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Field determined hydraulic properties of a sandy loam soil irrigated with various salinity and SAR waters

1994; Elsevier BV; Volume: 25; Issue: 2 Linguagem: Inglês

10.1016/0378-3774(94)90038-8

1873-2283

P.S. Minhas, R.K. Naresh, C. P. S. Chauhan, Rajeev Gupta,

Soil Moisture and Remote Sensing

Changes in the infiltration, drainage, soil-water characteristics and unsaturated hydraulic conductivity were evaluated in field plots of a sandy loam soil irrigated with waters of different salinities (ECw 6 and 12 dS·m−1) and sodium adsorption ratios [SARw 5, 20 and 40 (mmol.·1−1)12] for a period of 8 years. Unsaturated hydraulic conductivity, K(θ), for the various treatments was determined by measuring hydraulic gradients and soil-water contents from simultaneously evaporating and draining profiles, as well as from draining profiles with no evaporation. Relative infiltration rate (RIR) was calculated considering steady infiltration in the original soil (22.5 mm·h−1) as the reference relationship. When measured using canal water (ECw 0.7 dS·m−1), RIRs were reduced to 0.64–0.90, 0.10 and 0.05–0.07 in soils irrigated with SARw 5, 20 and 40, respectively. Long-term use of higher salinity waters but with similar SARs caused greater deterioration. When waters of various salinities and SARs were used for measuring infiltration, the RIRs at SARw 5, 20 and 40 (mmol·1−1)12 were increased to 0.96, 0.79 and 0.42 in soils irrigated with ECw 6 dS·m−1. Likewise, RIRs were increased to 0.67, 0.35 and 0.27 for an ECw of 12 dS·m−1. Stability of the surface soil and thus permeability should have improved during infiltration of saline waters with electrolytic concentrations more than the flocculation values, but the small improvement in infiltration rates indicate that deeper soil controls the steady infiltration rate. The dispersed state of the deeper layers in soils irrigated with high SAR waters was further evident from increased soil-water retention at lower matric potentials in the tensiometric range, as well as being reflected in decreased values of drainage coefficients and increased soil-water storage. Unsaturated hydraulic conductivity K(θ), could be adequately described (r = 0.87–0.97) by the equation K = α exp·(βθ). Values of K(θ), when referenced to the original soil, ranged between 0.56 and 1.12 at θ = 0.3 but were reduced 2- and 4-fold at θ = 0.1 m3·m−3 for soils irrigated with waters of SARw = 20 and 40 (mmol·1−1)12, respectively. Results indicate that the laboratory determinations may not assess adequately the changes in hydraulic properties upon irrigation with high-SAR saline waters in soils undergoing cycles of salinization and desalinisation under a continental monsoon climate.