus providing fourreplicates. Pond water was obtained from a collection pond on site, which containedprimarily storm runoff from the site, but which also received overflows of cooling towerblowdown water. Blowdown water was water from the cooling towers that was rejectedafter 7–10 cycles. Water quality analyses at the start of the experiment are shown inTable 1. Each water source was stored in 8000 l capacity, closed tanks from whichwater was withdrawn for irrigation. Tanks were refilled as needed. The salinity of waterin the tanks was measured approximately every other week during the main irrigationseason (March–September) when the tank contents changed rapidly, and lessfrequently in winter. The mean salinity of pond water by electrical conductivity was1149 mg l–1 (SE = 76, N = 37) while the blowdown water was 4100 mg l–1 (SE = 155,N = 45) over the study.

Each lysimeter was irrigated with either blowdown or pond water throughout thestudy. Four lysimeters were assigned to each water source in a staggered design,alternating pond or blowdown waters between adjacent lysimeters. The field capacityof the lysimeter soil was determined at the start of the experiment by measuringvolumetric soil moisture at 30 cm 24 h after an irrigation; values ranged from 25–27%among lysimeters. Volumetric soil moisture content was measured once a week fromMarch–September and every second or third week during the remainder of the year, atfour soil depths (30, 60, 90 and 120 cm) using a neutron hydroprobe (CampbellPacific Nuclear). The amount of water needed to restore the lysimeter to field capacitywas calculated, and, if it represented less than 75% of field capacity, the lysimeter wasirrigated with a volume of water calculated to bring the soil back to field capacity. Thewater was flooded uniformly over the surface of the lysimeter in one or twoapplications; irrigation volumes ranged from 40–250 l (4–25 cm) per application. Soilmoisture content was measured 24 h after irrigation to confirm that lysimeters wererestored to field capacity. During the first and second years, Peter’s Complete SoilTest Fertilizer (20-20-20, N-P-K) was added to irrigation water at a rate of 0·1 g l–1.However, nitrate levels were > 5 mol m–3 in 1:1 soil extracts by the end of the secondyear, and fertilizer was not added in the third year. The salinity and volume, if any, ofleachate water was checked before irrigating the lysimeters, and the buckets wereemptied. Hence, any leachate encountered represented drainage over the previous

Table 1. Analyses of Ocotillo power plant pond and blowdown water at the start ofthe lysimeter experiments in Tempe, AZ

Pond Blowdown

pH 7·24 6·96TDS (mg l–1) 1725 5732Na (mg l–1) 310 1074K (mg l–1) 8·08 30·8Mg (mg l–1) 41·8 173Ca (mg l–1) 76·2 246Cl (mg l–1) 390 1300NO3 (mg l–1) 1·57 23·5PO4 (mg l–1) <0·5 3·2SO4 (mg l–1) 742 2780H2CO3 (mg l–1) 155 149Arsenic (mg l–1) <0·01 0·02

TDS: total dissolved solids=the sum of cations and anions.

WATER USE BY ATRIPLEX 47

irrigation cycle. Leachate buckets were also checked and emptied following asignificant rain. Weekly evapo-transpiration (ET) was calculated as irrigation volume– drainage volume. Changes in soil water storage between irrigations were notconsidered in the calculation because the lysimeters were returned to field capacityeach week; precipitation (discussed later) was small in relation to annual ET and wasnot included in the calculations. The accuracy of the ET estimates was determined bythe accuracy of the measurements of irrigation and drainage volumes made in the fieldusing calibrated 20 l containers (error < 5%).

Planting and plant sampling

Three crops were grown over 3 years in the sequence summarized in Table 2. Eachlysimeter was planted initially (October 1993) with three seedlings (c. 5 cm height,mean dry weight of tops = 0·7 g per plant, SE = 0·2, subsample of 10 seedlings) of A.nummularia obtained from a local nursery (Desert Trees, Tucson, AZ). The plantswere laid out in a staggered row spacing with 0·6 m between plants within and betweenrows; the row pattern was continued outside each lysimeter so that each had threeplants inside the basin and nine guard plants outside the basin, representing portionsof four rows with 0·6 m between plants. An outer plastic ring was placed around theguard plants so that they could be flood-irrigated as were the plants inside thelysimeters. At the end of the first season (September 1994), plants were thinned to oneplant per lysimeter by random selection of the two plants to be removed. Plants werecut at ground level, weighed, separated into stems and leaves, and dried to constantweight in a solar-drier (40–50°C) for determination of dry biomass production. Oneguard plant per basin was also randomly selected for harvest to compare with lysimeterplants, and the remaining plants were allowed to grow until the end of the secondseason (September 1995), when all plants inside and outside the lysimeters wereharvested. In December 1995, all basins were replanted with new seedlings from thesame nursery source; these were larger than the 1993 seedlings, plant height 10–20 cm(mean dry weight tops = 5·7 g per plant, SE = 0·6, subsample of 10 seedlings). Theywere allowed to grow to the third and final sampling (September 1996). One plant perlysimeter was randomly selected for determination of biomass yield, leaf area indexand nutritional quality. Hence, there were three crops; Crop 1 (October 1993–Sep-tember 1994) and Crop 3 (December 1995–September 1996) represented plants inthe establishment year whereas Crop 2 (October 1994–September 1994) representedplants that were partially harvested at the end of the first year and allowed to regrowfor a second harvest.

