Long-term conservation agriculture effects on soil erosion and runoff in Eastern Cape, South Africa

Abstract Purpose Soil erosion by water is strongly influenced by agronomic management practices on arable agricultural land. However, conservation agriculture (CA) has the potential to reduce soil loss through erosion by minimizing surface runoff. The objective of the study was to investigate the effects of tillage, crop rotation and crop residue management practices on soil loss and runoff after a decade of CA implementation. It was hypothesized that adoption of conservation agricultural practices significantly reduces soil loss and runoff. Materials and methods The experiment was structured in a split split-plot trial layout with 16 treatment combinations that are replicated in 3 blocks. The main treatments, sub treatments and sub-sub treatments were allocated to tillage [no-tillage (NT) and conventional tillage (CT)], crop rotations [maize-fallow-maize (MFM); maize-fallow-soybean (MFS); maize-wheat-maize (MWM); maize-wheat-soybean (MWS)], and crop residue management system [residue retention (R+) and residue removal (R-)], respectively. A rainfall simulator was used to generate a standardized rain-shower on a plot with standard surface area, the amount of runoff was collected and measured, solid sediments washed were obtained through drying and weighing. The data were subjected to Analysis of Variance and Principal Component Analysis while multiple regressions were used to assess the impact measured soil parameters on soil loss and runoff. Results and Discussion Results showed that NT reduced soil loss and runoff by 40% and 2.25% respectively, compared to CT. In terms of crop rotation, the highest runoff and soil loss were observed under MFM and lowest under MWS. Likewise, residue retention reduced soil loss by 22% and runoff by 4.38% in contrast to R-. Low soil loss and runoff were attributed to improved porosity and aggregation in plots under CA practice. Runoff and soil loss were correlated with other soil physical properties and predicted using the developed regression models. Furthermore, soil loss could be predicted using multiple linear regression from bulk density and soil water content, runoff was estimated using bulk density and porosity. Conclusion This study ascertained the benefits of CA in improving soil resistance to hydric erosion while sustaining its quality over time. However, the need for further evaluation and validation of the developed erodibility model remains crucial. This research can contribute to the development of regionally tailored CA recommendations for maintaining soil quality, and ultimately, reducing soil degradation while enhancing agricultural productivity.