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Agricultural Water Management 97 (2010) 1277–1286

Contents lists available at ScienceDirect

Agricultural Water Management

journa l homepage: www.e lsev ier .com/ locate /agwat

ptimizing the rate and timing of phosphogypsum application toagnesium-affected soils for crop yield and water

roductivity enhancement

. Vyshpolskya, K. Mukhamedjanova, U. Bekbaeva, S. Ibatullina, T. Yuldashevb, A.D. Noblec,. Mirzabaevb, A. Aw-Hassand, M. Qadird,e,∗

Water Conservation Laboratory, Kazakh Research Institute of Water Management, 12 Koygeldy Street, Taraz, KazakhstanInternational Center for Agricultural Research in the Dry Areas (ICARDA), Central Asia and Caucasus Regional Office, Osiyo 6, Tashkent, UzbekistanInternational Water Management Institute (IWMI), South East Asia Office, P.O. Box 4199, Vientiane, Lao People’s Democratic RepublicICARDA, P.O. Box 5466, Aleppo, SyriaIWMI, P.O. Box 2075, Colombo, Sri Lanka

r t i c l e i n f o

rticle history:eceived 13 December 2009ccepted 28 February 2010vailable online 3 April 2010

eywords:agnesium to calcium ratio

xchangeable magnesium percentagealt-affected soilshosphogypsumater quality

entral Asiaazakhstanotton

a b s t r a c t

The levels of magnesium (Mg2+) in irrigation waters and soils are increasing in several irrigation schemesworldwide. Excess levels of Mg2+ in irrigation waters and/or in soils negatively affect soil physical prop-erties (infiltration rate and hydraulic conductivity) and ultimately crop growth and yield. Although fewstudies have been undertaken on productivity enhancement of magnesium-affected soils by adding asource of calcium (Ca2+) to mitigate the effects of excess Mg2+, there is no information available onoptimizing the rate and time of the Ca2+-amendments. A 2-year field study was undertaken in southernKazakhstan by applying phosphogypsum (PG), a source of Ca2+ and a byproduct of the phosphorous fertil-izer industry, to a magnesium-affected soil. There were five treatments with four replications: (1) control(without PG application); (2) PG application in January (before snowfall) equivalent to PG requirementfor 0.3 m soil depth (3.3 t ha−1); (3) PG application in January equivalent to PG requirement for 0.6 m soildepth (8.0 t ha−1); (4) PG application in April (after snowmelt) at 3.3 t ha−1; and (5) PG application in April(after snowmelt) at 8.0 t ha−1. All treatment plots were grown with cotton (Gossypium hirsutum L.), whichis the most important summer crop in the region. The PG treatments performed significantly better thanthe control in terms of (1) improved soil quality with a reduction in exchangeable magnesium percentage(EMP) levels; (2) enhanced water movement into and through the soil vis-à-vis increased moisture stor-

age in the root zone for use by the plant roots; (3) increased irrigation efficiency; (4) increased cotton yieldand water productivity; and (5) greater financial benefits. In terms of the best rate and time of application,PG applied before the snowfall improved the soil properties to a greater extent than its application inspring after snowmelt. The economic benefits from the amendment application at 3.3 t ha−1 were doublethose from the treatments where it was applied at 8.0 t ha−1, suggesting that the lower rate was econom-ically optimal. In addition to improving crop productivity, the study demonstrated the beneficial use of

rial in

an industrial waste mate

. Introduction

Recent evidences from several irrigation schemes worldwide

eveal increasing levels of magnesium (Mg2+) in irrigation watersnd irrigated soils than those found in previous decades. Thesemerging trends can be found in parts of the Aral Sea Basin inentral Asia, the Cauca River Valley in Colombia, and the Mur-

∗ Corresponding author at: ICARDA, P.O. Box 5466, Aleppo, Syria.el.: +963 21 26912535/2213433; fax: +963 21 2213490.

E-mail address: m.qadir@cgiar.org (M. Qadir).

378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.agwat.2010.02.020

agriculture.© 2010 Elsevier B.V. All rights reserved.

ray Darling Basin in Australia (Garcia-Ocampo, 2003; Qadir andDe Pauw, 2007; Vyshpolsky et al., 2008). High-Mg2+ irrigationwaters are characterized by Mg2+ levels higher than calcium (Ca2+),suggesting Mg2+:Ca2+ ratio greater than 1 (Qadir and De Pauw,2007). Magnesium-affected soils contain exchangeable magnesiumpercentage (EMP) in the range of 25–45% (Abbott, 1987; Garcia-Ocampo, 2003), and in some cases, as high as 60% (Bekbaev et al.,

2005).

Excess levels of Mg2+ in irrigation waters and/or in soils incombination with sodium (Na+) or alone result in soil degra-dation through impacts on soil physical properties (Oster andJayawardane, 1998; Qadir and Schubert, 2002; Zhang and Norton,

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278 F. Vyshpolsky et al. / Agricultural W

002; Karimov et al., 2009). The major reason for the specificg2+ effect is that the hydration energy and hydration radius ofg2+ are greater than Ca2+ (Bohn et al., 1985). Thus, the soil sur-

ace tends to absorb more water than where exchangeable Ca2+ isresent, resulting in weakening of the forces that keep soil particlesogether. This, in turn, decreases the amount of energy required toreak down soil aggregates (Oster and Jayawardane, 1998). At low

evels of exchangeable Na+, Mg2+ also enhances the effects of Na+

n clay dispersion and hydraulic conductivity (Rengasamy et al.,986; Qadir and Schubert, 2002). In addition, high-Mg2+ levels inoils tend to increase surface sealing and erosion (Dontsova andorton, 2002).

More than 30% of the irrigated area in southern Kazakhstan isepresented by magnesium-affected soils (Bekbaev et al., 2005).

ith low infiltration rates and hydraulic conductivities, these soilsorm large dense clods during the drying post-irrigation phase,hich impact the water flow rate. The consequence of using high-g2+ soils and waters for agricultural production systems without

uitable management practices has been a gradual decline in cot-on (Gossypium hirsutum L.) yield in the region (Vyshpolsky et al.,008; Karimov et al., 2009).

