Assessing nutrient losses with soil erosion under different tillage systems and their implications on water quality

An increased public perception of the role of agriculture in non-point source pollution has stimulated the need for information on the effect of conventional and sustainable agricultural management systems on water quality. While information on run-off and soil erosion is readily available in Zimbabwe, there is dearth of knowledge on the relative losses of nutrients as a result of soil erosion and their effect on water quality. This study sought to quantify the amount of nutrients lost as a result of soil erosion and thus enable conclusions to be drawn on the implications on water quality. Research work was carried out in the semi-arid region of Zimbabwe under granite-derived, inherently infertile sandy soils. Soil erosion was quantified under three tillage systems conventional tillage (CT); mulch ripping (MR); tied ridging (TR) over three years. Run-off and sediments were analysed for N, P and K. The results showed that N and K losses were significantly higher ( p < 0.001) under CT (15.8 and 34.5 kg ha −1 yr −1, respectively) compared to the MR (2.3 and 0.6 kg ha −1 yr −1, respectively) and TR (2.7 and 4.3 kg ha −1 yr −1, respectively). Due to the immobility of P and its small quantities in these soils, P losses were also low across all treatments (