Polyacrylamide for surface irrigation to increase nutrient-use efficiency and protect water quality

Furrow irrigation systems have a greater application capacity, are less cos tly, and use less energy than sprinkler systems but furrow irrigation produ ces greater runoff, erosion, and deep percolation losses. Phosphorus (P) an d nitrogen (N) losses are associated with runoff sediment, and can be minim ized by eliminating irrigation-induced erosion. Excessive leaching of inorg anic and organic solutes commonly occurs at the inflow region of furrow irr igated fields where infiltration opportunity times are longer. In one conse rvation practice, a high molecular weight, anionic polyacrylamide (PAM) is applied to advancing furrow stream flows at a concentration of 10 mg L-1. B ecause PAM stabilizes furrow soil and flocculates suspended sediment, we hy pothesized that this treatment would reduce runoff losses of sediment, moly bdate reactive P (MRP), total P, NO3-N, and chemical oxygen demand (COD). P olyacrylamide treatment may increase furrow infiltration in some soils. How ever, we hypothesized that because it permits higher initial inflows, PAM w ould not increase NO3-N or Cl leaching relafive to conventional, constant i nflow irrigation. To test the first hypothesis, all treatments had the same inflow regime. For hypothesis two, control inflows were a constant 15 L mi n(-1); PAM treated inflows were cut back from 45 to 15 L min(-1) after furr ow advance. Irrigation runoff and percolation waters were sampled and analy zed. Polyacrylamide increased infiltration and decreased runoff, particular ly early in the irrigations. Mean cumulative runoff sediment loss over 12 h was 11.86 kg for each control furrow vs 1.15 kg for PAM-treated furrows. T he PAM reduced 12-h cumulative sediment losses in runoff by 90%, MRP by 87% , total P by 92%, and COD by 85%, relative to control furrows. Polyacrylami de had no field-wide, season-long effect on cumulative amounts of water, NO 3-N or Cl leached. The PAM-technology effectively prevented soil nutrient l osses, increased nutrient-use efficiency, and decreased N and P loads in ir rigation return flows and receiving surface waters.