SEDIMENT POND EFFECTIVENESS FOR REMOVING PHOSPHORUS FROM PAM-TREATED IRRIGATION FURROWS

Abstract

Polyacrylamide (PAM) greatly reduces erosion on furrow-irrigated fields and sediment ponds can be constructedto remove suspended sediment from irrigation runoff. Both practices are approved for reducing phosphorus (P) loading inthe Lower Boise River Pollution Trading Project in southwest Idaho, but information is not available about using bothpractices on the same field. The objective of this study was to measure the combined effects of PAM application and sedimentponds on sediment and P losses from a furrow-irrigated field. Small sediment ponds (5.8 m2) with a 60-min design retentiontime were installed on two fields to receive runoff from PAM-treated or control furrows. Pond inflow and outflow weremonitored during a total of 11 irrigations on the two fields. Three crop years of data showed that applying PAM to furrowsreduced sediment and total P mass transport to the ponds 50% to 80%, which reduced the mass of sediment and total P retainedin the ponds. However, PAM application did not change the percentage of sediment (86%) and total P (66%) retained. ThePAM-sediment pond combination reduced average total P loss by 86% to 98%, based on the difference between untreatedinflow and PAM-treated outflow. PAM and sediment ponds had little or no effect on dissolved reactive P (DRP)concentrations. The mass of DRP retained in sediment ponds was directly related to the amount of water that infiltrated withinthe ponds. Applying PAM to irrigation furrows and installing sediment ponds at the end of the field can be an effectivecombination for reducing sediment and total phosphorus losses from furrow-irrigated fields, but these practices only reducedsoluble P losses by decreasing the volume of water that ran off the fields.