Interaction Effects of Polyacrylamide Application Rate, Molecular Weight, and Slope Gradient on Runoff and Soil Loss under Sprinkler Irrigation

Abstract

Runoff and soil loss affect both farmland productivity and environmental quality. This study tested the interaction effects among polyacrylamide (PAM) application rate, PAM molecular weight, and slope gradient on runoff and soil loss under simulated sprinkler irrigation in laboratory. Experimental treatments consisted of four PAM application rates of 0 (control), 0.5, 1.0, and 2.0 g m-2, two PAM molecular weights of 12 and 18 Mg mol-1, and three slope gradients of 5o, 15o, and 25o. Results indicated that compared with the control treatment, PAM application generally decreased total runoff volume but increased soil loss. Total runoff volume and soil loss increased with the increased PAM application rate. Under control treatment, total runoff volume increased with the increased slope gradient. However, total runoff volume was similar for different slope gradients when PAM application rates were 0.5 and 1.0 g m-2, but it decreased with the increased slope gradient when PAM application rate was 2.0 g m-2. Total soil loss increased with the increase of slope gradient under experimental conditions. Polyacrylamide molecular weight did not affect total runoff volume but did soil loss significantly at P < 0.001, and a high PAM molecular weight resulted in less soil loss than a low one did. Statistical analysis demonstrated that there existed a significant interaction effect at P < 0.001 between PAM application rate and soil slope gradient on runoff volume and soil loss. The interaction effects between PAM molecular weight and slope gradient or among PAM application rate, PAM molecular weight, and slope gradient on soil loss were also significant at P < 0.01. A PAM application rate less than 2 g m-2 is suggested to control water and soil loss on sloped lands under sprinkler irrigation.