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Irrigation Water Quality, SoilAmendment, and Crop Effectson Sodium LeachingJ. W. Bauder & T. A. BrockPublished online: 30 Nov 2010.
To cite this article: J. W. Bauder & T. A. Brock (2001) Irrigation Water Quality,Soil Amendment, and Crop Effects on Sodium Leaching, Arid Land Research andManagement, 15:2, 101-113, DOI: 10.1080/15324980151062724
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Arid Land Research and Management, 15:101± 113, 2001Copyright Ó 2001 Taylor & Francis1532-4982/01 $12.00 ‡.00
Irrigation Water Quality, Soil Amendment, andCrop E� ects on Sodium Leaching
J. W. BAUDERDepartment of Land Resources and Environmental SciencesMontana State UniversityBozeman, Montana, USA
T. A. BROCKINEEL Research Center (IRC)Idaho Falls, Idaho, USA
Due to prolonged irrigation with water of marginal quality, salination of irrigatedsoils in some areas of southeastern Montana has led to a need for better under-standing of the soil and water management alternatives for irrigators. A study wasconducted with Haverson silty clay ( ® ne-loamy, mixed, calcareous, mesic UsticTorri¯ uvent) to determine the e� ect of combinations of chemical amendments,crop species, and irrigation water quality on Na‡ and salt leaching from salt-a� ected soils. Amendments included CaSO4, P-CaSO4 and MgCl2; also includedwas a nonamended control treatment. Crops included alfalfa (Medicago sativa L .),barley (Hordeum vulgare L .), sorghum-sudangrass [(Sorghum vulgare Sorghumdrumondii) (sordan)], and a noncropped control. All soil columns (0.15 m 0.5 m)were irrigated with either high Na‡ adsorption ratio (SARadj ˆ 16:6), high totaldissolved solids (TDS ˆ 1647 mg L ¡1) water, or low SARadj (1.15), low TDS (747mg L ¡1) water. Drainage volume, electrical conductivity (EC), SAR, Na‡ ofdrainage water, and Na‡ leaching were monitored over three crop cycles.Irrigation with high SAR-high TDS water increased the soil solution EC to approxi-mately 5.5 dS m¡1, but did not decrease crop yields relative to irrigation waterhaving SARadj and TDS of 0.37 and 747 mg kg¡1, respectively. Magnesium dis-placed Na‡ on the exchange complex, but the e� ects were short-term compared toCaSO4 or P-CaSO4. Amendments increased yields of barley from 14% ± 27% andalfalfa by 25% but had no e� ect on sordan. Columns cropped to barley had 28%greater Na‡ leaching than columns planted to other crops. Noncropped columnsaccumulated the least net soluble salt and Na‡. Results of this study demonstratethat speci® c crop and amendment combinations can signi® cantly a� ect the e� ciencyof saline soil reclamation strategies and impact quality of irrigation return ¯ ow.
Keywords salinity, gypsum, sodium adsorption ratio, electrical conductivity,soil reclamation
Abbreviations SARÐ sodium adsorption ratio, TDSÐ total dissolved solids,ECÐ electrical conductivity, ESPÐ exchangeable sodium percentage, CECÐcation exchange capacity, WQ1Ð past irrigation water quality, WQ2Ð future irri-gation water quality
Received 19 July 2000; accepted 28 August 2000.Address correspondence to Dr. James W. Bauder, Soil and Water Quality Specialist, Department of
Land Resources and Environmental Sciences, Leon Johnson Hall, Montana State University, PO Box173120, Bozeman, Montana 59717-3120 , USA. E-mail: [email protected]
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The Powder River drains approximately 34,700 km2 of northeastern Wyoming andsoutheastern Montana. Nearly 4,500 ha in Montana are irrigated with Powder Riverwater. The geology of the basin which Powder River drainage includes some igneousand metamorphic rocks but the vast majority of the basin is underlain by sedimentsof marine origin, including limestone, sandstone, gypsiferous shales, and siltstones.The combination of low precipitation (<350 mm annually) and marine sedimentsproduces stream¯ ow with high concentrations of total dissolved solids (TDS). Totaldissolved solids and Na‡ content of the Powder River have increased 10% to 30%over the past 20 years (Lowry and Wilson, 1986). In addition, salination of irrigatedsoils along the Powder River in Montana has occurred (Gallagher, 1986).
