Field measurement of effects of individual and combined application of biochar and polyacrylamide on erosion variables in loess and marl soils.

Controlling soil erosion, especially in its initial stages, is greatly important in natural resources management. Consequently, the present research aimed to control splash and interrill erosion in two soil types (marl at Marzan-Abad and loess at Maraveh-Tapeh sites in northern Iran) using biochar (BC) and polyacrylamide (PAM). We established 0.5 × 0.5-m plots and applied BC (800 g·m-2), PAM (2 g·m-2), and BC + PAM (800 g·m-2 + 2 g·m-2) with control plots and three replications on a slope of ~25%. We used a rainfall simulator to achieve rainfall intensity of 50 mm·h-1 with 30-min duration in the experiments. Analysis of the results obtained from the variables of splash and interrill erosion during the rainfall-runoff process showed that the PAM significantly (p ≤ 0.05) increased all study variables of splash erosion. For interrill erosion, it reduced the variables of soil loss and sediment concentration. However, the difference was not significant (p > 0.05) compared to the control plot and runoff from the two treatment sites increased relative to that from the control plots. The plot treated with BC showed decreased runoff volume, runoff coefficient, and soil loss compared to the control plot at the Marzan-Abad site, but the differences were not statistically significant (p > 0.05). However, the plot in which loess soil was treated with BC at the Maraveh-Tapeh site exhibited considerably (p ≤ 0.05) increased runoff and soil loss compared to the control plot. The entire results verified a wide range for benefit reduction of study treatments from +25.09 to -37.49% for runoff and from +38.59 to -231% for soil loss with more effectiveness for Maraveh-Tapeh Loess soil as well as combined application of BC and PAM. These findings contribute to improved understanding of proper application of soil amendments to control runoff and soil loss in loam and loess soils.