FURROW IRRIGATION WATER-QUALITY EFFECTS ON SOIL LOSS AND INFILTRATION

Irrigation-induced erosion Is a serious problem in the western USA whe re irrigation water quality can vary seasonally and geographically. We hypothesized that source-water electrical conductivity (EC) and sodiu m adsorption ratio (SAR = Na/[(Ca + Mg)/2](0.5), where concentrations are in millimoles of charge per liter) affect infiltration and sedimen t losses from irrigated furrows, and warrant specific consideration in irrigation-induced erosion models. On a fallow Portneuf silt loam (co arse-silty, mixed, mesic Durixerollic Calciorthid), tail-water sedimen t loss was measured from trafficked and nontrafficked furrows irrigate d with waters of differing quality. Treatments were the four combinati ons of low or high EC (0.6 and 2 dS m(-1)) and low or high SAR (0.7 an d 12 [mmol(c) L(-1)](0.5)). Slope is 1%. Twelve irrigations were monit ored. Each furrow received two irrigations. Main effects for water qua lity, traffic, and first vs. second irrigations were significant for t otal soil loss, mean sediment concentration, total outflow, net infilt ration, and advance time. Average tail-water soil losses were 2.5 Mg h a(-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 se diment concentration from 6.2 to 8.7 g L(-1). Net infiltration decreas ed 14% in high SAR compared with low SAR treatments. Soil loss increas ed 68% for second irrigations, and net infiltration fell 23% in traffi cked furrows, but water-quality effects were the same. Water quality s ignificantly influenced infiltration and erosion processes in irrigate d furrows on Portneuf soils.