E� cient, economically feasible soil reclamation strategies are necessary toreverse deteriorating soil conditions associated with long-term irrigation by waterof relatively high TDS concentration and SARs (Francois, 1981). Because Na‡
saturation and clay dispersion are often associated with salination, present reclama-tion e� orts focus on replacing soil-adsorbed Na‡ with Ca2‡ or Mg2‡, both of whichcontribute to aggregate stability and improved drainage. Many researchers haveproposed Ca2‡- or Mg2‡-rich chemical amendments for sodic soil reclamation(Dollhopf, 1988; U.S. Salinity Laboratory Sta� , 1969). Various crops also havebeen reported to improve permeability and promote removal of Na‡ and saltfrom the soil (Robbins, 1986).
Reclamation of sodic soils requires that water penetration into and through thesoil be improved by either (1) exchanging excess Na‡ with Ca2‡ or Mg2‡ to facilitateleaching, or (2) initially leaching with saline water and then progressively decreasingsalinity of the applied water (Ho� man, 1986). Reclamation of saline-sodic and sodicsoils should decrease soil exchangeable sodium percentage (ESP) and pH to improvesoil physical conditions, improve soil nutrient status, and remove soluble salts fromthe soil by leaching. Removal of soluble salts from saline-sodic soil without a corre-sponding decrease in ESP will result in a sodic soil, while only decreasing ESP mayproduce a soil solution of greater salt concentration (Cates, 1979). When both salineand nonsaline waters are not available and deep tillage will neither provide adequatedilution through soil mixing nor improve in® ltration and drainage, addition of anamendment is necessary.
The objective of this study was to determine e� ects of soil amendments, cropspecies, and irrigation water quality on soil solution chemistry, crop yields, andchemical composition of leachate by assessing crop yield performance and charac-terizing composition and changes in soil solution chemistry as a function of time anddepth in soil columns through a cycle of 15 irrigations.
Materials and Methods
Construction of Soil Columns and Experimental Design
Soil used in this greenhouse study was Haverson silty clay ( ® ne-loamy, mixed calcar-eous, mesic Ustic Torri¯ uvent) (Soil Survey Sta� 1998), collected from the 0± 0.25 mdepth of an irrigated alfalfa (lucerne, Medicago sativa L.) ® eld adjacent to thePowder River in southeast Montana (45.1758N, 105.8258W). The ® eld had a priorhistory of 20+ years of irrigation with Powder River water. This soil was selected forstudy because the soil series represents approximately 60% of the irrigated acreage inthe Powder River Basin and had been previously identi® ed as experiencing crop yieldreductions due to salination (Gallagher, 1986). Details of column construction andpreexperiment soil properties were reported previously (Bauder and Brock, 1992) andare summarized in Table 1. The columns, measuring 0:15 m 0:5 m, were packedwith dry soil to a uniform bulk density of 1.07 Mg m¡3, wet to saturation with watersimulating existing median ¯ ow-weighted Powder River quality (Lowry and Wilson,1986), and then drained (Table 2).
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The columns were then arranged as a 4 4 2 complete factorial, randomizedblock design, with three replications. Main treatments included three crop speciesand a noncropped control, three surface-applied soil amendments and a nontreatedcontrol, and two irrigation water qualities, representing `̀ past’ ’ (WQ1) and antici-pated `̀ future’ ’ (WQ2) irrigation water qualities. Irrigation water constituents andcriteria were based on historic Powder River water quality data and trends, analyzedand reported by Dalby (1988) and presumed to have a consequence of increasingTDS levels of irrigation water due to upstream oil and natural gas well development.Ionic speciation analyses were performed for the intended water qualities to ensurethat the irrigation waters were not supersaturated with respect to CaCO3. Waterquality of both irrigation sources is summarized in Table 2.
