Agricultural erosion research has focused on rainfall-induced soil loss, with comparatively little attention to furrow
irrigation-induced erosion. One rationale for this is that rill erosion is mechanistically similar to erosion in irrigated
furrows. However, significant differences exist between the two processes. These are related to soil conditions during
initial stream advance, downstream flow rates, and chemical characteristics of the water stream. The salinity and
sodicity of water in rills are low, owing to its atmospheric origin, whereas, irrigation water quality varies geographically
and seasonall

Carter, D.L.

Lentz, R.D.

Sojka, R.E.

USDA - ARS - NWISRL

INFLUENCE OF IRRIGATION WATER QUALITY ON SEDIMENT LOSS FROM FURROWSR. D. Lentz, R. E. Sojka and D. L. Carter, Soil and Water Management Research Unit:, USDA Agricultural ResearchService, Kimberly, IDINTRODUCTIONAgricultural erosion research has focused on rainfall-induced soil loss, with comparatively little attention to furrowirrigation-induced erosion. One rationale for this is that rill erosion is mechanistically similar to erosion in irrigatedfurrows. However, significant differences exist between the two processes. These are related to soil conditions duringinitial stream advance, downstream flow rates, and chemical characteristics of the water stream. The salinity andsodicity of water in rills are low, owing to its atmospheric origin, whereas, irrigation water quality varies geographicallyand seasonally.Few studies directed at irrigation-induced erosion have attempted to determine how irrigation water quality influencesfurrow erosion. Previous research suggests that water chemistry may influence both soil erodibility and streamerosiveness. Clay dispersion and aggregate breakdown were enhanced as "rain water" electrical conductivity (EC)decreased (Agassi et al., 1981) and/or sodium adsorption ratio (SAR) increased (Velasco-Molina et al., 1971). But, thedispersive effect of higher SARs was significantly depressed at high ECs (Velasco-Molina et al., 1971). Furrow surfacesbecome more erodible as clay dispersion increases and aggregate strength diminishes. These conditions also promotedevelopment of an impermeable depositional seal at the soil/water interface (Shainberg and Singer, 1985). Soils with<20% clay are most sensitive to seal formation (Ben-Hur et al., 1985). Southern Idaho's irrigated soils generally havelow clay contents. In these soils, infiltration in irrigated furrows is largely controlled by deposition of slowly permeablesurface seals (Brown et al., 1988; Segeren and Trout, 1991). Rapid formation of surface seals increases flow and, hence,stream erosiveness (at constant inflow rates).We hypothesized that irrigation water quality would impact sediment loss in furrows via affects on soil cohesionand infiltration. Water with low EC, or high monovalent ion concentrations (high SAR) should promote dispersion anddevelopment of a slowly permeable surface seal. This would decrease infiltration and increase stream velocity. Higherstream velocities stimulate detachment and sediment transport processes and increase soil loss from furrows. In addition,these solutions should weaken soil aggregates and decrease the soil's resistance to shear. High-EC/low-SAR water wouldimprove aggregate strength, promote flocculation and development of a more permeable surface seal, stabilize infiltration,and inhibit soil removal and transport processes. In 1991, we conducted a field study to test this hypothesis. This paperpresents preliminary results from that investigation.METHODSThe study was conducted near Kimberly, Idaho, on a 1.6 ha field of fallow Portneuf silt loam (coarse-silty, mixed,mesic, Durixerollic Calciorthids). Slope was 1%, furrow spacing was 0.76 m, and furrow length was 114 m. Four waterquality treatments consisted of combinations of the following relative levels: low (0.5 dS m-') or high (2 dS m -') EC,and low (0.7) or high (12) SAR. Water chemistry of furrow streams was adjusted by injecting solutions of NaOH,CaC12, and NaC1 into inflows. The control treatment employed nontreated irrigation water and represented the low-EC/low-SAR water quality group.Six experiments were run during the 1991 irrigation season. In each, four water quality treatments were applied totwo furrow types (wheel track and nonwheel track). The eight treatment combinations were replicated three times ineach experiment. Furrows in each experiment were given an initial irrigation and a single repeat irrigation 7-9 days later;thus 288 furrows were monitored in twelve irrigations from June through August. Inflow rate was 19 L min' for allirrigations except for the initial irrigation in the last three experiments; inflow was increased to 23 L min' during theseirrigations to promote more rapid furrow stream advance across the drier surface soils in these plots. Runoff wasmeasured using long-throated flumes installed at furrow outflows, and assessed sediment in tail-water samples usingthe Imhoff cone technique (Sojka et al., 1992).Analysis of variance (ANOVA) followed by Waller-Duncan tests for mean separation (a = 