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

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.