The productivity of magnesium-affected soils can be enhancedy increasing Ca2+ on cation exchange sites to mitigate the effectsf excessive exchangeable Mg2+ (Vyshpolsky et al., 2008). This cane accomplished by applying sufficient amounts of Ca2+ to the soilGhafoor et al., 1992; Karajeh et al., 2004), an amelioration strat-gy similar to sodic soils (Oster, 1982; Qadir and Oster, 2004).hosphogypsum, the main byproduct in the production of phos-hate fertilizer from phosphate rock, is a source of Ca2+ as it isainly composed of gypsum (CaSO4·2H2O). Phosphogypsum does

ontain variable amounts of some impurities such as naturally-ccurring radionuclides, fluoride, and heavy metals depending onource (Rutherford et al., 1994; Abril et al., 2009; Villa et al., 2009).owever, short- and long-term studies (years to decades) have

hown that its use in agriculture as a soil amendment does notroduce significant increases in the concentrations of these con-tituents in soils (Al-Oudat et al., 1998; El-Mrabet et al., 2003; Abrilt al., 2008). Rather, phosphogypsum application to agriculturaloils could contribute to diluting the radionuclide wastes comparedo phosphogypsum stacks outside the phosphate fertilizer industryosing a major environmental hazard. Soil application of phosph-gypsum has additional value to farmers (El-Mrabet et al., 2003;yshpolsky et al., 2008). In addition to increasing soil Ca2+ levels,hosphogypsum supplies appreciable quantities of phosphorous tohe soil (Alcordo and Rechcigl, 1993; Delgado et al., 2002).

Although the beneficial effects of phosphogypsum applicationn enhancing the productivity of magnesium-affected soils haveeen demonstrated in the region (Vyshpolsky et al., 2008), there

s no information available on the appropriate combinations of theate and timing of applications to mitigate high-Mg2+ levels in soils.

ith the participation of a local farming community, a 2-year fieldtudy on a magnesium-affected soil in southern Kazakhstan wasndertaken to determine the effects of different rates and timingf phosphogypsum application on: (1) changes in the soil chemi-al properties; particularly salinity and magnesium levels; (2) soiloisture retention and irrigation efficiency; (3) growth, yield, andater productivity of cotton; and (4) economics of the applied

reatments.

. Materials and methods

.1. Study area and site characterization

In collaboration with the local farming community, this on-farmtudy was undertaken during the years 2005–2007 in southern

anagement 97 (2010) 1277–1286

Kazakhstan. Cotton is the main crop grown in the region cover-ing about 95% of the cropped area in summer. The selected site wasin the Old Ikan area within the command zone of Arys TurkestanCanal. Site characterization was undertaken in September 2005.The Old Ikan area has a smooth landscape with slopes from 0.002 to0.0035. Long-term annual precipitation ranges from 50 to 250 mm,with 90% occurring during October through May. The average pre-cipitation during the study period (May–September) was 18 mm.The area has high summer temperatures (30–40 ◦C) during June,July and August. The temperature declines to as low as −10 ◦C, withan average of 2 ◦C, during the winter months. The soils are heavyloam with about 1% organic matter in the surface layer and cationexchange capacity (CEC) in the range of 10.8 and 12.6 cmolc kg−1.Soil bulk density is 1.56±0.05 Mg m−3 and pH varies narrowly from8.1 to 8.2. The EMP levels in soil usually vary in the range of 30% and40%, while exchangeable sodium percentage (ESP) levels remainbelow 3%.

2.2. Treatments

The following five treatments were established in a completelyrandomized block design with four replications with a plot size of1000 m2.

1 Control (without phosphogypsum, PG, application).2 Soil application of PG in January 2006 (before snowfall) equiv-

alent to PG requirement for 0.3 m soil depth (3.3 t ha−1); laterreferred to as PG3.3–Jan.

3 Soil application of PG in January 2006 (before snowfall) equiv-alent to PG requirement for 0.6 m soil depth (8.0 t ha−1); laterreferred to as PG8.0–Jan.

4 Soil application of PG in April 2006 (after snow melt) equivalentto PG requirement for 0.3 m soil depth (3.3 t ha−1); later referredto as PG3.3–Apr.

5 Soil application of PG in April 2006 (after snow melt) equivalentto PG requirement for 0.6 m depth (8.0 t ha−1); later referred toas PG8.0–Apr.

The rate of phosphogypsum application (phosphogypsumrequirement, later referred to as PGR) to the soil was calculatedfrom the quantity of gypsum requirement as given in Eq. (1).

PGR = GR0.8

(1)

where PGR referred to the quantity of PG required (t ha−1), GR wasquantity of gypsum required (t ha−1), and 0.8 the conversion fac-tor between phosphogypsum and gypsum. In order to determinegypsum requirement of the soil for input to Eq. (1), Eq. (2) was used.

GR = 0.086 (EMg − 0.3CEC) (100ds) �b (2)

where EMg was exchangeable Mg2+ level in soil (cmolc kg−1), CECreferred to cation exchange capacity of the soil (cmolc kg−1), ds thedepth of soil amelioration (m), and �b the bulk density of the soil(Mg m−3).

The amendment was applied to the respective treatments onceat the beginning of the study either in January (PG3.3–Jan andPG8.0–Jan) or in April (PG3.3–Apr and PG8.0–Apr). No phosphogypsumwas applied to experimental plots in the subsequent years.

2.3. Soil and water sampling and analysis

After laying out the experiment plots, soil samples were col-lected from three randomly selected points in each experimentalplot at the following depths: 0–0.15, 0.15–0.30, 0.30–0.60, and0.60–0.90 m. Composite soil samples for each plot were preparedafter mixing three sub-samples for each soil depth. Soil sampling

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F. Vyshpolsky et al. / Agricultural W

as undertaken before the implementation of the treatments (ini-ial soil condition) and after harvest of cotton in each cropping year.he collected samples were air-dried and processed for the follow-ng parameters: pH by colorimetric method; electrical conductivityEC) by electrical conductivity meter; soluble cations including Ca2+

nd Mg2+ by titration with ethylenediaminetetracetate (EDTA), anda+ and potassium (K+) by flame photometry; and soluble anions

ncluding carbonate (CO32−) and bicarbonate (HCO3

−) by titrationith sulfuric acid, chloride (Cl−) by titration with silver nitrate,

nd sulfate (SO42−) by precipitation as barium sulfate (U.S. Salinity

aboratory Staff, 1954). Sodium adsorption ratio (SAR) was calcu-ated using Eq. (3) from the concentrations (C) of soluble cationsa2+, Mg2+, and Na+, expressed as mmolc L−1.

AR = CNa

[(CCa + CMg)/2]1/2(3)

The soil samples were further analyzed for exchangeable cationsncluding magnesium (EMg), calcium (ECa), and sodium (ENa). Cationxchange capacity (CEC) was calculated as the sum of the exchange-ble cations (ECa + EMg + ENa). Exchangeable magnesium percentageEMP) was calculated using Eq. (4) where EMg and CEC werexpressed as cmolc kg−1.

