Carbon Dioxide Fluxes and Carbon Stocks under Conservation Agricultural Practices in South Africa

Understanding the impacts of agricultural practices on carbon stocks and CO 2 emission is imperative in order to recommend low emission strategies. The objective of this study was to investigate the effects of tillage, crop rotation, and residue management on soil CO 2 fluxes, carbon stock, soil temperature, and moisture in the semi-arid conditions in the Eastern Cape of South Africa. The field trial was laid out as a split-split-plot design replicated three times. The main plots were tillage viz conventional tillage (CT) and no-till (NT). The sub-plots were allocated to crop rotations viz maize–fallow–maize (MFM), maize–oat–maize (MOM), and maize–vetch–maize (MVM). Crop residue management was in the sub-sub plots, viz retention (R+), removal (R−), and biochar (B). There were no significant interactions ( p > 0.05) with respect to the cumulative CO 2 fluxes, soil moisture, and soil temperature. Crop residue retention significantly increased the soil moisture content relative to residue removal, but was not different to biochar application. Soil tilling increased the CO 2 fluxes by approximately 26.3% relative to the NT. The carbon dioxide fluxes were significantly lower in R− (2.04 µmoL m −2 s −1 ) relative to the R+ (2.32 µmoL m −2 s −1) and B treatments (2.36 µmoL m −2 s −1 ). The carbon dioxide fluxes were higher in the summer (October–February) months compared to the winter period (May–July), irrespective of treatment factors. No tillage had a significantly higher carbon stock at the 0-5 cm depth relative to CT. Amending the soils with biochar resulted in significantly lower total carbon stock relative to both R+ and R−. The results of the study show that NT can potentially reduce CO2 fluxes. In the short term, amending soils with biochar did not reduce the CO 2 fluxes compared to R+, however the soil moisture increases were comparable.