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Water erosion-induced CO2 emissions from tilled and no-tilled soils and sediments

Chaplot, V., Mchunu, C.N., Manson, A., Lorentz, S., Jewitt, G.
Agriculture, ecosystems & environment 2012 v.159 pp. 62-69
aggregate stability, best management practices, carbon dioxide, climate change, conventional tillage, corn, crop residues, emissions, greenhouse gases, land management, losses from soil, sediments, soil aggregates, soil organic carbon, soil sampling, water erosion, wet season, South Africa
The acceleration of soil erosion by water in most regions of the world in response to the anthropogenic modification of landscapes is a serious threat to natural ecosystem functionalities because of the loss of invaluable constituents such as soil particles and organic carbon (OC). While soil OC erosion is likely to be a major component of the global C cycle, water erosion-induced CO₂ emissions remain uncertain. In this study, our main objective was to compare the release of CO₂ from eroded topsoils and from the sediments exported by diffuse erosion during an entire rainy season. Conventional tillage (CT) and no-tillage (NT) maize treatments were considered in an attempt to set up best management practices to mitigate gaseous OC losses from agricultural soils. The study was conducted in the KwaZulu-Natal province in South Africa, whereas in many other areas of the developing world, erosion is severe and crop residue scarcity is the main challenge. CO₂ emissions from undisturbed 0–0.02m soil samples collected within 2.25m×10m runoff plots and from exported sediments by water erosion, were evaluated continuously at the laboratory over a 140-day period and compared to soil OC stocks. NT significantly reduced CO₂ emissions from both soils and sediments. Overall NT, which exhibited a greater carbon density than CT (17.70 vs 13.19kgCm⁻³), reduced soil gaseous emissions by 4.4% (10.40 vs 10.88gCO₂-Cm⁻², P<0.05) but had a much greater impact on the release of CO₂ from eroded sediments (0.185 vs 0.778gCO₂-Cm⁻²), which corresponded to a 76.3% decrease. For CT, cumulative 141-day emissions were, 19% greater in sediments (0.048gCO₂-CgC⁻¹) compared to soils (0.040gCO₂-CgC⁻¹), while for NT, emissions were 33% lower in sediments (0.024gCO₂-CgC⁻¹) compared to soils (0.032gCO₂-CgC⁻¹), these differences being significant at P<0.05. The lower erosion-induced CO₂ emissions under NT could be explained by a high soil aggregate stability (mean weight diameter of 2.29±0.05mm for NT vs 1.59±0.07mm for CT, P<0.05) and the associated enhanced protection of SOC from the decomposers. These results on a land management control of water erosion-induced CO₂ emissions, might allow improving the impact of terrestrial ecosystems on greenhouse gases concentration in the atmosphere and associated climate change.