MP = 100(EMg)CEC

(4)

The measured soil physical attributes consisted of particle-sizenalysis, field capacity, infiltration rate, saturated hydraulic con-uctivity, bulk density, and moisture content. Particle-size analysisas assessed using one randomly selected sample from 0 to 0.15,

.15 to 0.30, 0.30 to 0.60, and 0.60 to 0.90 m depths in each treat-ent by sedimentation method using sodium hexametaphosphate

s a dispersing agent. Field capacity was determined from a ran-omly selected location (2 m × 2 m) in each treatment by flooding,overing of flooded area with polyethylene sheet, and determiningoil moisture in the following days up to the time (usually 3–5 days)hen there was minimal change in moisture content at all the soilepths. Infiltration rate and saturated hydraulic conductivity wereetermined using standard double ring metallic infiltrometers withn outer ring diameter of 0.4 m and inner ring diameter of 0.3 m.oth rings were buried in the soil to a depth of 0.10–0.15 m. Soilulk density was determined on undisturbed soil samples collectedrom each soil depth using the core method. Soil moisture contentas determined by gravimetric method.

In order to determine water quality, irrigation and groundwateramples were collected on monthly basis. These samples were ana-yzed for the following parameters: pH, EC, soluble cations (Ca2+,

g2+, Na+, and K+) and anions (CO32−, HCO3

−, Cl−, and SO42−). In

ddition to groundwater quality, groundwater level was monitoredach month during the crop growth season (May–September).roundwater level ranged from 1.04 to 2.56 m during the 2006otton growth season and from 1.24 to 2.45 m during the 2007eason.

.4. Field operations

The field was plowed with a tractor during the first weekf January 2006. This was followed by soil application of PG tohe respective treatments at the rate of 3.3 t ha−1 (PG3.3–Jan) and.0 t ha−1 (PG8.0–Jan). The amendment was applied to other PG treat-ents in the first week of April 2006 (PG3.3–Apr and PG8.0–Apr).s a part of the seedbed preparation, furrows were made in the

lots on 22 April 2006. In order to facilitate the leaching of salts,articularly Mg2+ replaced from the cation exchange sites, a pre-owing irrigation of 800 m3 ha−1 was undertaken on 2 May 2006.arrowing with a tractor was performed just before cotton sowing.otton variety C-4727 was sown in all the plots with a cotton seeder

anagement 97 (2010) 1277–1286 1279

(Model: SPC-3.6) on 9 May 2006. The cultural practices for cottoncultivation in the control and PG plots were the same and in accor-dance with the prevalent system of agriculture used in the region(Umbetaev and Batkaev, 2000). Nitrogen in the form of ammoniumnitrate (NH4NO3) was applied at the rate of 130 kg ha−1 on 9 June2006. Nitrogen as bio-fertilizer (bio-nitrogen) was applied at therate of 3 L ha−1 in late July 2006. Cotton was harvested in September2006 and yield from each plot was recorded. In the subsequent year(2007), all the agronomic and fertilizer management practices werethe same except that a greater volume of water (1400 m3 ha−1) wasused for pre-sowing irrigation and leaching of Mg2+ removed fromthe cation exchange sites.

2.5. Irrigation management and water productivity evaluation

Arys Turkestan canal water was used for irrigation. To estimateirrigation water entering the experimental site, the trapezoidalIvanov’s weirs [Model: SANIIRI weirs (WS) with the side slope of1:1] were installed. In order to monitor irrigation water appli-cation to each treatment, the triangle Thomson’s weirs [Model:WT-50 with angle 90◦] were installed in the main irrigation fur-rows, which were 0.15 m deep and 0.30 m wide. The soil moisturecontent was monitored using the Diviner 2000 instrument throughplastic access tubes installed to a depth of 1.5 m. The sensor technol-ogy of the Diviner 2000 utilizes Frequency Domain Reflectometry(FDR) to measure soil moisture to a depth of 1.5 m at 0.1 m intervals.In order to calibrate the soil moisture measurements estimated byDiviner 2000 and gravimetric soil moisture content method, soilsampling was undertaken from the same horizons (soil depths) ineach treatment. Soil samples were collected in tin cans and soilmass was determined before and after oven-drying. The soil mois-ture content for a specific soil depth (�d) on dry weight basis wascalculated using Eq. (5) (Gardner et al., 2001).

�d = wet mass − dry massdry mass

(5)

Subsequently, �d was converted into soil moisture content onvolume basis (�) expressed as m3 m−3 by considering the bulk den-sity (�b) of the respective soil layer (Eq. (6)).

� = �d × �b (6)

Total soil moisture within a specified soil depth was calculatedas a product of � and soil depth (expressed in terms of mm). Totalsoil moisture for the 0.9 m soil profile was estimated by addingvalues of total soil moisture at the four specified soil depths, i.e.0–0.15, 0.15–0.30, 0.30–0.60, and 0.60–0.90 m.

Available soil moisture within a specified soil depth was esti-mated as the difference between total soil moisture in that soildepth and soil moisture at permanent wilting point (PWP). Soilmoisture at PWP was considered as half of soil moisture at fieldcapacity as there was lack of facilities to determine soil moistureat PWP. This relationship is close to the estimated values of soilmoisture at field capacity and at PWP in the area of field study.Available soil moisture for the 0.9 m soil profile was estimated byadding values of available soil moisture at the four specified soildepths (0–0.15, 0.15–0.30, 0.30–0.60, and 0.60–0.90 m).

Irrigation efficiency (IE) in the different treatments was calcu-lated in terms of percentage using Eq. (7) where NIR referred to netirrigation rate (m3 ha−1) and GIR represented gross irrigation rate(m3 ha−1).

IE = NIRGIR

100 (7)

In order to estimate NIR, the differences in soil moisture con-tent (before and after irrigation application) at four depths (0–0.15,0.15–0.30, 0.30–0.60, and 0.60–0.90 m) were determined. The sum

1280 F. Vyshpolsky et al. / Agricultural Water Management 97 (2010) 1277–1286

Table 1Physical properties of the field site within the command zone of Arys Turkestan Canal in southern Kazakhstan before start of the experiment in October 2005.

