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Nutrient Losses from an Irrigated Watershed in Southern Idaho

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131619770,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   David L Bjorneberg, James A Ippolito, Anita C Koehn
Keywords:   Irrigation Sediment Loss Phosphorus Nitrate

Abstract. Water, sediment and nutrients flowing into and out of the 82,000 ha Twin Falls, ID irrigation tract were measured from 2005 to 2008. Approximately 80% of the water flowing into the watershed was irrigation water diverted from the Snake River. About 40% of the watershed inflow returned to the Snake River. Much of this return flow was water from subsurface drain tiles and tunnels that drain shallow groundwater. Converting from furrow to sprinkler irrigation, improved irrigation management, and constructed sediment ponds have reduced sediment loss from 460 kg ha-1 in 1971 to <100 kg ha-1in 2005. In 2007 and 2008, more sediment and phosphorus entered the watershed than returned to the Snake River. Diverting irrigation water into the watershed removed 6300 Mg of sediment, 21 Mg of dissolved P, and 32 Mg of total P from the Snake River on average each year. However, the watershed contributed almost 900 Mg of nitrate-N annually to the Snake River. Conservation practices have effectively reduced sediment and phosphorus losses from the watershed, emphasis now must shift to reducing nitrate loss from the watershed.

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