Tillage, crop rotation, residue management and biochar influence on soil chemical and biological properties

Soil and crop productivity cannot be maintained unless declining soil fertility is replenished. A three-year factorial experiment using a split-split-plot design, replicated three times, was used to evaluate the response of pH, electrical conductivity, exchangeable cations (Ca, Mg, K and Na), microbial biomass carbon, total nitrogen and total carbon to conservation agriculture in the Eastern Cape, South Africa. The whole plot factors were conservation tillage and no tillage, the sub-plot factors three crop rotation practices (i.e. maize → oat → maize; maize → vetch → maize and maize → fallow → maize) and the sub-sub-plot factors three residue management practices (viz. residue retention; residue removal and biochar amendment). Soil pH and EC were not affected (p > 0.05) by these agricultural practices after 3 years. Magnesium (p < 0.05) and potassium (p < 0.01) were significantly affected by tillage at 0–5 cm depth. The tillage x crop rotation x residue management interaction was only significant (p < 0.01) for MBC at a depth of 0–5 cm depth. Interactions of tillage x crop rotation (p < 0.001) and crop rotation x residue management (p < 0.0001) were also significant. After three years, conservation agriculture resulted in net increases in total carbon, total nitrogen and MBC concentrations compared to conventional agricultural practices.