Soil characteristic Unit Soil depth (m)

0.0–0.15 0.15–0.30 0.30–0.60 0.60–0.90

Sand (0.05–2.0 mm diameter) % 23.78 21.44 20.53 19.23Silt (0.002–0.05 mm diameter) % 53.41 54.27 55.31 59.40Clay (<0.002 mm diameter) % 22.81 24.29 24.16 21.37Soil texture (USDA classification) – Silt loam Silt loam Silt loam Silt loamGravimetric field capacity % 23.1 22.2 21.3 21.2Volumetric field capacity m3 m−3 0.353 0.349 0.349 0.348

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f the differences in soil moisture content was considered as NIR.urface runoff (SR, m3 ha−1) was measured after starting irrigationn hourly basis in the tail of the furrow using triangle Thom-on weirs. Percolation losses (PL, m3 ha−1) were calculated as:L = GIR − (NIR + SR). Water productivity (WP, kg m−3) in differentreatments was calculated using Eq. (8) where Y represented yieldf cotton (kg ha−1) and W the water applied (m3 ha−1) to the fieldgross irrigation + rainfall).

P = Y

W(8)

.6. Economics of applied treatments

The total cost of production for the different treatments wasalculated by differentiating cost components such as cultiva-ion, which included plowing, furrow making, harrowing, chiseling,ottonseed, sowing operations, weeding and cleaning of field, har-esting, and transportation of the harvested material. Other costsor the treatments consisted of fertilizer purchase and application,rrigation management, labor charges, and farm machinery. Theost of phosphogypsum application in the respective treatmentsas reported for the first year of the experiment in 2006 becauseo amendment was applied in subsequent years. This cost includedransportation and field application of the amendment. There waso cost for amendment application in the control. The values ofll costs computed in Kazakh Tenge were converted into US dollarUS$), considering the currency exchange rate for the respectiveear.

In order to evaluate the economics of different treatments,arginal rates of returns (MRR) were calculated. The MRR is the

atio between the change in net benefit and the change in totalost and reveals the returns to the additional investment due toechnology adoption. The data on the economic evaluation werenalyzed using Microsoft Office Excel. MMR was calculated usingq. (9):

RR = 100NBi − NBo

TCi − TCo(9)

here MRR is the marginal rate of return (%), NBi the net benefit ofhosphogypsum applied in respective treatments (US$ ha−1), NBo

et benefit of the control treatment (US$ ha−1), TCi the total costor respective phosphogypsum treatments (US$ ha−1), and TCo theotal cost for the control treatment (US$ ha−1).

. Results and discussion

.1. Pre-experiment soil physical and chemical characteristics

According to the classification system of the United Statesepartment of Agriculture (USDA) for particle-size distribution,

he soil was silt loam in texture throughout the profile to a depth

– – –1.57 1.64 1.640.337 0.344 0.34550.6 103.1 103.5

of 0.90 m (Table 1). Field capacity in the upper 0.15 m soil depthwas 23.1%; for the 0.15–0.30 m depth, its value was 22.2%. At the0.30–0.60 m and 0.60–0.90 m depths, the values of field capacitywere measured to be 21.3% and 21.2%, respectively. Infiltrationrate of the pre-experiment soil was relatively low (16.5 mm h−1),this being a consequence of the high levels of Mg2+ on the cationexchange complex in the upper soil depth (EMP 36%). High lev-els of exchangeable Mg2+ are similar to those soils dominated byhigh levels of Na+, i.e. sodic soils that are easily dispersed whenwet (Sumner, 1993; Qadir and Schubert, 2002). Soil bulk den-sity increased with depth and ranged from 1.53 to 1.64 Mg m−3

(Table 1).The pre-experiment soil salinity levels, expressed in terms of

soil electrical conductivity (ECe) at different soil depths extend-ing up to 0.9 m were in the range of 1.44–1.61 dS m−1 with thehighest value observed in the upper 0.15 m (Table 2). Among theanions, HCO3

2− was dominant with a maximum concentration of9.47 mmolc L−1 in the upper 0.15 m depth, which decreased withincreasing soil depth; the lowest values (6.80 mmolc L−1) were atthe 0.6–0.9 m depth. Varying in the range of 4.53 to 5.67 mmolc L−1,the overall concentrations of SO4

2− were less than that of HCO32−

and had a slightly increasing trend from surface to deeper soil lay-ers; the highest levels found at 0.6–0.9 m depth. The concentrationsof Cl− were much less than that of SO4

2− and ranged from 1.73to 2.13 mmolc L−1 at different soils depths. The determination ofCO3

2− did not result in detectable concentrations when soil sam-ples from different depths were analyzed.

Among the soluble cations in the pre-experiment soil, Mg2+

concentrations were higher at the soil surface than other majorcations, Na+ and Ca2+ (Table 2). The concentration of Mg2+ inthe upper 0.15 m depth was 6.00 mmolc L−1. It also followed apattern similar to the dominant anion (HCO3

2−) as its concentra-tion had a decreasing trend with depth and varied from 4.67 to6.00 mmolc L−1. Sodium concentrations did not differ substantially(5.07–5.80 mmolc L−1) at different soil depths. Calcium concentra-tions ranged from 4.0 to 5.0 mmolc L−1. The soil has an alkaline pH,ranging from 8.03 to 8.15. The SAR levels had a slight increasingtrend with depth and ranged from 2.19 to 2.79. Exchangeable mag-nesium percentage ranged from 36.08 to 43.88. It increased withthe depth, with the highest levels in the 0.6–0.9 m depth. Similarlyexchangeable Mg2+, increased with increasing soil depth. Contrast-ing this exchangeable Ca2+ levels decreased with increasing soildepth. It would appear that magnesium-induced problems in thesesoils are not confined to the surface soil, but occurred throughoutthe 0.9 m soil depth.

3.2. Irrigation and groundwater quality

Salt concentration in irrigation water, expressed as EC, rangedfrom 0.64 to 0.72 dS m−1 during the 2006 crop growing season(Table 3). In addition to the low levels of salts (<1 dS m−1), there

F. Vyshpolsky et al. / Agricultural Water Management 97 (2010) 1277–1286 1281

Table 2Average values of various soil chemical parameters of the field site in southern Kazakhstan before implementation of the treatments in October 2005.