Amendment treatments included (1) CaSO4 12.9 Mg ha¡1, (2) P-CaSO4, 12.8Mg ha¡1, (3) MgCl2 10.5 Mg ha¡1, and (4) no amendment (control). Phospho-gypsum consists of 80± 99% CaSO4, mineral impurities, and less than 1% PO3¡
4(Keren and Shainberg 1981). The amendments were applied to the soil surfaceand incorporated by mixing the soil to a depth of 0.1 m. These rates were determinedto be needed to reduce the ESP of the preexperiment soil by 7%, i.e., essentiallyreplacing all of the exchangeable Na‡ throughout the length of the columns. Croptreatments included: alfalfa (Medicago sativa L.), var. `Ladak 65’ ; barley (Hordeumvulgare L.), var. `Steptoe’ ; and sorghum-sudangras s [Sorghum vulgare Pers.Sorghum drummondii) (sordan) (Steudel) Millsp. & Chase], var. `Sordan 79’ .Sorghum-sudangras s is commonly referred to as sordan.
Three successive barley crops were grown. Alfalfa and sordan were planted atthe beginning of the experiment and regrowth was repeatedly harvested. All cropswere harvested when barley reached the soft dough stageÐ growth stage 11.2 (Large,
Amending and L eaching Sodic Soils 103
TABLE 1 Physical and chemical properties of preexperimentHaverson silty clay
Property Preexperiment value
EC 2.47 dS m¡1
SAR 5.36Saturation water content 0.68 m3 m¡3
Bulk density 1.07 Mg m¡3
pH 8.27Exchangeable sodium percentage (ESP) 6.9%Cation exchange capacity (CEC) 24.7 cmolc kg¡1
Alkalinitya 208 mg kg¡1
CaCO3 content 5:2 10¡3 kg kg¡1
a Alkalinity measured in the form of HCO¡3 .
TABLE 2 Ionic composition and chemical criteria of irrigation water treatments
Constituent
TotalWater Ca2‡ Mg2‡ Na‡ K‡ Cl¡ HCO¡
3 SO2¡4 dissolved
quality solids ECtreatment mg kg¡1 ds m¡1 SAR SAR…adj† pHcmol L¡1
WQ1 0.50 0.33 0.24 0.03 0.09 0.23 0.77 747 0.97 1.15 2.5 8.3WQ2 0.50 0.40 1.49 0.02 0.55 0.38 1.48 1647 2.21 2.22 16.6 8.5
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1954), coinciding with each ® fth irrigation, for a total of three harvests and 15irrigation events.
Drainage Water and Posttreatment Soil Analyses
Water was applied at two-week intervals. The entire study lasted approximately 30weeks beyond initial conditioning of the soil columns and crop establishment.Columns were weighed before each irrigation, and average evapotranspiration wascalculated for each crop to determine the amount of water necessary to achieve thedesired leaching fraction. Each column was individually irrigated, using a supplyreservoir and a drip emitter to provide a constant leaching fraction of approximately0.1 to all columns. Following crop establishment, all drainage water was collectedfrom each column after each irrigation. Leachate volume, electrical conductivity(EC), and Na‡ of all leachate samples were measured. Drainage water was analyzedfor SAR following selected irrigation events. Drainage water analyzed for alkalinitywas collected in plastic bags sealed to drainage tubes to prevent precipitation ofCaCO3. Alkalinity in the form of HCO¡
3 and pH were measured within 24 hoursof leachate collection. Following the third crop cycle, soil from 0± 0.05 m, 0.2± 0.25 m,and 0.4± 0.45 m depths of each column was sampled and analyzed to determinepostexperiment soil saturated paste extract EC and SAR.
Statistical Analyses
Statistical analyses were performed using SAS (Statistical Analysis System, 1998).Analysis of variance for a three-way interaction of irrigation water quality, soilamendment, and crop was performed on all data. In addition, analyses of variancewere performed for two-way interactions for drainage water quality and crop yield.Analyses of variance were performed to determine signi® cance of di� erences ofpostexperiment soil chemical data by depth and by crop depth.
