Soil C sequestration and CO₂ fluxes under maize-based Conservation Agriculture systems in the Eastern Cape, South Africa

Abstract

Traditional farming methods deplete soil carbon and contribute to carbon dioxide (CO₂) emissions. We investigated the effects of Conservation Agriculture principles on C sequestration and CO₂ flux from two agroecological regions in the Eastern Cape province, South Africa, over five cropping seasons in the period 2012–2015. The field trials were laid in a split–split plot design. The main treatments were the tillage system, as conventional tillage or no-till. The sub-treatments were the crop rotation pattern: maize–fallow–maize (MFM); maize–fallow–soybean (MFS); maize– wheat–maize (MWM); or maize–wheat–soybean (MWS). Residue management after each crop in rotation was residue removal (R^–) or residue retention (R⁺). The biomass and C-inputs by the crop rotations were both in the order: MWM > MWS > MFM > MFS. R⁺ resulted in greater levels of particulate organic matter (POM) than R^–. The former was the only factor to significantly (p < 0.05) increase soil organic carbon (SOC) in the 0–5 cm depth layer at both sites after two years. CO₂ flux under conventional tillage was 20% higher than with no-till. The CO₂ fluxes were significantly influenced by air temperature (p < 0.001, r ² = 0.41) and soil bulk density (p < 0.001, r ² = 0.16). The results suggest that MWM or MWS crop rotation in conjunction with R⁺ under no-till offer the greatest potential for biomass and C-inputs, and consequently C sequestration, in sub-humid and semi-arid agroecological regions of South Africa.