Soil characteristic Unit Soil depth (m)

0.0–0.15 0.15–0.30 0.30–0.60 0.60–0.90

pH – 8.13 8.15 8.03 8.10Soil salinity (ECe) dS m−1 1.61 1.50 1.45 1.44Soluble Ca2+ mmolc L−1 5.00 5.00 4.00 4.00Soluble Mg2+ mmolc L−1 6.00 5.00 4.67 4.67Soluble Na+ mmolc L−1 5.13 5.07 5.73 5.80Soluble HCO3

2− mmolc L−1 9.47 7.73 7.07 6.80Soluble Cl− mmolc L−1 2.13 1.87 1.73 2.00Soluble SO4

2− mmolc L−1 4.53 5.47 5.60 5.67Exchangeable Ca2+ cmolc kg−1 7.33 7.40 7.30 6.53Exchangeable Mg2+ cmolc kg−1 4.20 4.43 4.53 5.20Exchangeable Na+ cmolc kg−1 0.11 0.13 0.13 0.12

−1

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CEC cmolc kg 11.64SAR – 2.19EMP – 36.08

as limited variation in terms of salt concentration in irrigationater. Similar trends were observed in terms of salt concentra-

ion and variability (0.69–0.73 dS m−1) during the 2007 cottoneason. In addition to relatively low levels of salinity, sodicityevels in irrigation water (0.45–1.10) remained low throughouthe 2006 and 2007 cotton seasons. Based on the water qual-ty guidelines regarding the combined effects of EC and SAR onnfiltration problems in soils (Ayers and Westcot, 1985), thesealues suggest no restriction on use for irrigation. The pH of irri-ation water was alkaline and ranged, with little variation, from.30 to 8.75 in 2006 and from 8.25 to 8.70 in 2007. The dom-

nant cation was Mg2+ with concentrations ranging from 2.7 to.5 mmolc L−1 in 2006 and from 2.50 to 3.10 mmolc L−1 in 2007. Theominant anion in irrigation water samples collected during theotton season in 2006 was HCO3

2− with small temporal variationsn its concentrations, which varied from 3.36 to 3.69 mmolc L−1

n 2006. In 2007, the HCO32− concentrations varied from 2.10 to

.00 mmolc L−1 (Table 3). The concentrations of SO42− were less

han that of HCO32− and ranged from 0.29 to 2.82 mmolc L−1 at

ifferent sampling times during both years. Similarly, Cl− con-entrations varied from 0.56 to 2.36 mmolc L−1. No detectableoncentrations of CO3

2− were found in irrigation water samplesollected over the 2 years.

The major limiting factor with respect to quality of irrigationater used at the experimental site was Mg2+:Ca2+ ratio, which was

onsistently greater than 1, sometimes approaching 2 (Table 3). Theritical value of Mg2+:Ca2+ ratio in irrigation water is considereds 1, above which there are implications for soil degradation with

ong-term irrigation (Ayers and Westcot, 1985; Vyshpolsky et al.,008). Although limited research and data are available on evaluat-

ng the effects of different Mg2+:Ca2+ ratios in irrigation water, theyeveal enhanced deleterious effects on soil quality and crop yield

able 3hemical composition of irrigation water used to grow cotton at the experimental site ov

Characteristic Unit 2006

May July

pH – 8.75 8.30EC dS m−1 0.64 0.72Ca2+ mmolc L−1 1.76 2.65Mg2+ mmolc L−1 3.50 2.70Na+ mmolc L−1 1.10 1.80HCO3

2− mmolc L−1 3.36 3.55Cl− mmolc L−1 0.56 0.74SO4

2− mmolc L−1 2.44 2.82Mg2+:Ca2+ – 1.99 1.02SAR – 0.68 1.10

11.96 11.96 11.852.27 2.75 2.79

37.04 37.88 43.88

with an increase in Mg2+:Ca2+ ratio >1 (Ayers and Westcot, 1985;Ghafoor et al., 1992; Zhang and Norton, 2002). These water qualityattributes are commonly found in southern Kazakhstan (Karajeh etal., 2004). Long-term irrigation with high-Mg2+ has implications forimpaired soil structure leading to low hydraulic conductivity andinfiltration rate (Ayers and Westcot, 1985).

The salinity levels in groundwater ranged between 2.39 and2.90 dS m−1 in the 2006 growing season, and from 2.55 to3.11 dS m−1 in the 2007 season (Table 4). The salt concentration ingroundwater was 4–5 times greater than that of irrigation water.The groundwater pH was alkaline in reaction and higher than thatof irrigation water used at the experimental site. It ranged from 8.69to 9.34 in both years. The dominant cations were Na+ and Mg2+ withNa+ concentrations ranging from 16.20 to 20.05 mmolc L−1 in the2006 crop season and remained consistent in the following year(16.18–22.91 mmolc L−1). The Ca2+ concentration was almost halfof the Mg2+ concentration. The major anions in groundwater sam-ples were found to be SO4

2− (8.90–15.98 mmolc L−1) and HCO32−

(7.66–12.55 mmolc L−1). The levels of SAR were greater than that ofirrigation water; more than 10 at the beginning of the crop season,but progressively decreasing to around 8 by the end of the season. Itis argued that part of low-SAR irrigation water reaching groundwa-ter contributed to a decrease in SAR levels by the end of crop season.The ratio between the ionic concentrations of Mg2+ and Ca2+ wasmore than 2, approaching 4.69 in groundwater samples collectedduring May 2007. Salts of Mg2+ and Na+ mainly consisted of sodiumsulfate (Na2SO4), magnesium bicarbonate (MgHCO3), magnesiumsulfate (MgSO4), and sodium chloride (NaCl). The amounts of Ca2+

salts as calcium sulfate (CaSO4) were much less than the amountsof Mg2+ and Na+ salts. These results support the earlier findings ofthe studies conducted in the Arys Turkestan area (Vyshpolsky et al.,2008; Karimov et al., 2009).

er two consecutive years.

2007

August May July September

8.50 8.70 8.30 8.250.68 0.69 0.71 0.732.30 1.80 2.55 2.003.45 2.50 3.10 2.601.10 1.80 1.50 1.863.69 3.20 2.10 4.000.54 2.20 2.25 2.362.62 0.29 2.81 0.341.50 1.39 1.22 1.300.65 0.45 0.89 0.45

1282 F. Vyshpolsky et al. / Agricultural Water Management 97 (2010) 1277–1286

Table 4Chemical composition of groundwater at the experimental site over two consecutive years.

