Integration effect of vetiver grass strips with maize population density on soil erosion under two contrasting slopes of rainforest agroecology

Abstract

Water erosion is a global concern that threatens sustainable agriculture. Using vetiver grass strip (VGS) and maize population density (MPD) separately to control soil erosion has been documented. Complementing VGS with high MPD could enhance crop yield and erosion control efficiency on sloping lands but there is no quantitative study on the combined effects of VGS with MPD on soil nutrient erosion globally. Thus, a 2-year field experiment was conducted to assess the effectiveness of VGS + MPD in controlling soil nutrient erosion and improving maize yields on two contrasting slopes under rainforest agroecology. Five treatments [VGS established at 5 m intervals with MPD of 40,000 stands ha−1 (VGS5 + MPD40); VGS established at 5 m intervals with MPD of 53,333 stands ha−1 (VGS5 + MPD53); VGS established at 10 intervals with MPD of 40,000 stands ha−1 (VGS10 + MPD40); VGS established at 10 intervals with MPD of 53,333 stands ha−1 (VGS10 + MPD53) and plot planted to MPD of 53,333 stands ha−1 only serves as control (MPD53)] were imposed on 5 % and 10 % slopes. Runoff was higher in control (MPD53) than other treatments by a range of 92.2 % to 73.8 % on a 5 % slope and 73.3 % to 52.2 % on a 10 % slope. Similarly, the relative reductions in soil loss compared to the control ranged from 89.9 % to 70.2 % on a 5 % slope and 90.8 % to 84.2 % on a 10 % slope. Amongst treatments, VGS5 + MPD53 had the lowest nutrient volume discharge on both slopes due to complimentary impacts of higher MPD to provide a full vegetation cover to prevent splash erosion while closely spaced VGS helps to trap transportable fine particles down the slope. Runoff and soil loss from the 10 % slope exceeded the 5 % slope by 61.2 % and 77.4 % respectively. Average maize yields for VGS5 + MPD53 on both slopes were significantly (p ≤ 0.05) higher than other treatments and maize yield on the 5 % slope exceeded the 10 % slope by 30.9 %. Slope gradient is a major driving force for water erosion and integration of VGS5 with MPD53 is the most effective in controlling soil nutrient erosion and improving maize yield on 5–10 % slopes under rainforest agroecology.