An ASABE Meeting Presentation Paper Number: 131619770 Nutrient Losses from an Irrigated Watershed in Southern Idaho David L. Bjorneberg, James A. Ippolito, Anita Koehn USDA ARS, Northwest Irrigation and Soils Research Lab, 3793 N 3600 E, Kimberly, ID 83341 Written for presentation at the 2013 ASABE Annual International Meeting Sponsored by ASABE Kansas City, Missouri July 21 – 24, 2013 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 -1 in 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. Keywords. Irrigation, Sediment Loss, Phosphorus, Nitrate Introduction Irrigation is important for stable production of high quality food and fiber. Surface irrigation is used on about 85% of the 299 Mha of irrigated land in the world (ICID, 2013). In the United States, surface irrigation is only used on 39% of the 22 Mha of irrigated land as sprinkler irrigation has steadily increased from 2 Mha in 1969 to 12 Mha in 2008 (USDA NASS, 2013). Sprinkler irrigation allows farmers to apply water more precisely than surface irrigation and eliminates irrigation runoff that is often required with surface irrigation for uniform water The authors are solely responsible for the content of this meeting presentation. The presentation does not necessarily reflect the official position of the American Society of Agricultural and Biological Engineers (ASABE), and its printing and distribution does not constitute an endorsement of views which may be expressed. Meeting presentations are not subject to the formal peer review process by ASABE editorial committees; therefore, they are not to be presented as refereed publications. Citation of this work should state that it is from an ASABE meeting paper. EXAMPLE: Author’s Last Name, Initials. 2013. Title of Presentation. ASABE Paper No. ---. St. Joseph, Mich.: ASABE. For information about securing permission to reprint or reproduce a meeting presentation, please contact ASABE at rutter@asabe.org or 269-932-7004 (2950 Niles Road, St. Joseph, MI 49085-9659 USA).