The Impact of Agricultural Land Cover Change on Soil Hydraulic Properties: Implications for Runoff Generation

Abstract

Infiltration and hydraulic conductivity (K) play a key role in streamflow generation and groundwater recharge. The impact of agriculture on soil infiltration and K has been widely investigated. While many studies show decreases in infiltration and K, others show an increase or no change in both parameters. These variations highlight the importance of conducting local scale investigations. We investigated the impact of agricultural development and land cover changes on infiltration and K. Unsaturated hydraulic conductivity (K_unsat) was measured at the soil surface during both dry and wet seasons, and saturated hydraulic conductivity (K_sat) was measured at 25, 45, and 65 cm below the surface. Our results show that there were no significant differences in K_unsat between perennial crop cover and natural forests; however, agroforests did have significantly higher K_unsat than natural forests, which was attributed to higher soil moisture. There were no significant differences in K_sat among the perennial crops, agroforests, and natural forests at the 45 and 65 cm depths; however, at 25 cm, natural forests had significantly higher K_sat, which was attributed to the higher soil organic matter and lower bulk density in natural forest. The study showed that the impacts of agriculture and land cover change on K_sat do not extend to deeper soil layers. We used 2 years of rainfall intensity data, observed K_unsat and K_sat, and HYDRUS-1D modelling to infer any changes to runoff. We show that footpaths and perennial crop cover may generate more surface runoff than natural forests. This study adds to the literature on agricultural impacts on infiltration and K. More importantly, it shows that differences in crop type, management practices, and topographic location all play an important role on infiltration and K, showing the need for local field-based studies.