Topsoil removal and cultivation effects on structural and hydraulic properties

Topsoil removal and intensive cultivation of fragile sandy loam soil may reduce water movement into and within the soil and decrease available water capacity. The purpose of this study was to determine if topsoil removal (SSR) and 10-year cultivation have adverse effects on the structural and soil water retention properties. The study was conducted on a fine sandy loam soil in humid tropical coastal plain soils in southern Nigeria. We measured particle size, soil organic matter, pore size through water desorption analysis and infiltration and related water retention properties. Results showed that topsoil removal and cultivation resulted in significant reduction in infiltration, saturated hydraulic conductivity and available water contents and increased the bulk density. Topsoil removal increased fine particle-size fractions and created a shift in pore size distribution to a greater micro porosity. Soil water storage in terms of useful available water (UAW) and easily available water (EAW) were significantly low (p < 0.05) in SSR, reaching 62% reduction. Top soil removal and cultivation resulted in 67% and 32% decreased OM respectively. Loss of OM leading to low water retention at 10 kPa and 1500 kPa indicates a high risk of water stress and quicker soil drying even after heavy rainfall. Loss of organic matter and silt+clay fraction were the major drivers of changes in UAW and EAW in SSR soils. The results of this study confirmed that many structural and water retention characteristics are altered by cultivation and topsoil removal, and are useful in defining the physical quality response indices of fine sandy loam soils.