Response of soil properties and maize yield to simulated erosion by artificial topsoil removal

The study was aimed at identifying the soil properties responsible for maize yield decline on eroded soils and at quantifying their relationship with yield. Topsoil was artificially removed to incremental depths of 0, 5, 10, 15 and 20 cm to simulate various degrees of erosion. Maize growth and yield were monitored on the plots and soil physical and chemical properties were determined after two years (4 seasons) of cultivation. Soil pH was significantly higher on the control plot and decreased with increased depth of topsoil removal. Bulk density (BD) increased with depth of topsoil removal from a mean value of 1.38 g cm(-3) under control to 1.55 g cm(-3) at 20 cm depth of removal, while cone index of penetrometer resistance (CI) correspondingly increased from 1.09 g cm(-2) to 1.37 g cm(-2). Maize yield significantly decreased in the first year from 3.2 t ha(-1) on the control plot to 0.12 t ha(-1) where 20 cm of topsoil was removed and correspondingly from 1.85 to 0.09 t ha(-1) in the second year of cropping. Maize yield decreased exponentially with increase in depth of topsoil removal (r(2)=0.99, P < 0.01) with an average of 55% yield loss on the removal of just 5 cm topsoil. Soil organic carbon (SOC), BD, CI, field capacity (FC), pH and exchangeable Mg2+ were significantly correlated to maize yield parameters. However, factor analysis showed that the combination of SOC and exchangeable Mg2+ with soil physical properties (BD, FC, CI and depth of topsoil removal) explained 99% of variation in maize grain yield. The need for conservation farm practices is recommended on the soil to prevent soil degradation.