Furrow irrigation water-quality effects on soil loss and infiltration

Irrigation-induced erosion Is a serious problem in the western USA where irrigation water quality can vary seasonally and geographically. We hypothesized that source-water electrical conductivity (EC) and sodium adsorption ratio (SAR = Na/[(Ca + Mg)/2](0.5), where concentrations are in millimoles of charge per liter) affect infiltration and sediment losses from irrigated furrows, and warrant specific consideration in irrigation-induced erosion models. On a fallow Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid), tail-water sediment loss was measured from trafficked and nontrafficked furrows irrigated with waters of differing quality. Treatments were the four combinations of low or high EC (0.6 and 2 dS m(-1)) and low or high SAR (0.7 and 12 [mmol(c) L(-1)](0.5)). Slope is 1%. Twelve irrigations were monitored. Each furrow received two irrigations. Main effects for water quality, traffic, and first vs. second irrigations were significant for total soil loss, mean sediment concentration, total outflow, net infiltration, and advance time. Average tail-water soil losses were 2.5 Mg ha(-1) from low EC/low SAR furrows, 4.5 Mg ha(-1) from low EC/high SAR furrows, 3.0 Mg ha(-1) from high EC/high SAR furrows; and 1.8 Mg ha(-1) from high EC/low SAR furrows. Elevating water EC decreased sediment concentration from 6.2 to 4.6 g L(-1), but increasing SAR increased sediment concentration from 6.2 to 8.7 g L(-1). Net infiltration decreased 14% in high SAR compared with low SAR treatments. Soil loss increased 68% for second irrigations, and net infiltration fell 23% in trafficked furrows, but water-quality effects were the same. Water quality significantly influenced infiltration and erosion processes in irrigated furrows on Portneuf soils.