Written for Presentation at Conservation Agriculture for Sustainable Wheat Production in Rotation with Cotton

Abstract: Furrow irrigation has been identified as one of the main sources of excess sediment in the Yakima River Basin. In turn, this source of water-quality degradation is thought to be one of the causes for declining salmon runs in the Yakima River. The Washington Department of Ecology has set a sediment limit for irrigation return flows of 25 NTUs (56 mg/l). Some irrigators are converting their rill irrigation systems to either sprinklers or drip irrigation at a cost of $750 to $2500 per hectare. Other furrow irrigators are applying Polyacrylamide (PAM) and successfully decreasing sediment loads from furrows by 80 to 90 percent. Unfortunately, this cleaner water often erodes sediment from the tailwater ditch causing elevated NTU levels still too high to be returned to irrigation district canals and drainage ditches. The focus of this research was on inexpensive methods to further reduce sediment and nutrient loads from furrow irrigation by using PAM ($50/ha per year) with Surge irrigation ($300/ha), tailwater drains ($185/ha), tailwater checks ($60/ha), and grass-lined tail ditches ($25/ha). During the 2001 growing season after monitoring 5 irrigation events on 2 fields, PAM with a grassed lined tailwater ditch was the only treatment to maintain suspended solids below the required 25 NTUs (56 mg/l). The treatments in order of best to worst water quality were PA