Reductions in hydraulic conductivity and infiltration rate in relation to aggregate stability and irrigation water turbidity

Abstract

Arid and semiarid soils are characterized by reductions in hydraulic conductivity (HC) and infiltration rate (IR) when employing low salinity/sodicity waters. Such reductions are further exacerbated when irrigating with turbid water. Critical salt coagulation concentrations (CCCs) were determined at constant SAR 5, 10, 15, or 20 for clay fractions of a semiarid surface sample of the Muaq'qar soil (fine, mixed thermic, Typic Calciorthid) and for turbid runoff rain water, containing clay particles, which was generated from the same area. The results showed similar values for both types of clay (predominated by mica and kaolinite). When conducting field measurements of IR or permeating duplicate columns of 1:1 soil: sand mixtures with solution series of decreasing concentration (50 to 0 mol, m −3) at any of the above SAR levels, IR and HC decreased with decreasing electrolyte concentration. Substantial losses in IR and HC ( ≈40–60%) were observed when permeating solutions with electrolyte concentration equal to or higher than the respective CCC of the soil-clay. However, IR and HC dropped to approximately 15–20% of their respective maximum values with the permeation of turbid runoff water (0.07% fine clay) adjusted to electrolyte concentration slightly lower than the corresponding CCC of the soil-clay (5, 10, 15, or 20 mol c m −3 at SAR 5, 10, 15, or 20, respectively). Such reductions were larger than the corresponding reductions in HC and IR when permeating clear solutions of equivalent SAR and electrolyte concentration (ΔHC ≈ 50–60% and ΔIR = 51 ± 3%). This result indicated the ability of suspended fine clay particles in the permeating water to flocculate in the soil conducting pores causing their clogging.