Characteristic Unit 2006 2007

May July August May July September

pH – 9.14 9.06 8.69 9.34 9.04 9.03EC dS m−1 2.90 2.75 2.39 3.11 2.65 2.55Ca2+ mmolc L−1 2.55 2.62 2.59 1.44 2.86 3.10Mg2+ mmolc L−1 6.40 6.39 5.15 6.76 6.32 6.26Na+ mmolc L−1 20.05 18.53 16.20 22.91 17.35 16.18CO3

2− mmolc L−1 1.50 1.57 Absent 4.21 1.43 1.30HCO3

2− mmolc L−1 8.00 8.19 12.55 7.66 8.11 8.04Cl− mmolc L−1 3.52 4.02 2.41 3.42 3.57 3.11

2− −1

3

hwfiwwobenttclEdtwdio2

3

(c

Foce

the years. However, there was no additional effect of the snowmelt

SO4 mmolc L 15.98 13.76Mg2+:Ca2+ – 2.51 2.44SAR – 10.87 9.67

.3. Soil electrical conductivity (EC)

Salinity determinations made on soil samples collected afterarvest of cotton in both the years reveal small increases in ECith respective to pre-experiment levels (Fig. 1). However, thenal EC levels in post-cotton 2007 samples from all the soil depthsere <2 dS m−1; a value half of the critical EC level (4 dS m−1),hich separates saline and non-saline soils (Soil Science Society

f America, 2009). In terms of changes in soil salinity as affectedy phosphogypsum application, there were no significant differ-nces among the phosphogypsum treatments. However, there waso clear trend for the increase in soil EC, which was probably dueo two reasons: (1) spatial variability in terms of salt distribu-ion in the soil profile, and (2) dissolution of phosphogypsum thataused small increase in soil salinity (up to 0.4 dS m−1), particu-arly in the upper 0.15 m soil depth where average pre-experimentC was 1.6 dS m−1, and HCO3

2− and Mg2+ were respectively theominant anionic and cationic species. Although solute concentra-ion did increase in the phosphogypsum-treated soils, this increaseas small in the treatments where the amendment was applied atifferent rates. Previous studies have also shown small increases

n soil salinity levels after soil application of gypsum or phosph-gypsum (Shainberg and Letey, 1984; Sumner, 1993; Qadir et al.,001).

.4. Exchangeable magnesium percentage (EMP)

Data from soil samples collected from different soil depths0–0.15, 0.15–0.30, and 0.30–0.60 m) after harvesting of the firstotton crop in 2006 indicated an overall decrease in EMP lev-

ig. 1. Salinity levels expressed as ECe (dS m−1) in the upper 0.60 m soil layer (meanf three soil depths; 0–0.15, 0.15–0.30, and 0.30–0.60 m) as affected by the appli-ation of phosphogypsum to the soil at different rates. Error bars indicate standardrror of the mean.

8.90 15.82 13.42 13.092.00 4.69 2.21 2.028.34 12.03 8.67 7.84

els in all the treatments where phosphogypsum was appliedat different rates and times. In terms of the cumulative effectof the treatments on the 0.60 m soil layer (mean of three soildepths; 0–0.15, 0.15–0.30, and 0.30–0.60 m), the treatments withphosphogypsum application resulted in a significant decreaseEMP levels (Fig. 2). However, there was no statistical differenceamong the phosphogypsum treatments where the amendmentwas applied either before the snowfall in January or after snow-fall in April, just before the cotton growing season. A similarpattern was observed when EMP levels were determined in thepost-cotton 2007 soil samples collected from different depths. Ingeneral, the impact of the phosphogypsum treatments on decreas-ing EMP levels was reduced at the lower soil depths (data notpresented).

The non-significant differences among the phosphogypsumtreatments can be explained in part by the fact that the amendmentwas applied once to the respective treatments at the beginning ofthe experiment. The snowmelt and precipitation in March and Aprilcontributed to the dissolution of phosphogypsum to release Ca2+

in the soil solution. In addition, cotton pre-sowing irrigation andleaching contributed to the movement of part of the amendmentto lower soil depths. The increased concentration of Ca2+ in thesoil solution triggered the replacement of Mg2+ from the cationexchange sites. This is evident from the data presented in Fig. 2on EMP levels in the soil profile after the harvest of cotton in both

in the treatments where the amendment was applied before thesnowfall events. This may be due to soil being frozen during snow-fall events and subsequent snowmelt could not effectively increasethe phosphogypsum dissolution.

Fig. 2. Exchangeable magnesium percentage (EMP) in the upper 0.60 m soil layer(mean of three soil depths; 0–0.15, 0.15–0.30, and 0.30–0.60 m) as affected by theapplication of phosphogypsum to the soil at different rates. Error bars indicatestandard error of the mean.

F. Vyshpolsky et al. / Agricultural Water M

Fig. 3. Average values of total soil moisture and available soil moisture in the 0.9 ms1ms

3

ddTau(bmttptpdatpshA

astotctw

wtt1Tp1wtt

quent year (2007), the cotton yield trend was in the order:PG3.3–Jan (2200 kg ha−1) > PG8.0–Jan (2100 kg ha−1) > PG3.3–Apr(2067 kg ha−1) > PG8.0–Apr (1900 kg ha−1) > control (1267 kg ha−1).

Based on the crop yield and water applied (gross irriga-tion + rainfall) data in the 2006 crop season, phosphogypsum

oil profile (determined at various time intervals; eight measurements in 2006 and0 measurements in 2007) and irrigation efficiency (%) as affected by different treat-ents during the cotton growing seasons (May–September). Error bars indicate

tandard error of the mean for each parameter.

.5. Available soil moisture and irrigation efficiency

The soil moisture content (soil moisture storage at the specifiedepth) in pre-experiment soil was 51.2 mm in the upper 0.15 m soilepth with limited variation over the 0.15–0.30 m depth (50.6 mm).he moisture content was 103.1 and 103.5 mm at the 0.30–0.60 mnd 0.60–0.90 m soil depths, respectively (Table 1). The greater val-es of soil moisture at the 0.30–0.60 m and 0.60–0.90 m soil depthsalmost double than the 0–0.15 m and 0.15–0.30 m depths) wereecause of greater soil depths (double than the upper depths). Soiloisture content was less than that calculated at field capacity. In

erms of cumulative response of the treatments to available mois-ure content during both the cropping seasons (May–September),hosphogypsum treatments retained significantly more moisturehan control (Fig. 3). The increase in soil moisture content in thehosphogypsum treatments is attributed to Ca2+ released from theissolution of the amendment, thereby improving soil structurend hydraulic properties (infiltration rate and hydraulic conduc-ivity) and enhancing water movement into and within the soilrofile. In addition, high water holding capacity of phosphogyp-um also contributed to water storage in the soil. Similar findingsave been reported by other researchers (Shainberg et al., 1989;lcordo and Rechcigl, 1993; Al-Oudat et al., 1998).

