Th e effi cacy of polyacrylamide to reduce nutrient movement from an irrigated fi eld

ABSTRACT. Irrigation-induced erosion contributes to elevated sediment and nutrient concentrations in irrigation return-flow water. Polyacrylamide (PAM) is an effective flocculent widely used to reduced soil erosion. We hypothesized PAM would reduce transport of sediment and nutrients in surface irrigation water flowing over soil. We measured nutrients in irrigation inflow and runoff water and total and extractable nutrients in sediment transported from agricultural fields. Treatments were: (1) PAM application and no PAM (control), (2) three flow rates (7.5, 15.0, and 22.5 L min- 1), (3) distance along the furrow (1 m below the inflow point and 40 m down furrow), and (4) time during irrigation (0.5, 3.5, and 6.5 h after initial inflow). After irrigation water flowed 40 m, water flowing in furrows receiving PAM treatments reduced the NO3-concentration in runoff by 85 % and the total P concentration in water by 90 % compared to runoff water in furrows without PAM, regardless of flow rate. Mass export of NH4 +, NO3-, dissolved reactive phosphorus (DRP), total P, K, Ca, Mg, Fe, Mn, Cu, B, and Zn in untreated irrigation runoff water increased as the flow rate increased from 7.5 to 22.5 L min- 1. Export of these nutrients, via sediment carried by untreated irrigation runoff water, increased from 2 to 5 fold as the flow rate increased from 7.5 to 22.5 L min-1. After water flowed 40 m, transport of these extractable nutrients was reduced from 10 to 40 fold in PAM-treated furrows. With proper application, PAM reduces nutrient loss from furrow-irrigated agricultural fields, protecting surface water and groundwater quality