Annual biomass production was estimated as the total amount of new biomassproduced each year in each basin. For Crop 1, the biomass of the two plants harvested

Table 2. Planting sequence of Atriplex nummularia grown in lysimeters atTempe, AZ, 1993–1996. Growth period is the month/year of planting and harvest

Crop No. Growth period Description

1 10/93–9/94 Nursery seedlings, 5 cm tall, spacing 0·6 m (threeplants in lysimeters, nine guard plants around eachlysimeter)

2 10/94–9/95 Plants thinned to one per lysimeter (1·2 m spacingbetween lysimeter plant and surrounding guardplants), harvested after 1 year

3 12/95–9/96 Replant lysimeter and guard plants as for Crop 1, butseedlings 10–20 cm tall. Harvest after 10 months

E. GLENN ET AL.48

from each basin was multiplied by 1·5 to estimate total biomass production (the weightof the transplants was ignored in the calculation). For Crop 2, the starting weight ofthe remaining plant was estimated by assuming it was the same as the mean of the twoharvested plants, and this was subtracted from the biomass of the remaining plant atharvest one year later. For Crop 3, the single plant harvested per lysimeter wasmultiplied by three to estimate total biomass production. Annual yield was slightlydifferent than annual biomass production. Crop 1 yield was only two-thirds of totalbiomass production since one plant ways left to grow, while Crop 2 yield was the totalharvest rather than the harvest minus the initial plant weight; however, cumulativeCrop 1 + 2 yields are the same as cumulative biomass production.

Soil, water and plant analyses

Soil samples were taken from each lysimeter at the start of the experiment (October1993), and after the first, second and third harvest (October 1994, 1995 and 1996,respectively). For the initial sampling, one sample per lysimeter was taken at 30 cmdepth, since the soil had been mixed and not yet irrigated. For subsequent samplings,three core samples per lysimeter were taken at 30, 60 and 90 cm depth and combinedby depth for analysis. Samples were placed in sealed plastic bags and kept underrefrigeration until analysis, generally within 48 h of sample collection. Soil, water andplant tissues were analysed by the Soil, Water and Plant Analysis Laboratory,Department of Soil, Water and Environmental Science, University of Arizona(Tucson) using EPA-certified methods; common cations were determined by ICP andanions by ion chromatography. Arsenic was determined by graphite furnace.Bicarbonate was by titration. Soil analyses were conducted on 1:1 soil:water (w/w)extracts. Soil bulk density was determined by removing top soil to a depth of 15 cm,inserting a thin-walled metal cylinder (489 cm3) into the soil, excavating the soil in thecylinder, and drying at 105°C. Soil levels in the lysimeters did not change appreciablyduring the experiment, hence bulk density was assumed to be constant as well. Salinityof irrigation and leachate water was measured in the field with an electricalconductivity meter (Myron L Company) calibrated with a 5 mg l–1 solution of NaCl.Leachate samples were diluted with distilled H2O to contain c. 1–5 mg l–1 TDS priorto making the final measurement.

Proximate analyses of dry stem and leaf samples were conducted by LaboratoryConsultants, Inc., Tempe, AZ. Eight priority metal pollutants in plant tissues weremeasured by ICP methods (EPA 6010A) except mercury which was by EPA 7471A atMcKenzie Laboratories, Phoenix, AZ. Metals and minimum detection limits inmg kg–1 are: arsenic (5·0), barium (2·5), cadmium (2·5), chromium (2·5), lead (5·0),mercury (0·3), selenium (5·0) and silver (2·5). Plant leaf area index (LAI) wascalculated by selecting 10 fully-expanded leaves per plant for measurement of one-sided surface area and dry weight; LAI for the whole plant was calculated from the dryweight of leaves per plant.

Meteorological data

Maximum and minimum daily temperatures were measured at 2 m height and panevaporation (Epan) was measured using a Class A pan on a wooden pallet. Additionalmeteorological data and computation of reference crop evapo-transpiration (ETo) bymodified Penman equation were from an AZMET station (Department of Soil, Waterand Environmental Science, University of Arizona) in Scottsdale, approximately10 km from the experimental site (Brown, 1996). Potential evapo-transpiration wasalso calculated from mean monthly temperature (AZMET data) and percent daytime

WATER USE BY ATRIPLEX 49

hours using the Blaney-Criddle formula (ECbc) (American Society of Civil Engineers,1973) as required by the Arizona Department of Environmental Quality in theirdefinition of best management practices for water reuse. AZMET data werecontinuously collected whereas site data were collected weekly during the mainirrigation seasons but with breaks in data collection during winter.

