Effect of polyacrylamide on the erodibility factor of a loam soil

Despite the proven utility of the Universal Soil Loss Equation (USLE) to predict soil rainfall erosion, it has limited precision in predicting soil loss in some soil series. Also, runoff is a factor in rainfall erosion and some models, such as the modified USLE (USLE-M), include runoff in predicting soil erosion. The soil erodibility factor is an essential component in both models and this may be affected by application of soil conditioners, such as polyacrylamide (PAM). The objectives of this study were to determine the effects of different rates of PAM (0, 1, 2, 4, and 6 kg ha−1) applied with sprinkler irrigation water, followed by two sprinkler irrigations with no PAM, on the erodibility of a loam soil under a rainfall simulator in a laboratory. The range of erodibility factor Ku obtained by the USLE method was 0.0136–0.0585 t h MJ−1 mm−1 with the highest and lowest values for a 0 kg ha−1 PAM application rate and the third irrigation event and a 6 kg ha−1 PAM application rate and the first irrigation event, respectively. However, the range of the erodibility factor obtained by the modified USLE method Kum was 0.0324–0.0768 t h MJ−1 mm−1 with the highest and lowest values for a 0 kg ha−1 PAM application rate and the third irrigation event and a 6 kg ha−1 PAM application rate and the first irrigation event, respectively. On average, the values of Kum were 1.9 times those obtained by the USLE method. The value of the soil erodibility according to the USLE nomograph K for the soil used in this study is comparable to that obtained by the USLE method. However, the values of Kum were about 63% higher than the value of K obtained by the USLE nomograph. Since multiple applications of PAM increase application cost, the required PAM application rates are presented according to the number of irrigations used in the growing season.