Infiltration of water in disturbed soil columns as affected by clay dispersion and aggregate slaking

Abstract

Soil crusting negatively affects the productivity and sustainability of irrigated agriculture, reducing water infiltration and plant emergence, and enhancing surface runoff and erosion. Clay dispersion and slaking of the aggregates at the soil surface are the main processes responsible for crusting. The infiltration rates (IR) of ten arid-zone soils in disturbed soil columns were measured and their relative susceptibilities to dispersion and slaking were determined. It was also examined whether the final soil IRs (FIR) could be estimated from various soil stability indices. The susceptibility to chemical dispersion was determined by measuring the IR of soil columns slowly pre-saturated from below with tap water and subsequently ponded with deionized (DW), canal irrigation (CW), and gypsum-saturated (GW) waters. The susceptibility to aggregate slaking was determined by comparing the IR measured in pre-saturated (slow wetting from below) and air-dry (fast wetting) soil columns ponded with CW. The FIRs of most soils decreased in the order GW>CW>DW. Seven soils were susceptible to clay dispersion induced by DW. Five soils were susceptible to clay dispersion induced by CW. Only two soils were susceptible to slaking. The fast wetting in these soils completely sealed the soil surface, reducing their IRs to zero from the start of leaching. Clay dispersion rather than aggregate slaking was the principal process inducing sealing and decreasing IR in these soils when subject to low-salinity waters. The indices WSA (water stable aggregates), MDC (mechanically dispersed clay) and MWDstir (mean weight diameter of stirring aggregates after a prewetting treatment) gave consistent and significant relationships with FIRs.