Soil hydraulic conductivity affected by slight saline water irrigation in North China

Abstract: The area irrigated with slight saline groundwater increases in North China because of fresh water shortage. The effects of salt concentration and sodium adsorption ratio (SAR) in irrigation water on saturated hydraulic conductivity of nonsodic (exchangeable sodium percentage ESP?0) and sodic (ESP?30) soils in North China were studied by soil column experiments in laboratory. The designed salt concentrations in irrigation water were 2.5, 10, and 25 mmolc/L, and its SARs were 0, 10, and 30 (mmolc/L)0.5, respectively. Irrigation with distilled water (salt concentration?0) also was conducted as a control treatment. The experiments included 2 soil sodicity levels, 9 irrigation water qualities, and one distilled water treatment, and total experimental treatments were 20. Experimental results demonstrated that saturated hydraulic conductivities of nonsodic soil on surface layers were significantly bigger than those on lower soil layers, in which they were similar to each other, under slight saline water leaching. Saturated hydraulic conductivities of sodic soil at various depths were closely related to salt concentration and SAR level in leaching water. The saturated hydraulic conductivities at various soil depths were small (0.04-0.10 cm/h) when sodic soil was leached with SAR of 30 (mmolc/L)0.5 and salt concentration of 2.5 mmolc/L, however they were significantly increased (0.8-2.5 cm/h) when salt concentration in leaching water increased to 25 mmolc/L at the same SAR level. Meanwhile, the saturated hydraulic conductivities on upper soil layers were significantly bigger that those on lower layers. The results indicated that the response mechanism and degree of nonsodic soil to slight saline water irrigation were different, and the dispersion degree of nonsodic soil was bigger than that of sodic soil under same irrigation water quality. When the degree of clay dispersion was weak, saturated hydraulic conductivities on upper soil layers were significantly greater than those on lower layers. When salt concentration in leaching water was 25 mmolc/L, averaged saturated hydraulic conductivity of nonsodic soil significantly decreased with the increase of SAR level in leaching water, but the variation tendency did not exist when salt concentrations were 2.5 and 10 mmolc/L. Average saturated hydraulic conductivity of sodic soil decreased with the increased SAR level or decreased salt concentration in leaching water, but it was not obviously affected by salt concentration when SAR level in leaching water was 0. Generally, the variation extent of averaged saturated hydraulic conductivity of nonsodic soil over the whole soil columns was 0.75-13.25 cm/h, and that of sodic soil was 0.06-6.50 cm/h under all tested water qualities. Steady saturated hydraulic conductivity of sodic soil increased with the increased salt concentration or/and decreased SAR in leaching water, but that of nonsodic soil basically decreased with the increased salt concentration or/and decreased SAR in leaching water. This research result can provide references for arranging a reasonable irrigation scheme about slight saline groundwater on nonsodic and sodic soils.