REDUCTIONS IN HYDRAULIC CONDUCTIVITY AND INFILTRATION-RATE IN RELATION TO AGGREGATE STABILITY AND IRRIGATION WATER TURBIDITY

Arid and semiarid soils are characterized by reductions in hydraulic c onductivity (HC) and infiltration rate (IR) when employing low salinit y/sodicity waters. Such reductions are further exacerbated when irriga ting 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 kaoli nite). When conducting field measurements of IR or permeating duplicat e columns of 1:1 soil:sand mixtures with solution series of decreasing concentration (50 to 0 mol(c) m(-3)) at any of the above SAR levels, IR and HC decreased with decreasing electrolyte concentration. Substan tial losses in IR and HC ( approximate to 40-60%) were observed when p ermeating solutions with electrolyte concentration equal to or higher than the respective CCC of the soil-clay. However, IR and HC dropped t o approximately 15-20% of their respective maximum values with the per meation of turbid runoff water (0.07% fine clay) adjusted to electroly te 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, respecti vely). Such reductions were larger than the corresponding reductions i n HC and IR when permeating clear solutions of equivalent SAR and elec trolyte concentration (Delta HC approximate to 50-60% and Delta IR = 5 1 +/- 3%). This result indicated the ability of suspended fine clay pa rticles in the permeating water to flocculate in the soil conducting p ores causing their clogging.