Due to missing data, the General Linear Models (GLM) procedure was used foranalysis of variance; Duncan’s Multiple Range Test was used for comparisonsamong treatment means.
Results and Discussion
Na‡ and Salt Leaching
E� ciency of treatments for removing Na‡ from the soil was evaluated as mmoleNa‡ leached per pore volume of leachate (Figure 1 and Figure 2). Data pointscoincide with irrigation events and represent gross or total amount of Na‡ or saltleached from the columns, i.e., the values have not been adjusted to account for theamount of Na‡ or salt added with irrigation water.
Irrigation with water having SARadj ˆ 16:6 and TDS ˆ 1647 mg L¡1 signi® -cantly (P ˆ 0:05) increased concentration of Na‡ in drainage water relative to e� ectsof irrigation with water having SARadj ˆ 1:15 and TDS ˆ 747 mg L¡1. This increasein Na‡ concentration was a re¯ ection of additional salt load to the soil and drainagewater from irrigation with the more sodic and more saline WQ2 and displacement ofNa‡ from the soil exchange complex. The preexperiment soil SAR was 5.36, with anassociated ESP of 6.9%.
AmendmentsMagnesium chloride resulted in greater Na‡ leaching throughout the experiment
than treatment with the other amendments or the control for all crops except barley(Figure 2). Amendments had no signi® cant cumulative e� ect on Na‡ leaching whenapplied to columns planted to barley, although columns planted to barley and
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Amending and L eaching Sodic Soils 105
FIGURE 1 E� ect of irrigation water quality, amendment, and crop species onNa‡ leaching. (Values averaged over interactions. Treatment means followed bythe same letter are not signi® cantly di� erent at P ˆ 0:05, according to Duncan’sgrouping.)
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treated with MgCl2 initially had signi® cantly greater Na‡ leaching than the non-treated columns. On the basis of the cumulative amount of Na‡ leached from thecolumns treated with MgCl2, it appears that the MgCl2 was almost completelydissolved and either exchanged or leached from the columns cropped to barley bythe end of the ® fth irrigation. Leaching of MgCl2 out of the columns also mayexplain the decline in Na‡ leaching over time from columns planted to barley andtreated with MgCl2.
CaSO4 and P-CaSO4 treatments caused signi® cantly greater …P < 0:05) Na‡
leaching than the control treatment, but they did not di� er signi® cantly from eachother.
CropsColumns planted to barley had signi® cantly greater (P < 0:05) Na‡ leaching
than the other cropped columns, although the Na‡ leaching decreased over time.
106 J. W . Bauder and T . A. Brock
FIGURE 2 E� ect of irrigation water quality or amendment on Na‡ leaching withincrop treatments. (Values averaged over interactions.)
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Columns planted to sordan had the least Na‡ leaching throughout the experiment.Sodium removal from columns planted to alfalfa was similar to that from the non-cropped treatment during the ® rst harvest cycle. However, by the last harvest cycleNa‡ leaching from columns planted to alfalfa was greater than from columnsplanted to barley. The increases in Na‡ leaching with time of columns planted toalfalfa was most likely a consequence of the alfalfa becoming established and tran-spiration increasing.
Columns planted to alfalfa and treated with P-CaSO4 or CaSO4 had signi® -cantly greater (P < 0:05) Na‡ leaching than the control columns. Within the alfalfacrop, all amendments increased Na‡ leaching above the control treatment. However,as the leachate volume increased, P-CaSO4 caused greater Na‡ leaching than CaSO4or the control treatment in columns cropped to barley or noncropped. Noncroppedcolumns had moderately high Na‡ leaching. High water contents most likelyrestricted the extent to which salt precipitation occurred and promoted ¯ ushing ofNa‡ from the soil.