Calibration of neutron hydroprobe

Soil samples were taken for gravimetric moisture determination adjacent to probeports in soil ranging in moisture content from dry to saturated and a linear regressionequation was calculated to relate gravimetric moisture content to count ratios (%H2O = 21·5 3 count ratio, SE = 2·9, N = 27) (Hanson & Dickey, 1993). Gravimetricmoisture content was converted to volumetric moisture by multiplying by the bulkdensity of the soil, 1·45 g cm–3 (SE = 0·02, N = 5).

Statistical analyses

Yearly treatment means of plant growth and water consumption were analysed by two-way ANOVA for a completely randomized design in which year and water source werecategorical variables; soil parameters were analysed by three-way ANOVA in whichyear, water source and sample depth were categorical variables. Equations relating ETto meteorological data were developed using linear regression analyses. Statistical andregression analyses were computed using CoStat software.

Results

Overall development of plants in the experimental block

Plant heights increased each month during the establishment year but reached amaximum height of 160–180 cm during the second year of growth (Fig. 1). During thesecond year most new growth appeared to be from secondary branches instead of the

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E. GLENN ET AL.50

main plant axis, and plant height actually decreased during the winter, as many of themain stems collapsed due to the weight of their side branches. During Crop 1 thelysimeter and guard plants formed a closed canopy around each lysimeter by April. BySeptember the guard and lysimeter plants had grown to form a closed block (128 m2)encompassing all eight lysimeters, which was kept in place throughout Crop 2 exceptfor narrow paths kept open to reach each lysimeter. Crop 3 transplants formed a closedcanopy around each lysimeter by March. Lysimeter plants and guard plants wereallowed to intergrow throughout the study, and there was no significant difference(p > 0·05) between lysimeter and guard plants in fresh weights at harvest through thestudy; hence, it was accepted that the measurements made on lysimeter plants wererepresentative of results that would be obtained from a closed-canopy stand of A.nummularia during the establishment year and second year of growth after partialharvesting.

Meteorological conditions, Epan and Eo

Tempe has a hot desert climate. Mean monthly temperatures ranged from 11 to 37°Cover the study, following the same annual pattern at both the experimental andAZMET sites, but averaging approximately 1°C warmer at the experimental site (Fig.2(a)). The experimental site was surrounded by bare soil whereas the AZMET site wassurrounded by grass. Rainfall was 21·5 cm, 19·9 cm and 10·0 cm for the three cropyears, respectively, occurring as occasional winter or late summer rain storms. Annualprecipitation was 3–10% of the amount applied as irrigation water but contributedsignificantly to leachate production as will be shown later. Eo, calculated fromAZMET wind, radiation, temperature and humidity data for a reference crop, was65% of Epan measured at the site, which is the expected ratio (American Society ofCivil Engineers, 1973). Eo and Epan were similar in winter and diverged the most insummer (Fig. 2(b)). Ebc, which is calculated from mean monthly temperature 3 dailyphotoperiod, closely followed the seasonal temperature curves in Fig. 2(a). Over the 3study years, mean Eo was 201 cm year–1, Ebc was 182 cm year–1, while Epan was309 cm year–1.

Water use, leaching fraction and biomass production

Irrigation demand (Fig. 3(a)) followed the same pattern as the seasonal temperatureand evaporation data. However, the peak irrigation demand (50–90 cm in July)exceeded peak Epan each year. There was little apparent difference in ET betweenblowdown or pond treatments. Very little leachate was produced from the lysimeters(Fig. 3(b)) compared to the irrigation volume applied, and production was irregular,occurring mainly after significant rain events. The salinity of the leachate tended toincrease over the study, reaching 45,000 mg l–1 in the blowdown and 20,000 mg l–1 inthe pond treatments (Fig. 3(c)).

Annual values for biomass production, ET and WUE are shown in Table 3, whileannual leachate volume and salinity are in Table 4. Biomass production did not differsignificantly (p > 0·05) by crop or water source, and was very high, with a mean drymatter productivity of 4·4 kg m–2 year–1 over the study. ET was significantly (p < 0·05)lower for Crop 1 than for Crops 2 and 3, perhaps due to the smaller starting size of theplants that year, but there was no difference (p > 0·05) between pond or blowdownwater. Mean ET over the study was 285 cm year–1; 157% of Ebc, 142% of Eo and 92%of Epan. WUE did not differ by year or water source and was high, with a mean of1·6 kg m–3. Leachate production tended to be sporadic with large standard errorsamong lysimeters (Table 4). There was no significant difference in leachate volume by

WATER USE BY ATRIPLEX 51

year or water source. Mean leachate volume over the study was 20 cm year–1,approximately the same as the mean annual rainfall (17 cm year–1). LF wassignificantly higher (p < 0·05) in the first year than in subsequent years. The mean LFover the study was 0·074. Lysimeters irrigated with blowdown water had significantly(p < 0·05) higher salt concentration in the leachate water than lysimeters irrigated withpond water. Annual salt production was higher from lysimeters irrigated withblowdown rather than pond water and tended to increase over time; however due tothe high standard errors the differences were not significant (p > 0·05). Neither pondnor blowdown lysimeters reached salt balance during the study. Over Crop 3, 3·4 kgsalt was applied to pond lysimeters while 2·1 kg emerged in leachate; 11·1 kg wasapplied to blowdown lysimeters while only 3·6 kg emerged.

