Impacts of rock fragment cover, polyacrylamide and manure with lime on soil moisture, surface runoff, and soil loss

This study investigates the impacts of rock fragment cover (RFC) and soil amendments (polyacrylamide (PAM) + lime (L) and Manure + Lime), individually and in combination, on soil moisture, surface runoff and soil loss. Worldwide, the effects of different RFCs on soil erosion are properly evaluated. However, there are few published studies on the effects of soil amendments on soil erosion and the synergistic effects of RFC and amendments. Particularly in the highlands of Ethiopia, little study is known about how PAM + L influences soil erosion and has not investigated the Manure + L, and the individual and combined impacts of RFC with amendments. Simulated rainfall was used to investigate how different combinations of RFC (completely removal (0%), 16%, 46%, 62%) and soil amendments (0, 0.4 t/ha PAM + 2 t/ha lime, 5 t/ha manure + 2 t/ha lime) affect soil moisture and soil erosion in three replications at 15 and 23% slopes. Soil moisture content (SMC) and time to runoff (TRO) increased as RFC increased while runoff and soil loss decreased at both slopes. RFC with 46% and 62% combined with PAM + L and Manure + L significantly (p < 0.05) increased the SMC and decreased runoff and soil loss. Surface RFC of 16%, 46% and 62 % reduced soil loss by 38%, 67% and 69% relative to 0% RFC or control, respectively. Soil loss reduction was found between 73-87% and 57-67% under the plot of PAM + L combined with increasing RFC from 16, 46 and 62% at 15 and 23% slopes, respectively, compared to control. The effects on SMC improvement and erosion reduction were insignificant, between 46 and 62%. Application of PAM + L alone is more effective in soil loss reduction than Manure + L. PAM + L reduced soil loss by 72% and 57% and improved SMC by 15% and 14% at 15 and 23% slopes, respectively. Thus, mulching or leaving the presence of 46% surface RFC and the addition of PAM + L were recommended for SMC improvement and erosion reduction. The findings might contribute to exploring alternative soil and water conservation strategies via avoiding the entire removal of RFC rather than using it in combination with soil amendment.