Sodium Adsorption Ratio of Drainage Water
Main treatment e� ects on SAR of the drainage water are shown in Figure 3. As wasexpected, SAR of leachate from columns irrigated with WQ2 was signi® cantlygreater (P < 0:05) than SAR of leachate from columns irrigated with WQ1. SARof the drainage water increased over the duration of the study. The SAR of drainagewater from columns irrigated with either water source became greater than the SARof the preexperiment saturated soil extract or the irrigation water, indicatingpreferential leaching of Na‡ or exchange of Ca2‡ and Mg2‡ in the soil solutionwith exchangeable Na‡.
AmendmentsAddition of MgCl2 caused drainage water SAR to increase to a value signi® -
cantly greater than that caused by addition of the other amendments. However, bythe seventh irrigation SAR of the drainage water from columns treated with MgCl2was signi® cantly less than the SAR from columns treated with other amendments orthe control. The SAR of leachate at the end of the experiment from no-amendmenttreatments was greater than the SAR of the applied irrigation water, re¯ ecting theSAR of the saturated soil solution extract prior to the study. Addition of P-CaSO4 orCaSO4 a� ected SAR of drainage water only slightly and irregularly, relative to thecontrol treatment. This lack of response is indicative of the slow dissolution rates ofP-CaSO4 or CaSO4, the relatively high CaCO3 concentrations in the study soils, andthe resultant ine� ectiveness of either of these amendments for displacing Na‡
(Robbins, 1986).
CropsThe SAR of drainage water from columns planted to barley increased sig-
ni® cantly over the ® rst seven irrigations, relative to the SAR of drainage waterfrom columns planted to other crops (Figure 3). Barley caused release of moreNa‡ from the soil than did the other crops. The barley crop without the additionof amendments resulted in leaching of more Na‡ (relative to Ca2‡ and Mg2‡ perequivalent pore volume of leachate) than the other crops in the absence of anamendment. The noncropped and sordan treatments had lower drainage waterSARs than the barley or alfalfa treatments during much of the experiment.
The SAR of drainage water from columns planted to alfalfa increased over timeafter the eighth irrigation. This gradual increase in SAR may be a re¯ ection ofprogressively increasing vigor of the alfalfa crop as it became more establishedwith time. This corresponds to results found by Rhoades and colleagues (1973),
Amending and L eaching Sodic Soils 107
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indicating that drainage water salt concentrations and lime solubility are highestwhen alfalfa is rapidly growing and CO2 production by roots is high.
pH, Alkalinity, and pCO2 of Drainage Water
Alkalinity (HCO¡3 ) and pH of the drainage water were used to estimate CO2 con-
centration of drainage water (Stumm and Morgan, 1981). Treatments caused onlyminor di� erences in pH, alkalinity, or CO2 concentration (data not shown). Thislack of response to treatments was most likely due to the high bu� ering capacity ofthe soil. During the initial irrigations, pH of drainage water from columns treatedwith MgCl2 was signi® cantly lower than the pH of drainage water from the other
108 J. W . Bauder and T . A. Brock
FIGURE 3 E� ect of irrigation water quality, amendment, and crop species on SARof drainage water. (Values averaged over interactions.)
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treatments, due most likely to the initially high electrolyte concentration of drainagewater from MgCl2 treatments. Increasing salt concentration usually decreases pH bydisplacement of H‡ and Al3‡ by cations in solution, allowing Al3‡ to hydrolyze andfurther lower pH (Bohn, McNeal, and O’Connor, 1985).
Drainage water from the last irrigation of sordan or alfalfa had signi® cantly(P ˆ 0:05) lower pH and greater CO2 concentration than drainage from the non-cropped or barley treatments. This was probably due to the fact that both sordanand alfalfa were managed as perennial crops (repeated harvest), thus likely resultingin greater root biomass than the barley crop and also due to greater transpirationfrom these crops during the last crop cycle. This corresponds to results by Robbins(1986), who postulated that CO2 production by respiring plant roots can be corre-lated with rate of plant growth.
A calcite solubility plot for pCO2 ˆ 0:0033 kPa (atmospheric pCO2) and 0.033kPa (typical soil pCO2) with the -log(Ca) of drainage water plotted against pH onthe solubility diagram indicated that all drainage water was oversaturated withrespect to calcite at both levels of pCO2.