Soil moisture and soil salinity

Soil moisture levels preceding irrigation followed the same pattern for each crop andare illustrated for plants in the second year of growth over summer, when rootpenetration and water demand were maximal (Fig. 4). Soil moisture was depletedmost near the soil surface but water content was below field capacity (25% volumetric)

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E. GLENN ET AL.52

at all depths, indicating that water was extracted from throughout the soil profile withno difference between pond and blowdown treatments in extraction patterns. Plantsdid not appear to be water-limited during the study as mean moisture content was> 65% of field capacity even during the period of maximum water demand.

EC, Na and Cl in soil samples taken from different depths in the lysimeters areshown in Table 5. All three measures of soil salinity increased with increasing soildepth (p < 0·05) and were higher in lysimeters irrigated with blowdown rather thanpond water (p < 0·05), but they did not increase significantly by year (p > 0·05). Thedata from 1:1 extracts can be converted to salinity of the soil solution by dividing NaClper g soil by the gravimetric moisture content. Based on soil moisture contentsmeasured before an irrigation (see Fig. 4) and results in Table 5, the NaCl content inthe soil solution at 30–90 cm depth ranged from 40–90 mol m–3 (2300–5200 mg l–1)and 300–1000 mol m–3 (17,400–58,000 mg l–1) in lysimeters irrigated with pond andblowdown water, respectively, during the peak summer growing season. The meansalinity of the soil solution exceeded seawater (540 mol m–3 NaCl) in the blowdownlysimeters.

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Figure 3. (a) Mean monthly irrigation demand, (b) leachate production and (c) leachate salinityof A. nummularia irrigated with pond (s) or blowdown (d) water at the Ocotillo power plant,Tempe, AZ.

WATER USE BY ATRIPLEX 53

Predicting ET from atmospheric water demand

In Arizona, permission to use industrial waste water on crops requires following bestmanagement practices which specify that irrigation volume cannot exceed crop waterdemand. Irrigation scheduling must be based on monthly crop coefficients relating ETto Ebc. ET data for pond and blowdown treatments were combined for furtheranalyses. ET was generally < 10 cm month–1 from October through February but roserapidly after March (Fig. 5(a)); the ratio of ET to Eo followed the same seasonal trend;< 1 from October through February but increasing to 2–3 by July (Fig. 5(b)).Correlation coefficients relating monthly ET to estimates of E over all crops were: Eo,r = 0·71***; Epan, r = 0·76***; and Ebc, r = 0·85***. Thus the best correlation was withECbc. The linear equation of best fit was: ET (cm month–1) = 4·04 Ebc–37·3(r2 = 0·72***).

We attempted to improve the prediction by considering each crop separately and byincluding a measurement of crop development as an additional predictive factor.Especially during the early stage of crop growth when LAI is increasing, ET should bea function of Ebc 3 LAI. We did not measure LAI over each crop, as this would bedifficult in routine irrigation scheduling, so we substituted plant height data(interpolated from Fig. 1). Monthly ET over Crops 1, 2 and 3 was regressed againstEbc and Ebc 3 plant height and equations of best fit were calculated (Table 6). ForCrop 1, which started with very small transplants and had lower ET than Crops 2 and

Table 3. Means and standard errors of annual water use (l m–2), biomass yield(kg dry wt. m–2) and water use efficiency (WUE, g dry wt. l–1) of

Atriplex nummularia irrigated with pond or blowdown water for 3 years atTempe, AZ. Significant differences (<0·05) among years are indicated by different

letters after the year. The significance levels (NS, *, **, or ***) of the maintreatment effects and their interactions are in the two-way ANOVA results at the

bottom of the table

Pond water Blowdown waterMean SE Mean SE

Water use Yr 1a 2002 155 2250 86Yr 2b 3167 212 3364 67Yr 3b 3483 158 2771 161

Mean 2884 2795

Yield Yr 1 3·75 1·12 4·09 0·78Yr 2 4·13 0·97 4·90 0·57Yr 3 4·91 0·54 4·60 0·56

Mean 4·26 4·53

WUE Yr 1 1·76 0·23 1·82 0·40Yr 2 1·31 0·27 1·46 0·16Yr 3 1·40 0·11 1·66 0·17

Mean 1·49 1·65

ANOVA results: Watertype (W) Year (Y) W×Y

Water use NS *** NSYield NS NS NSWUE NS NS NS

E. GLENN ET AL.54

Table 4. Means and standard errors of leachate volume (l ), leachate salinity(mg l–1), leaching fraction (LF) and leachate salt content (g per basin) of