Among the phosphogypsum treatments, the treatment with themendment applied in January at the rate of 3.3 t ha−1 (PG3.3–Jan)tored significantly greater amount of available water (82.3 mm)han other phosphogypsum treatments (75.1–76.8 mm). In terms ofverall performance, the PG3.3–Jan and PG8.0–Jan treatments respec-ively had 25% and 17% more available moisture content than theontrol. The respective increase in available soil moisture in bothhe PG3.3–Apr and PG8.0–Apr treatments over the control treatmentas 14%.

The total amount of water applied in four irrigations during 2006as 3507 m3 ha−1. With a total irrigation volume of 3806 m3 ha−1,

he same number of irrigations was applied in 2007. In 2006, theotal amount of surface runoff under the control treatment was124 m3 ha−1, which was the maximum among for all treatments.his represents 32% of the gross irrigation rate. In the case of phos-

hogypsum treatments, the total amount of surface runoff was6–19% of the gross irrigation rate. The total amount of infiltrationas lowest (460 m3 ha−1) under control (13% of the gross irriga-

ion rate), while it ranged from 627 to 747 m3 ha−1 (18–21% ofhe gross irrigation rate) in the phosphogypsum treatments. The

anagement 97 (2010) 1277–1286 1283

lower amount of surface runoff and greater infiltration into thesoil under phosphogypsum treatments suggest the beneficial roleof the calcium-supplying amendment in improving soil structure,thereby storing more water in the root zone for plant growth (Al-Oudat et al., 1998; Shainberg et al., 1989). The treatments exhibiteda similar trend in the second year with respect to surface runoff andinfiltration into the soil.

Evaluation of the irrigation efficiency—estimated as the per-centage of the ratio of net irrigation rate and gross irrigationrate—revealed phosphogypsum treatments performing signifi-cantly higher than control (Fig. 3). Compared to the averageirrigation efficiency of the control treatment (52.2%), the corre-sponding values for the phosphogypsum treatments were in therange of 59.2 to 60.2%. These observations reveal that total avail-able soil moisture and irrigation efficiency were closely related andhad significantly greater values for the phosphogypsum treatmentsthan the control treatment.

3.6. Cotton growth and yield, and water productivity

Plant density in the phosphogypsum treatments (162,000 plantsha−1) was significantly higher in comparison with the control(139,000 plants ha−1) suggesting that seedling emergence wasenhanced through the beneficial effects of Ca2+ supplied throughthe amendment application. The plots with amendment applica-tion in January before snowfall had higher plant density than theamendment application in April. Similar trends were observed inthe phosphogypsum and control treatments in the number of bolls.Similar trends for plant density and number of bolls were found inthe subsequent year. Based on the number of bolls per unit area inthe phosphogypsum treatments, the anticipated cotton yields wereexpected to be more than 2 t ha−1. However, a hurricane with awind velocity of 20–25 m s−1 occurred at the beginning of Septem-ber 2006. Usual wind velocity in the region is around 2 m s−1. Theunexpected high velocity wind blew away cotton bolls with an esti-mated reduction in boll number to be 28–36%. This wind eventimpacted cotton yield, which was reduced by approximately 30%.

In 2006, the maximum cotton yield (2080 kg ha−1) was recordedin PG8.0–Jan treatment, followed by PG3.3–Jan (1867 kg ha−1),PG3.3–Apr (1690 kg ha−1), PG8.0–Apr (1633 kg ha−1) and con-trol (1300 kg ha−1) (Fig. 4). The typical cotton yield inthe region ranges between 1.0 to 1.4 t ha−1. In the subse-

Fig. 4. Cotton yield (kg ha−1) in 2006 and 2007 as affected by different treatments.Error bars indicate standard error of the mean.

1284 F. Vyshpolsky et al. / Agricultural Water M

Fa

ttobaifPIo(Tp

awi

($ 386). However, the increase in yield as a result of phosphogyp-

TM

s

d

ig. 5. Average values of water productivity (mean of 2006 and 2007; kg m−3) asffected by different treatments. Error bars indicate standard error of the mean.

reatments had statistically higher water productivity values thanhe control treatment in both the years. Among the phosph-gypsum treatments, the treatments receiving phosphogypsumefore snowfall in January performed better than those where themendment was applied in April. The maximum water productiv-ty (0.500 kg m−3) in 2006 was recorded in PG8.0–Jan treatment,ollowed by PG3.3–Jan (0.449 kg m−3), PG3.3–Apr (0.407 kg m−3),G8.0–Apr (0.393 kg m−3), and control treatment (0.313 kg m−3).n the subsequent year (2007), the water productivity was in therder: PG3.3–Jan (0.570 kg m−3) > PG8.0–Jan (0.545 kg m−3) > PG3.3–Apr0.536 kg m−3) > PG8.0–Apr (0.493 kg m−3) > control (0.328 kg m−3).he average values of water productivity for 2006 and 2007 areresented in Fig. 5.

Enhanced productivity of water in agricultural systemsddresses net benefits gained in various forms through the use ofater in crop, forestry, fishery, and livestock sectors, and their var-

ous combinations (Molden, 1997; Hussain et al., 2003; Molden et

able 5ajor economic indicators under different treatments (except for benefit cost ratio and m

Expenditure/income Control PG3.3–Jan

Year 2006Phosphogypsumb – 104Cultivationc 268 307Fertilizer purchase and application 23 23Water and irrigation 95 95Total cost 386 528Gross incomed 473 694Net income 87 166Benefit cost ratio 1.23 1.31Marginal rate of return (MRR) 55

Year 2007Cultivationc 364.3 374.3Fertilizer purchase and application 41.7 41.7Water and irrigation 62.4 62.4Total cost 468.4 478.4Gross incomed 700 1050Net income 232 572Benefit cost ratio 1.49 2.19Marginal rate of return (MRR) 42

a The expenditures and income determined in local currency (Kazakh Tenge) were conb Includes purchase, transportation, and field application costs of phosphogypsum du

ubsequent year.c Includes costs on plowing, making furrows, harrowing, chiseling, purchasing cotton

ifferences among treatments for cultivation costs were mainly due to harvesting and trad Derived from the product of cotton yield and market price of cotton in the region in t

anagement 97 (2010) 1277–1286

al., 2007). In the present study, water productivity values reflectedthe objectives of producing cotton per unit of water added to differ-ent treatments in the production process. Considering the trendsof increasing water scarcity in the foreseeable future, there is agreater need to use the available freshwater supplies more effi-ciently (Hatfield et al., 2001; Wichelns and Oster, 2006; Qadir etal., 2007) where producing more crop and having greater benefitswith the same amount of water used in the process, or produc-ing the same amount of crop and having similar benefits withthe less amount of water used in the process are crucial consid-erations. Comparative evaluation of water productivity of varioustreatments would help researchers and farmers in selecting waterefficient interventions.

