Polyacrylamide Influence on Runoff and Sediment Detachment from a Silt Loam Soil

Alternative erosion control practices using polyacrylamide (PAM) have received increased attention. This study examines the effect of PAM applied to soil when rainfall intensity, rainfall kinetic energy (KE), and PAM applied all interact, influencing time to runoff (ROt), cumulative runoff (ROc), and cumulative soil detachment (Dc). This study evaluated the response of a silt loam soil to aqueous PAM rates of 0 (untreated control), 20, and 40 kg ha-1 when applied to an initially air-dried soil. A total of 0.5 L of reverse osmosis water was sprayed on all soil beds. Simulated rainfall using a gravity-fed rainfall simulator was applied from 13.8 and 0.8 m fall heights at application rates of 64, 96, and 128 mm h-1. Results show significant benefit, as evidenced by increased ROt and reduced ROc and Dc for 20 and 40 kg ha-1 PAM application levels. This was true for all rain rates and durations up to 75 min whether rainfall was at or less than terminal velocity. Polyacrylamide was less effective at increasing ROt as rain rate increased. There was no difference in ROt with 40 kg ha-1 PAM compared to 20 kg ha-1 PAM; thus, the greater PAM application rate would not be recommended for this purpose. The benefits of reduced ROc and Dc with PAM were always greater for lower KE-rain (29% lower KE) than for higher KE-rain at a given rainfall intensity. Although both PAM application levels reduced ROc, for high KE-rain, only application of 40 kg ha-1 was significantly less than the untreated soil. For low KE-rain, ROc was significantly less with either PAM application level. Results show that PAM alone has a limited effect for maintaining infiltration rate; therefore, it is likely that regions with fewer intense convective storms would receive greater benefit from an increased PAM application rate. The greatest benefit of PAM was in reduced Dc where justification can be made for using increased PAM rates for high KE-rain, as documented by significantly less Dc for 40 kg ha-1 PAM compared to 20 kg ha-1 PAM at rain rates of 96 and 128 mm h-1. Under these conditions, both PAM rates significantly reduced Dc compared to untreated soil. With low KE-rain, Dc was significantly less for 20 kg ha-1 PAM compared to the untreated control, but 40 kg ha-1 PAM did not significantly reduce Dc since soil loss was so small.