Atriplex nummularia irrigated with pond or blowdown water for 3 years atTempe, AZ. Significant differences (<0·05) between pond water or blowdown watertreatments are indicated by different letter after means; significant differences among

years are indicated by different letters after the year. The significance levels(NS,*,**,***) of the main treatment effects and their interactions are in the two-

way ANOVA results at the bottom of the table

Pond water Blowdown waterMean SE Mean SE

Leachate volume Yr 1 351 111 250 30Yr 2 210 99 114 45Yr 3 169 54 109 42

Mean 243 162

Leachate salinity Yr 1a 3082 280 3157 171Yr 2b 12,811a 7758 35,666b 5280Yr 3b 15,625a 4534 39,201b 6463

Mean 10,506a 24,808b

LF Yr 1a 0·165 0·055 0·101 0·029Yr 2b 0·060 0·026 0·032 0·012Yr 3b 0·050 0·013 0·039 0·015

Mean 0·091 0·057

Leachate salt Yr 1 1166 463 910 156content Yr 2 1264 373 3815 1517

Yr 3 2165 493 3605 1160

Mean 1532 2776

ANOVA results: Watertype (W) Year (Y) W×Y

Leachate volume NS NS NSLeachate salinity ** *** *LF NS ** NSLeachate salt content NS NS NS

3, the best predictor of ET was Ebc 3 plant height. By contrast, Crops 2 and 3 werebest predicted by Ebc alone. Combining data for Crops 2 and 3 gave a simple linearequation that can be used to accurately predict ET for plants of 20 cm height or above:ET (cm month–1) = 4·64 Ebc–43·1.

Quality of harvested biomass

Leaves and stems harvested from Crop 3 were analysed in detail (Table 7). Plants wereapproximately 40% leaves and 60% stems and the percentage was not significantly(p < 0·05) affected by irrigation treatment. (Plants from Crop 2 had approximately thesame ratio of stems to leaves but stems were thicker). Tissue moisture and ash contentswere significantly (p < 0·05) higher in plants irrigated with blowdown than pond water.Mean leaf area index was 2·6 and did not differ significantly (p > 0·05) by water source.Proximate analyses were conducted on pooled samples so statistical comparisonsbetween pond and blowdown treatments are not possible; however, plants irrigated

WATER USE BY ATRIPLEX 55

with blowdown water tended to have higher protein content than plants irrigated withpond water, despite higher ash content. Aggregating the results for stems and leaves,A. nummularia had 10·4% crude protein, 21·2% crude fiber, 1·7% crude fat, 46·3%digestible matter and 15·1% ash. The only priority metal pollutant detected in theplant tissues was barium, present at 5–13 mg kg–1. Arsenic, cadmium, chromium, lead,mercury, selenium and silver were below detection limits of the assays employed.

Discussion

Atriplex nummularia exhibited many characteristics desired in a plant to be used forrecycling brine water. The mean annual ET of 285 cm compares favorably withEucalyptus trees planted to intercept brine, which used 115 cm over 220 days in theSan Joaquin valley (Karajeh & Tanji, 1994a,b). High ET minimizes the amount ofland that must be devoted to recycling brine. Irrigation demand could be accuratelyestimated from the Blaney-Criddle formula for potential evaporation, which onlyrequires mean monthly temperature data and hours of daylight. The coefficient

1.5

25

Depth (m)

% M

oist

ure

0.5

5

20

15

10

10

(a)

1.5

25

Depth (m)

% M

oist

ure

0.5

5

20

15

10

10

(b)

Figure 4. Volumetric soil moisture content (%) at different soil depths in A. nummularialysimeters measured just before a scheduled irrigation with (a) pond or (b) blowdown water atthe Ocotillo Power Plant, Tempe, AZ. Data points are the mean of weekly measurements takenduring Crop 2, June–August 1994. Bars are SE.

E. GLENN ET AL.56

relating annual ET to Epan, 0·92, was higher than the coefficient of 0·65 for high-ETreference crops such as alfalfa or grass (American Society of Civil Engineers, 1973;Allen et al., 1992), and the ratio Eo/ET increased during the growing season. This mayhave been partly due to the increase in LAI as each crop developed; however, regrowthof Crop 2 from already established plants followed the same general pattern of Eo/ETas Crops 1 and 3, indicating that stomatal conductance was probably lower in winterthan in summer thereby reducing ET, a characteristic of those Atriplex spp. which growmainly during the hot season (Osmond et al., 1980). The results are also similar tothose reported for established stands of the hydrophytes, cattail and bulrush (Allen etal., 1992), for which the ratio Eo/ET varied from 0·4 to 1·8 between winter andsummer, respectively. Even though A. nummularia is a desert-adapted species, the