0.05) were used tocompare treatment effects. The error bars in treatment-comparison figures represent 95% confidence intervals.RESULTS AND DISCUSSIONThe initial analysis employed data from all irrigations and furrow types to test soil loss response to water qualitytreatments (Fig. 1). Sediment loss for control furrows was 2.53 Mg ha' and was not significantly different from thatof furrows irrigated with high-EC/high-SAR water. Soil loss from furrows irrigated with low-EC/high-SAR water was177% greater than that of control (low-EC/low-SAR) furrows. Soil lost from furrows irrigated with high-EC/low-SARwater was 70% less than from control furrows.274Note that net furrow infiltration, or intake, was greatest (Fig. 2) for those treatments that had the lowest soil losses(Fig. 1). These data suggest the possibility that an inverse relationship exists between intake and furrow erosion. Thenegative correlation between these factors became evident when all furrows were plotted as a function of net infiltrationand soil loss (Fig. 3). The relationship was confirmed via an overall regression analysis (P < 0.001). This evidencesupports our hypothesis that irrigation water quality influences furrow erosion through effects on stream erosivity, i.e.soil and aggregate dispersion promotes formation of an impermeable seal, which reduces furrow intake and increasesstream velocity. In addition, the weakening of furrow aggregates and increased soil dispersion under low EC and/or highSAR conditions promoted entrainment of sediment in the furrow stream and contributed to increased soil loss. 	 :-Soil loss for a given treatment varied significantly depending on irrigation type (initial/repeat) and furrow type(nonwheel track/wheel track), but the relationship between water quality treatments remained the same as in the overallanalysis. Soil kwaP--s for initial and repeat irrigations using 19 L min -1 inflows (Fig. 4) differed for each water qualitytreatment, with greater furrow soil losses from repeat irrigations than from initial irrigations. Wetter soils in furrowsduring repeat irrigations adsorbed less water than soils in the initial irrigation (Table 1). The resulting runoff and streamvelocity increase in the repeat furrows may account for the higher soil losses.Soil losses from wheel- and nonwheel-track furrows (19 L min t inflows) are presented in Fig. 5. Again, thesediment-loss pattern among water quality treatments was the same for wheel- and nonwheel-track furrows, and identicalto the overall analysis (Fig. 1). However, wheel-track furrows generally experienced greater sediment lossps thannonwheel-track furrows. These compacted furrows had lower water intake. The resulting increase in furrow streamvelocities magnified flow-induced erosion.REFERENCESAgasai, M., L Sheinberg, and J. Morin. 1981. Effect of electrolyte concentration and soil sodicity on the infiltration rate and crust formation. Soil Sci.Soc. Am. J. 45:848-851.Ben-Hur, M., L Sheinberg, D. Bakker, and R. Keren. 1985. Effect of soil texture and CaCO, content on water infiltration in crusted soil as relatedto water salinity. Irrig. Sci. 6:281-294.Segeren, A. G. and T. J. Trout. 1991. Hydraulic resistance of soil surface seals in irrigated furrows. Soil Sci. Soc. Am. J. 55:640646.Sheinberg, L and M.J. Singer. 1985. Effect of Electrolytic Concentration on the Hydraulic Properties of Depositional Crust. Soil Sci. Soc. Am. J.49:1260-1263.Sojla, R. E., D. I.. Carter, and M. J. Brown. 1992. Imhoff cone determination of sediment in irrigation runoff. Soil Sci. Soc. Am. J. 56:884-890.Velesco-Molina, H.A., A.R. Swoboda, and C.L Godfrey. 1971. Dispersion of soils of different mineralogy in relation to sodium adsorption ratio andelectriytic concentration. Soil Science 111:2132-287.2757,—..,'co	 620)2U)ca0_1r5	 1u)05432q Low EC/Low SAR 0 Low EC/High SARO High EC/Low SAR q High EC/High SARWater Qualityq Low EC/Low SAR 0 Low EC/High SARO High EC/Low SAR 0 High EC/High SARFigure 1. Overall influence of water quality on furrow soil loss (mean of 72 furrows).Water QualityFigure 2. Overall influence of water quality onnet infiltration in furrows (mean of 72 furrows).EEC0co.,..4-..6tiz120100806040200276'5u)100 Low EC/Low SAR 0 Low EC/High SAR0 High EC/Low SAR 0 High EC/High SAR20Initial	 RepeatWater QualityFigure 3. Relationship between net infiltration and sediment loss of all monitored furrows.Net Infiltration (mm)Figure 4. Furrow soil loss for irrigation type and water quality treatment combinations with 91 L min' inflows (means18-36 furrows).277r .Figure 5. Furrow soil loss for furrow type and water quality treatment combinations with 19 L min' inflows (mean offr..- 27 furrows).                     Low EC/Low SAR Low EC/High SAR          0 High EC/Low SAR 121 High EC/High SAR        072O•_1086NonWheel	 WheelWater Quality278

Influence of irrigation water quality on sediment loss from furrows

Northwest Irrigation & Soils Research Laboratory Publications

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Influence of irrigation water quality on sediment loss from furrows

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