Sprinkler and surface irrigation effects on return flow water quality and quantity

A major conservation practice in the Upper Snake-Rock (USR) watershed is the conversion from furrow irrigation to sprinkler irrigation. We compared the effect of irrigation system type on water quality and quantity at the watershed scale. Six small watersheds (150-700 ha) were identified with 5 to 70% of the cropland sprinkler irrigated and the remaining fields surface or furrow irrigated. Other agricultural land uses, cropping practices and soils were similar among watersheds. Water quality and quantity entering and exiting each watershed were measured with automated samplers during the irrigation season. Irrigation inflow to watersheds and outflow from watersheds did not decrease as sprinkler irrigated area increased. This probably results from the flow rate allocation system used on the Twin Falls irrigation tract. Annual sediment loss (r=-0.19, P=0.40) and concentration (r=-0.38, P=0.30) also did not correlate with the relative amount of sprinkler irrigated area. Annual sediment loss (r-0.87, P=0.03) and concentration (r-0.84, P=0.05) correlated with irrigation inflow—the more irrigation water delivered to a watershed the greater the outflow sediment concentration and loss. These preliminary results indicate that irrigation water delivery should be managed in addition to converting to sprinkler irrigation to improve water quality in this irrigated watershed