Table 5. Means and standard errors (beneath means) of soil electrical conductivity(EC, dS m–1 in 1:1 extract), Na (µg g–1) and Cl (µg g–1) at three sample depths inlysimeter basins in which Atriplex nummularia was grown on pond or blowdownwater for 3 years at Tempe, AZ. Within a water type, means at different sample

depths are significantly different at p<0·05 if followed by a different letter.The significance levels (NS, *, **, ***) of the main treatment effects and their

interactions are in the three-way ANOVA results at the bottom of the table

Pond water Blowdown water

30 cm 60 cm 90 cm 30 cm 60 cm 90 cm

EC Yr 1 0·548a 0·594a 1·23b 2·45a 4·74b 7·42c

0·070 0·073 0·36 0·51 0·21 0·41Yr 2 0·514a 0·567a 1·28b 3·01a 5·80b 8·40c

0·053 0·038 0·61 1·19 1·59 1·61Yr 3 0·552a 0·458a 0·658a 2·35a 5·61b 8·93c

0·062 0·085 0·20 0·93 2·22 2·49

Mean 0·538 0·540 1·056 2·60 5·38 8·25

Na Yr 1 96·5a 103·5a 176b 372a 538b 1084c

14·9 11·1 51 51 69 201Yr 2 67·8a 77·8a 205b 375a 1182b 1721c

4·9 2·9 122 106 418 393Yr 3 98·4ab 89·5a 133b 480a 1000b 2108c

9·4 10·5 42 196 319 436

Mean 87·6 90·3 171 409 907 1638

Cl Yr 1 66·3a 67·8a 125b 276a 517b 1188c

16·3 10·9 35 35 67 223Yr 2 50·5a 66·3a 172b 352a 906b 1396c

8·1 4·8 89 158 361 458Yr 3 70·0 67·5 72·5 317a 385a 1488b

11·6 15·7 12·7 77 89 789

Mean 62·3 67·2 123 315 603 1357

ANOVA results: Water Sampletype (W) depth (D) Year (Y) W×D W×Y W×D×Y

EC *** *** NS *** NS NSNa *** *** NS *** NS NSCl *** *** NS ** NS NS

WATER USE BY ATRIPLEX 57

Sep

3.5

0

Oct

ET

/Eo

Apr

1

3

2.5

2

1.5

0.5

Nov

Jan

Feb

Mar

May

Jun

Jul

Au

g

80E

T (

cm m

onth

–1)

30

70

60

50

40

20

10

0

(b)

(a)

Dec

Figure 5. Monthly values of (a) evapo-transpiration and (b) the ratio of evapo-transpiration topotential evaporation from a reference crop for A. nummularia Crop 1 (s), 2 (d) and 3 (n) atthe Ocotillo power plant, Tempe, AZ. Results for pond and blowdown water are combined.

Table 6. Coefficients of determination (r2) and equations of best fit relatingAtriplex nummularia ET (cm month–1) to Ebc (cm month–1) and plant height

(ht, cm) at Tempe, AZ. The equation is for the case that gave the higher r2

r2

Crop ET (Y) Ebc (X1) Ebc×ht (X2) Equation

1 0·56** 0·82*** Y=0·0179 (X2)+0·0583

2 0·96*** 0·74*** Y=3·76 (X1)–30·6

3 0·87*** 0·58*** Y=5·52 (X1)–56·2

2+3 0·87*** 0·41*** Y=4·64 (X1)–43·1

E. GLENN ET AL.58

present results show that when soil moisture is not limiting it is capable of very rapidgrowth and ET, and plant performance is not affected by high levels of soil salinity.

The leaching fraction is controlled to a large extent by soil permeability andirrigation management. When high frequency irrigation of saline water is employedjust to replace the previous soil water depletion, the ability of plants to extract waterfrom saline solutions becomes the controlling factor. The LF of A. nummularia on theblowdown treatment, 0·06, was much lower than the typical value of 0·25 forEucalyptus (Karajeh et al., 1994), resulting in more efficient utilization of brine water.A low LF reduces the volume of water that must be recovered via subsurface drains ordischarged to the aquifer. When salt-tolerant conventional crops such as cotton weregrown on agricultural brine, the brine could only make up 50% of ET, and the rest hadto be supplied by rainfall and supplemental, low-salinity water in order to controlsalinity in the root zone (Ayars et al., 1993). By contrast, A. nummularia was able totolerate seawater salinity in the soil solution with no reduction in ET. Rainfall aloneprovided sufficient leaching to keep salt content in the top 90 cm at reasonably stablelevels, even though rainfall in Tempe was only 17 cm year–1. The rainfall-inducedleaching can be reduced by using deficit irrigation during the rainy season, but it maynot be a significant factor in soils with large water-holding capacity.

Salinity of the drainage water collected increased with years and reached as high as45,000 mg l–1. These observations are consistent with our earlier analyses that it willtake several years to attain the apparent steady state with respect to soil salinity at lowLF (Miyamoto, 1996). At the average LF of 0·036 during the third year, the salinityof the leachate could increase even more. However, our earlier experiments haveshown that the salinity at which A. nummularia can extract water may not exceed80,000 mg l–1, which is higher than most other plants. What is even more significant isthe fact that A. nummularia extracted water from such high salinity solutions evenwhen the soil surface layer has received relatively low salinity water. According to thetheory of osmotic adjustment, the plant could have extracted water only from the

