No-Till Impact on Soil and Soil Organic Carbon Erosion under Crop Residue Scarcity in Africa

Although no-till (NT) is now practiced in many countries of the world, for most smallholders, the crop residues are of such a value that they cannot be left on the soil surfaces to promote soil protection, thus potentially limiting NT benefits and adoption. In this study our main objective was to evaluate runoff, soil, and soil organic carbon (SOC) losses from traditional small-scale maize (Zea mays) field under conventional tillage (T) and NT, with crop residues cover of less than 10% during the rainy season, in South Africa. Six runoff plots of 22.5 m(2) (2.25 x 10 m) under NT and T since 2002 were considered. At each plot, soil bulk density (rho(b)) and SOC content of the 0-0.02 m layer were estimated at nine pits. Top-soil SOC stocks were 26% higher under NT than under T (P = 0.001). The NT reduced soil losses by 68% (96.8 vs. 301.5 g m(-2) yr(-1), P = 0.001) and SOC losses by 52% (7.7 vs. 16.2 g C m(-2) yr(-1), P = 0.001), and differences in runoff were not significant. Dissolved organic carbon accounted for about 10% of total SOC losses and showed significantly higher concentrations under T than NT (1.49 versus 0.86 mg C m(-2) yr(-1)). The less erosion in NT compared to T was explained by a greater occurrence under NT of indurated crusts, less prone to soil losses. These results showed the potential of NT even with low crop residue cover (<10%) to significantly reduce soil and SOC losses by water under small-scale agriculture.