2007 Annual Report 1a.Objectives (from AD-416) 1. Identify the effect of converting surface irrigation to overhead irrigation on selected water quality parameters at the irrigated field, drainage, and watershed/tract scale. 2. Calibrate and validate watershed assessment model(s) for irrigated tracts. 3. Determine the most effective placement of the overhead irrigation systems. 1b.Approach (from AD-416) We propose to measure the water flow, suspended sediment, and total and dissolved phosphorus in selected individual irrigation return flow surface drains during the irrigation season. The individual surface drains are spatially and hydrologically isolated and can serve as sub-basins or smaller watersheds (similar to HUC 10 or 12). This data will be related to the crops and cropping practices, animal waste applications, and distribution of irrigation systems within each of the drainage areas. Some information will be estimated from current aerial imagery and agency databases, as well as from field surveys. This information will be used to determine the relative effect of irrigation system on return flow water quality parameters, and to validate watershed assessment models for irrigated tracts. The models may then be used to identify the most beneficial placement of overhead irrigation systems in the tract, as well as the effect of other conservation practices on water quality and quantity. Documents reimbursable with NRCS. Log 27436. Formerly 5368-12130-009-02R (6/07). 3.Progress Report This report documents research conducted under a Reimbursable Agreement between ARS and the Idaho Natural Resource Conservation Service (NRCS), Boise, Idaho. This project is one of eight special emphasis watersheds funded by NRCS for the Conservation Effects Assessment Project (CEAP). The major emphasis is determining the effects of conservation practices in an irrigated agriculture watershed. Additional details of research can be found in the report for the parent project CRIS 5368-13000-007-00D, Improved Water Resources Management for Irrigated Agriculture in the Pacific Northwest. The overall objectives of this project are to evaluate changes from 1970 in water and salt balances for a 200,000 acre irrigated tract, and determine the effects of converting from surface irrigation to sprinkler irrigation on return flow water quality in six small watersheds (400 to 1900 acres) within the irrigated tract. Field sampling will measure suspended sediment, total and soluble nutrients, and water flow rates for irrigation inflows and outflows from the irrigation tract and each small watershed. These data will be related to land use, management practices and irrigation system type. Water quality monitoring was initiated at 23 return flow sites in January 2005 and at six small watersheds when the irrigation season started in April 2005. Preliminary results indicate that sediment loss from the irrigation tract in 2005 was about one-fourth of what it was in 1970. These results also indicate that the irrigation tract now has a net gain of soluble salts rather than a net loss. Much of these changes can be attributed to increasing the amount of sprinkler irrigated land from less than 10% in 1970 to almost 40% in 2005. Data collection tentatively will continue through the 2008 irrigation season. Project coordination with Idaho NRCS occurs primarily through an annual stakeholder meeting and periodic telephone calls.