Table 7. Water and ash contents of stems and leaves (g g–1 dry wt.), nutritionalquality and leaf area index of Atriplex nummularia plants grown on pond water or

blowdown water in Tempe, AZ (Crop 3). Standard errors of means are inparentheses. Means followed by different letters in a row are significantly different atp<0·05. The significance levels (NS,*,**,***) of one-way ANOVAs with watertype as the treatment effect are also given. Nutritional analyses were conducted on

pooled samples

Pond Blowdown ANOVA

Stem H2O 0·843 (0·030)a 0·982 (0·016)b **Leaf H2O 1·411 (0·119)a 1·773 (0·079)b *Stem ash 0·093 (0·012) 0·104 (0·006) NSLeaf ash 0·212 (0·016)a 0·255 (0·010)b *Leaf area index 2·36 (0·46) 2·87 (0·62) NSStem protein 7·80 8·82Leaf protein 12·90 15·15Stem crude fat 0·79 0·62Leaf crude fat 1·81 2·51Stem crude fiber 30·73 31·78Leaf crude fiber 6·05 6·05% Digestible stem 47·26 49·27% Digestible leaf 39·74 46·61Stem barium (mg kg–1) 13 3·6Leaf barium 7·4 5·3

WATER USE BY ATRIPLEX 59

surface layer where soil salinity was low, thus leaving soil solutions below poorlyconcentrated. The fact that A. nummularia has concentrated the soil solutions to thisextent under frequent and non-deficit irrigation seems to confirm that this plant canindeed offer a means to concentrate ordinary saline water in a cropped soil bed.

Annual biomass production (4·4 kg m–2) and WUE (1·6 kg m–3) were nearly twice ashigh as conventional forage crops such as alfalfa grown in the same county (Wade et al.,1994) (Fig. 6). Atriplex nummularia is a C4 plant with expected high WUE (Osmondet al., 1980). The present yields were 4–5 times higher than yields obtained for Atriplexin the San Joaquin Valley (Watson, 1990; Watson & O’Leary, 1993). Those plantingswere irrigated at widely spaced intervals whereas ours were under high frequency andnon-deficit irrigation.

Atriplex nummularia had high protein and digestible matter content, low fiber and amoderate ash content (Table 7), within the range of values of conventional foragesources (National Academy of Sciences, 1971). Although protein content wassomewhat lower than alfalfa (10 vs. 13%) and mineral content was higher (15 vs.10%), A. nummularia yielded much more protein and organic matter than alfalfa perunit area due to its high biomass yield. Accumulation of salt is part of the adaptationprocess of halophytes to salinity (Glenn et al., 1994), hence mineral levels were higherin plants grown on blowdown water. Earlier feeding trials, however, have shown thatAtriplex and other halophyte biomass containing up to 30% mineral content canreplace conventional forages at 30% inclusion in fattening rations for ruminants withno decrease in weight gain or carcass quality (Swingle et al., 1996). Hence, A.nummularia can potentially produce an economic return when grown on brine underhigh frequency and non-deficit irrigation, even though Atriplex crops are not widelyproduced or utilized by the animal feed industry.

The build-up of boron and selenium in plant tissues can limit the use of brine waterfor irrigation in some locations (Ayars et al., 1993). Neither element was present atlevels of concern in the water supplies used here, and the only priority pollutantdetected in the plant tissues was barium which is ubiquitous in the soils at this site butdid not reach levels of concern. Arsenic was present at 20 µg l–1 in the blowdown waterat the start of the experiment and occasionally reached levels of concern for dischargeinto the municipal sewer system (EPA drinking water standard = 100 µg l–1) but it didnot reach a level of concern in considering the use of the plant tissue as a feedingredient. In the San Joaquin valley, A. nummularia irrigated with seleniforous drain

Figure 6. Mean annual ET and dry biomass production of Crops 1–3 (1993–1996) of A.nummularia grown on pond (s) or blowdown (d) water at the Ocotillo power plant, Tempe,AZ. Comparative values for sudan grass and alfalfa are for crops grown in Maricopa county,AZ.

E. GLENN ET AL.60

water for 27 months contained 0·6 mg kg–1 selenium and 189 mg kg–1 boron, belowNRC maximum recommended levels for ruminants assuming that Atriplex wouldmake up 30% of the animal diet (Watson et al., 1994; National Research Council,1980). Hence, forage produced on drain water appears to be safe to use as a feedingredient. However, the duration of the experiments were too short to evaluate thetrace element effect that might result from slow accumulation of elements in thesoil.

References

Allen, R., Prueger, J. & Hill, R. (1992). Evapotranspiration from isolated stands of hydrophytes:cattail and bulrush. Transactions of the ASAE, 35: 1191–1198.

American Society of Civil Engineers (1973). Consumptive Use of Water and Irrigation WaterRequirements. New York: American Society of Civil Engineers. 215 pp.

Ayars, J., Hutmacher, R., Schoneman, R., Vail, S. & Pflaum, T. (1993). Long term use of salinewater for irrigation. Irrigation Science, 14: 27–34.

Brown, P. (1996). AZMET evapotranspiration estimates: a tool for improving water management ofturfgrass. Arizona Meteorological Network Bulletin. Tucson, AZ: University of ArizonaCollege of Agriculture, Cooperative Extension Service. 6 pp.

