Erosion Control Effects of a Polymer-Based Soil Conditioner on Red Soil in Okinawa, Japan

Preventing soil degradation caused by water erosion is essential for sustainable agriculture and long-term agroecological development. The objective of this study was to evaluate the effectiveness of an ethylene-vinyl acetate (EVA) polymer-based soil conditioner in mitigating soil erosion, a key driver of soil degradation. Laboratory experiments and simulations employing the Water Erosion Prediction Project (WEPP) model were conducted to assess soil erodibility parameters and sediment yield of two soil types from Okinawa, Japan. A key contribution of this work is the integration of these experimentally determined erodibility parameters into the WEPP model for robust validation. Interrill and rill erosion processes were analyzed under different soil conditioner application rates. Laboratory results showed that applying the soil conditioner reduced interrill erodibility by 59 to 99% and rill erodibility by 65 to 100%, while increasing critical shear stress and water infiltration rate. The effectiveness varied between the two soil types due to differences in particle-size distribution and inherent erodibility. The soil conditioner exhibited a more pronounced impact on rill erosion. WEPP simulations confirmed sediment yield reductions of 73% to 99%, primarily influenced by changes in rill erodibility and critical shear stress. While its practical application will be subject to various field conditions, our findings confirm the significant potential of this soil conditioner as a strategy for preserving topsoil resources.