Treatment E� ects on Soil Chemistry
Accumulated Salt and Na‡
Main treatment e� ects on Na‡, SAR, and salt accumulation in the soil areshown in Table 3. It was assumed that the saturated paste extract EC re¯ ectedincreases or accumulation of salt within the soil. Soil SAR and salt concentrations(re¯ ected in EC data) at the end of the study indicated signi® cant di� erences(P ˆ 0:05) due to irrigation water quality, crop species, and amendment (Table 3).Poststudy soil salinity was consistent with drainage water characteristics. Soil SARdi� ered signi® cantly throughout the columns between water quality treatments.Accumulation of salts from irrigation with WQ1 was partially due to salts addedas amendments. However, columns which were not treated with an amendment alsohad net accumulation of salt for each crop, implying that the leaching fraction was
Amending and L eaching Sodic Soils 109
TABLE 3 E� ect of irrigation water quality, amendment, and crop species onpostexperiment soil saturated paste extract SAR and EC*
Sample depth, m
0± 0.05 0.2± 0.25 0.4± 0.45 0± 0.05 0.2± 0.25 0.4± 0.45Main factor (treatment) SAR EC ds m¡1
Water qualityWQ1 1.7b 3.0b 5.7b 2.5b 3.1b 4.3bWQ2 7.3a 7.5a 7.9a 4.1a 4.7a 5.7a
AmendmentControl 5.0a 5.7a 6.7b 2.8b 3.7c 4.5bCaSO4 4.1b 5.3ab 7.2ab 4.0a 4.2ab 5.5aP-CaSO4 3.7b 5.3ab 7.4a 4.1a 4.4a 5.4aMgCl2 4.8a 4.9b 5.8c 2.4b 3.6c 4.5b
Crop speciesControl 4.6a 3.6c 4.5d 4.1a 3.1c 3.6cAlfalfa 3.9b 6.1a 8.7a 2.8c 4.3a 6.2aSordan 4.6a 6.6a 7.8b 3.2b 4.7a 5.2bBarley 4.6a 5.0b 6.0c 3.1cb 3.7b 4.8b
* Values are main treatment means, averaged across interactions. Treatment means within acolumn followed by the same letter are not signi® cantly di� erent at P ˆ 0:05, according toDuncan’ s grouping.
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too low to prevent salt accumulation, even when the columns were irrigated withWQ1.
AmendmentsColumns treated with MgCl2 accumulated signi® cantly less …P ˆ 0:05† Na‡ than
columns treated with the other amendments or the control treatment. Total saltaccumulation in columns (re¯ ected in soil solution EC values) treated with eitherP-CaSO4 or CaSO4 was nearly twice as great as in columns treated with MgCl2 or noamendment. The MgCl2 had most likely dissolved and leached through the soil by theend of the experiment, while it is likely that much of the P-CaSO4 or CaSO4 remainedundissolved and hence did not contribute to improving drainage from the columns.
CropsVariations in net amount of water leached and transpiration among the crops
over time resulted in di� erences in both Na‡ and salt ¯ uxes. The noncropped treat-ment accumulated signi® cantly less Na‡ and salt than the cropped treatments. Thisoccurred because water use from the noncropped columns was insigni® cant andonly one-third the amount of water was applied and leached from the noncroppedtreatments than from the cropped treatments. Relatively greater water contents (dueto lack of plant water uptake) may have prevented signi® cant precipitation andaccumulation of salts as well as contributing to more soil P-CaSO4 weathering.Columns planted to sordan accumulated signi® cantly more Na‡ and salt than barleyor alfalfa treatments. Columns planted to barley accumulated slightly less Na‡ andsigni® cantly more salt than columns planted to alfalfa. The lowest SARs at thedeeper soil depths occurred in columns treated with MgCl2. Treatment withP-CaSO4 or CaSO4 appears to have increased SAR at the bottom of the columnsdue to Na‡ displacement at the surface and accumulation at lower depths. P-CaSO4or CaSO4 caused more complete and lasting reclamation than MgCl2, as evidencedby higher SARs in the surface of columns treated with MgCl2 than with P-CaSO4 orCaSO4 after several irrigations.