The increase in cotton yield and water productivity in thephosphogypsum-applied plots indicates the beneficial effects of theamendment in the form of (1) improved ionic balance in the soil interms of the relative ratios of Ca2+ and Mg2+ and decrease in EMPlevels (Fig. 2); (2) enhanced nutrient availability status in the soilthrough increased levels of phosphorus and potassium as observedin other studies under similar conditions (Vyshpolsky et al., 2008);and (3) enhanced water movement and storage in the soil vis-à-visgreater water availability to the plants (Fig. 3).

3.7. Economics of applied treatments

The expenditures on fertilizer purchase and application as wellas on water supply and irrigation application differed between theyears, but were the same for all treatments in each year, i.e. 2006and 2007 (Table 5). The cost of producing cotton increased in thephosphogypsum treatments because of the purchasing, transporta-tion, and application costs of the amendment during the first year ofthe study. In 2006, the maximum total expenses (US$, later referredto as $) incurred were in the PG8.0–Jan treatment ($ 692), followedby PG8.0–Apr ($ 662), PG3.3–Jan ($ 528), PG3.3–Apr ($ 514), and control

sum application increased the net income from the PG3.3–Jan (US$166) and PG3.3–Apr treatments (US$ 92) whereas in control thisparameter was US$ 87. The net income from the PG8.0–Jan treat-ment (US$ 84) and control (US$ 87) was almost the same, while

arginal rate of return, other parameters are expressed in US$)a.

PG8.0–Jan PG3.3–Apr PG8.0–Apr

251 104 251323 293 293

23 23 2395 95 95

692 514 662776 606 600

84 92 –621.12 1.18 0.91

–1 3 –54

374.3 372.8 372.841.7 41.7 41.762.4 62.4 62.4

478.4 476.9 476.91050 1000 1000

572 523 5232.19 2.10 2.10

42 22 22

verted to US$ with the currency exchange rate in the respective year.ring the first year of the experiment in 2006; no amendment was applied in the

seed, sowing, weeding, harvesting, and transportation of the harvest material. Thensportation of the harvest material.he respective year.

ater M

nclPpi

iaedsiwrwT(tt

4

cstePtilvra

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F. Vyshpolsky et al. / Agricultural W

et income was negative in PG8.0–Jan treatment (US$ 62). Benefitost ratio under phosphogypsum-applied treatments in 2006 fol-owed a similar trend in the order: PG3.3–Jan (1.31), control (1.23),G3.3–Apr (1.18), PG8.0–Jan (1.12), and PG8.0–Apr (0.91). The unex-ected high velocity wind negatively affected cotton yield in 2006

n all treatments.In 2007, the total cost of the treatments was almost similar as

t did not include items for the purchasing, transportation, andpplication costs of phosphogypsum. This increased the net ben-fits from the phosphogypsum treatments, which were more thanouble the control treatment. While comparing the phosphogyp-um treatments, the net benefits from the amendment applicationn winter season (before snowmelt) were about $ 50 more than that

ith applications in spring (after snowmelt). The marginal rate ofeturn (MRR) was 42 in the case of phosphogypsum application ininter and 22 in the case of spring application of the amendment.

hese results suggest the lower rate of phosphogypsum application3.3 t ha−1) was superior to the higher rate (8.0 t ha−1). In addition,he amendment application before snowmelt was more beneficialhan that in spring season after snowmelt.

. Conclusions and perspectives

The results of this 2-year field study demonstrate the benefi-ial effects of phosphogypsum application to a magnesium-affectedoil. The amendment was applied to the respective treatments atwo rates (3.3 and 8.0 t ha−1) once at the beginning of the studyither in January (PG3.3–Jan and PG8.0–Jan) or in April (PG3.3–Apr andG8.0–Apr). The phosphogypsum treatments performed better thanhe typical farming practice in terms of (1) improved soil qual-ty through a reduction in exchangeable magnesium percentageevels; (2) enhanced water movement into and through the soilis-à-vis increased moisture storage in the soil for use by the plantoots; (3) increased irrigation efficiency; (4) increased cotton yieldnd water productivity; and (5) greater financial benefits.

Based on the overall effects, the amendment application beforehe snowfall improved soil properties to a greater extent com-ared to the application in spring after the snowmelt. The economicenefits in terms of marginal rate of return from phosphogypsumpplication at 3.3 t ha−1 were double those of treatments receivinghe amendment at 8.0 t ha−1, thereby suggesting that the lower rateas optimal. This rate of phosphogypsum application is based on

he phosphogypsum requirement of the soil for 0.3 m depth.There are more than 140,000 ha in southern Kazakhstan char-

cterized by soils with high levels of magnesium and low cottonields (1–1.4 t ha−1). The use of a Ca2+ supplying amendments suchs phosphogypsum has the potential to increase cotton yield sub-tantially and livelihoods of the smallholders, which occupy mostf land in the area. As a source of Ca2+, phosphogypsum is availablen southern Kazakhstan and other parts of Central Asia that can besed to enhance cotton productivity. After the successful on-farmrials in southern Kazakhstan, the phosphogypsum technology haseen out-scaled to more than 100 ha during the project implemen-ation phase. The collaborating farmers contributed 30% cost of theechnology. Other farmers in the region have largely indicated theirillingness to adopt the use of phosphogypsum for the productivity

nhancement of magnesium-affected soils.In addition to technology transfer, we have also helped the inter-

sted farmers in determining the phosphogypsum requirement ofheir soils for the optimal rates of the amendment application. The

elated institutions from Kazakhstan are working on mechanismsor supplying phosphogypsum to farmers at the minimum possi-le transportation cost, which is the major expenditure involved inhosphogypsum delivery as the phosphogypsum stocks are about00 km away from the area where magnesium-affected soils occur.

anagement 97 (2010) 1277–1286 1285

Acknowledgments

This publication is a part of the joint initiative of the Interna-tional Center for Agricultural Research in the Dry Areas (ICARDA)and International Water Management Institute (IWMI) address-ing the assessment and management of marginal-quality waterresources and salt-affected soils. We are grateful to the Asian Devel-opment Bank for providing financial support for this study underthe Regional Technical Assistance (RETA 6208) project entitled“Enabling communities in the Aral Sea Basin to combat land andwater resource degradation through the creation of ‘Bright’ spots”.

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