Runoff, Sediment and Nutrient Loads From Polyacrylamide-Coated-Fertilizer Soil Treatments Under Simulated Rainfall.

Phosphorus (P) and Nitrogen (N) are yield limiting macronutrients commonly supplied via fertilizers to cropland. P and N applied in excess of crop requirements can be lost to surface and ground waters and have been implicated in significant environmental problems such as eutrophication and hypoxia. Recent advances in polyacrylamide (PAM) technology have shown promise in reducing the risks of N and P losses from soil to surface waters by stabilizing sediment, increasing infiltration and reducing erosion and possibly by modifying nutrient-soil interactions as well.  Column tests and sorption isotherm studies were conducted to determine the impact of polyacrylamide on N and P adsorption to a silt loam soil and simulated rainfall/runoff/erosion studies were conducted to test the effectiveness of PAM applied as a coating of gypsum or diammonium phosphate (DAP) at reducing DAP N and P losses through runoff, erosion and leachate. Results from column tests and sorption isotherms indicate that PAM has little direct impact on soil-P and soil-N chemistry in this system.  However, at 10% slope and 63.5 mm hr^-1 precipitation for 1 hr, all PAM treatments were effective at reducing sediment and sediment bound P loads regardless of whether PAM was added as a coating on gypsum or directly on the DAP. Gypsum coated with 11.4 kg ha^-1 PAM was most effective at reducing sediment and sediment P loads with 80 and 83 % reductions in sediment and sediment P compared to controls, respectively. At 36% only three treatments exhibited significant reductions in sediment and sediment P loads. Gypsum coated with 11.4 kg ha^-1 PAM supplied in addition to 136 kg ha^-1 DAP reduced sediment and sediment P loads 71 and 53 %, respectively.  Nitrogen losses were not reduced significantly. At these relatively low PAM application rates, high slopes and intense rainfall rates, PAM coated gypsum and DAP proved to be effective delivery methods for limiting soil and soil P losses.