Columns with alfalfa had signi® cantly lower SARs in the surface 0.05 m than theother cropped columns and the control, while at the deeper depths the SARs variedfor the crop treatments in the following order: noncropped < barley < alfalfa ˆsordan. The elevated SAR and EC with depth in the soil may be a re¯ ection ofeither maximum depth of leaching, lack of adequate drainage, or failure to achieveequilibrium in the columns in the duration of the study.
Cropped columns had di� erent soil solution EC patterns than the noncroppedcolumns (Table 4). Columns cropped to barley had the lowest ECs of the croppedtreatments at the lower depths. Relatively high soil water contents in the noncroppedtreatments and columns cropped to barley probably contributed to the lower SARsand ECs of these treatments at the deeper depths. Conversely, evaporation from thesurface of these columns caused accumulation of salts near the surface. Insu� cientdrainage in ponded barley treatments and relatively small volumes of water appliedto the noncropped treatments may also have prevented downward movement ofsalts.
Crop and Water Quality InteractionsE� ects of water quality on distribution of salts in the columns varied among
crops. Soil EC near the surface of cropped treatments irrigated with WQ1 was nearlythe same as preexperiment soil ECs (when averaged over amendment treatments).The WQ2 treatment caused ECs to increase to values above preexperiment ECs at alldepths in all treatments. Soil EC of cropped treatments increased with depth whileEC of noncropped columns decreased in the mid and lower depths. The smallestdi� erences in postexperiment soil EC between water quality treatments were mea-sured in the noncropped treatments.
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E� ects of amendments on SAR varied between water quality treatments andamong crop species. Amendments had no signi® cant e� ect on SAR of columnsirrigated with WQ1 (data not shown). Magnesium chloride was less e� ective bythe end of the experiment than P-CaSO4 or CaSO4 at lowering SARs in the surfaceof soils irrigated with WQ2 (Table 4). P-CaSO4 or CaSO4 lowered surface soil SARvalues signi® cantly below the control treatments in columns cropped to alfalfa orsordan. SAR in the surface soil of columns treated with MgCl2 was similar to thesurface soil SAR in the columns with no amendment in all but the noncroppedtreatments. Addition of MgCl2 to noncropped columns resulted in SARs less thanthe SAR of columns to which no amendment was applied. Addition of MgCl2 causeda signi® cant reduction in SAR in the bottom one-third of all cropped columns, withexception of those cropped to barley.
For all but the noncropped treatments, P-CaSO4 or CaSO4 resulted in signi® -cantly greater ECs in the surface soil than in the surface soil of control treatmentsand columns treated with MgCl2.
Crop Yield
Yield data are presented in Table 5. For purposes of comparison and analysis,cumulative dry matter yield from the alfalfa columns was used as a standard. Allother cumulative yield values were expressed as a fractional representation of alfalfaand analyzed accordingly. Crop yields did not di� er signi® cantly between waterquality treatments. The increase in soil salinity caused by irrigation with WQ2
Amending and L eaching Sodic Soils 111
TABLE 4 E� ect of irrigation water quality crop species and waterquality amendment interactions on postexperiment soil saturated paste extractSAR and EC
Sampling depth, m
Treatment 0± 0.05 0.2± 0.25 0.4± 0.45 0± 0.05 0.2± 0.25 0.4± 0.45
Water quality SAR EC dS m¡1
Control 2.0aa 2.6a 4.2b 3.3a 2.7a 3.5b
WQ1 Alfalfa 1.0a 3.4b 8.3c 2.1a 3.4b 5.9cSordan 1.7a 3.9b 5.9c 2.4a 3.6b 4.1cBarley 1.5a 2.4a 4.2b 2.1a 2.6a 2.8b
Control 7.2a 4.5a 4.8a 4.9c 3.3a 3.9b
WQ2 Alfalfa 6.6a 8.9c 9.1c 3.5a 5.2b 6.6cSordan 7.6a 9.2c 9.7b 4.1a 5.8b 6.3cBarley 7.8a 7.4b 7.9a 4.0a 4.7b 6.0c
Control 7.2a 4.5a 4.8a 4.9c 3.3a 3.9b
WQ2 Alfalfa 6.6a 8.9c 9.1c 3.5a 5.2b 6.6cSordan 7.6a 9.2c 9.7b 4.1a 5.8b 6.3cBarley 7.8a 7.4b 7.9a 4.0a 4.7b 6.0c
Control 2.0a 3.6b 5.5b 8.2b 7.7b 7.7a
Amendmentb CaSO4 1.5a 3.1b 5.7b 6.8a 7.3a 8.5cP-CaSO4 1.5a 2.8b 6.3c 6.0a 7.9b 8.5cMgCl2 1.6a 2.8b 4.7a 8.1b 7.2a 7.0a
a Treatment means within a column followed by the same letter are not signi® cantly di� er-ent at P ˆ 0:05, according to Duncan’s grouping.