Engel, R., Malzer, G. & Bergsrud, F. (1985a). Saline cooling tower water for irrigation inMinnesota: I. Crop and soil effects. Journal of Environmental Quality, 14: 32–36.

Engel, R., Malzer, G. & Bergsrud, F. (1985b). Saline cooling tower water for irrigation inMinnesota: II. Drainage water composition, leaching fraction, and effect on aquifer quality.Journal of Environmental Quality, 14: 36–40.

Glenn, E., Miyamoto, S., Moore, D., Brown, J.J., Thompson, T.L. & Brown, P. (1997). Waterrequirements for cultivating Salicornia bigelovii Torr. with seawater on sand in a coastal desertenvironment. Journal of Arid Environments, 36: 711–730.

Glenn, E., Olsen, M., Frye, R., Moore, D. & Miyamoto, S. (1994). How much sodiumaccumulation is necessary for salt tolerance in subspecies of the halophyte Atriplex canescens?Plant, Cell and Environment,17: 711–719.

Hanson, B. & Dickey, G. (1993). Field practices affect neutron moisture meter accuracy.California Agriculture, 47: 29–31.

Karajeh, J. & Tanji, K. (1994a). Agroforestry drainage management model. II: Field water flow.Journal of Irrigation and Drainage Engineering, 120: 382–396.

Karajeh, F. & Tanji, K. (1994b). Agroforestry drainage management model. III: Field salt flow.Journal of Irrigation and Drainage Engineering, 120: 397–413.

Karajeh, F., Tanji, K. & King, I. (1994). Agroforestry drainage management model. I: Theoryand validation. Journal of Irrigation and Drainage Engineering, 120: 363–381.

Miyamoto, S. (1996). Salt tolerance, water use and potential irrigation scheduling of halophytes.In: Choukr-Allah, R., Malcolm, C. & Hamdy, A. (Eds), Halophytes and Biosaline Agriculture,pp. 181–220. New York: Marcel-Dekker. 400 pp.

Miyamoto, S. & Mueller, W. (1994). Irrigation with saline water: certain environmentalconsiderations. Proceedings of the International Symposium on Salt Affected Soils, pp. 231.Acapulco, Mexico: International Soil Science Congress. 231 pp.

Miyamoto, S., Glenn, E.P. & Olsen, M. (1996). Growth, water use and salt uptake of fourhalophytes irrigated with highly saline water. Journal of Arid Environments, 32: 141–159.

National Academy of Sciences (1971). Atlas of Nutritional Data on United States and CanadianFeeds. Washington, D.C.: National Academy of Sciences. 772 pp.

National Research Council (1980). Mineral Tolerance of Domestric Animals. Washington, D.C.:National Academy of Sciences. 577 pp.

Ong, C. & Tanji, K. (1993). Evaporative concentration of trace elements in a multicellagricultural evaporation pond. Journal of Agricultural and Food Chemistry, 41: 1507–1510.

Ong, C., Tanji, K., Dahlgren, R., Smith, G. & Quek, A. (1995). Water quality and traceelement evapoconcentration in evaporation ponds for agricultural waste water disposal.Journal of Agricultural and Food Chemistry, 43: 1941–1947.

Osmond, C.B., Bjorkman, O. & Anderson, D.J. (1980). Physiological Processes in Plant Ecology.New York: Springer-Verlag. 468 pp.

WATER USE BY ATRIPLEX 61

Presser, T. (1994). The Kesterton effect. Environmental Management, 18: 437–454.Rhoades, J., Bingham, F., Letey, J., Hoffman, G., Dedrick, A., Pinter, P., Alves, W., Swain, R.,

Pacheco, P., Lemert, R. & Replogle, J. (1989). Use of saline drainage water for irrigation:imperial valley study. Agricultural Water Management, 16: 25–36.

Riley, J., Fitzsimmons, K. & Glenn, E. (1997). Halophyte irrigation: an overlooked strategy formanagement of membrane filtration concentrate. Desalination, 110: 197–211.

Swingle, R., Glenn, E. & Squires, V. (1996). Growth performance of lambs fed mixed dietscontaining halophyte ingradients. Animal Feed Science & Technology, 63: 137–148.

Wade, J., Daugherty, L. & Husman, S. (1994). 1994–1995 Arizona Field Crop Budgets. Tucson,Arizona: University of Arizona, Department of Agricultural and Resource Economics.48 pp.

Watson, M. (1990). Atriplex species as irrigated forage crops. Agriculture, Ecosystems andEnvironment, 32: 107–118.

Watson, M. & O’Leary, J. (1993). Performance of Atriplex species in the San Joaquin Valley,California, under irrigation and with mechanical harvests. Agriculture, Ecosystems andEnvironment, 43: 255–266.

Watson, M., Banuelos, G., O’Leary, J. & Riley, J. (1994). Trace element composition of Atriplexgrown with saline drainage water. Agriculture, Ecosystems & Environment, 48: 157–162.

Westcott, D. (1988). Reuse and disposal of higher salinity subsurface drainage water — a review.Agricultural Water Management, 14: 483–511.

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