b Data presented for interactive e� ect of WQ2 only; e� ects due to WQ1 amendment didnot di� er signi® cantly at P ˆ 0:05, according to Duncan’s grouping.
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reduced crop water use but did not cause signi® cant yield decreases. Addition ofMgCl2 or P-CaSO4 caused barley yields to be signi® cantly greater than the barleyyields from control treatments. Barley yield decreased dramatically after the ® rstharvest. The decrease appeared to be a direct result of surface ponding and poor rootaeration, as soil structure deteriorated over the course of the experiment (Bauder andBrock 1992). All amendments increased alfalfa yields. Amendments reduced sordanyields slightly but not signi® cantly.
Sordan yields decreased over time. Drought stress from decreasing osmoticpotential may have occurred in the sordan crop to a greater degree than in othercrops and may have contributed to the decline in sordan yield.
Conclusions
Irrigation with moderately high SARadj and high TDS water, simulating anticipatedfuture Powder River quality, caused signi® cant increases in salt concentration andSAR of soil and drainage water, resulting in reclassi® cation of the soil to saline (U.S.Salinity Laboratory Sta� , 1969). Irrigation with water of relatively low SARadj andlow TDS caused soil SARs to decrease to less than pretreatment soil SARs.However, leaching fractions were not great enough to prevent salt accumulation.Irrigation water quality did not signi® cantly a� ect crop yield.
E� ect of amendments on Na‡ leaching corresponded to amendment dissolutionrate, i.e., MgCl2 > P-CaSO4 > CaSO4. Bene® cial e� ects of MgCl2 appeared to beshort term, relative to the duration of e� ects of P-CaSO4 or CaSO4 on soil proper-ties. This was most likely due to the rapid leaching of MgCl2 from the soil and easierreplaceability of Mg2‡ than Ca2‡ from the cation exchange complex.
Soil solution EC of columns treated with P-CaSO4 or CaSO4 was elevated,relative to EC of soil solutions from columns treated with MgCl2 or the control.Treatment with MgCl2 elevated the EC of leachate to a higher value than as a resultof treatment with the other amendments. Columns without a crop accumulated theleast net soluble salt and Na‡.
References
Bauder, J. W., and T. A. Brock. 1992. Crop species, amendment, and water quality e� ects onselected soil physical properties. Soil Science Society of America Journal 56:1292 ± 1298.
112 J. W . Bauder and T . A. Brock
TABLE 5 E� ect of soil amendment on relativecumulative dry matter yield (values presented areaverage of WQ1 and WQ2 treatments)
Crop species
Amendment Alfalfa Sordan Barley
Cumulative yield, % of controlControl 100b* 100a 100bCaSO4 126a 92a 114abP-CaSO4 125a 92a 122aMgCl2 128a 93a 127a
* Treatment means followed by the same letter are not sig-ni® cantly di� erent at P ˆ 0:05, according to Duncan’s group-ing. Cumulative yield, % of control ˆ 100% ‰specified cropcumulative dry matter yield/cumulative alfalfa dry matter yield].
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