Abstract
BackgroundTillage practices greatly affect carbon (C) stocks in agricultural soils. Quantification of the impacts of tillage on C stocks at a regional scale has been challenging because of the spatial heterogeneity of soil, climate, and management conditions. We evaluated the effects of tillage management on the dynamics of soil organic carbon (SOC) in croplands of the Northwest Great Plains ecoregion of the United States using the General Ensemble biogeochemical Modeling System (GEMS). Tillage management scenarios included actual tillage management (ATM), conventional tillage (CT), and no-till (NT).ResultsModel simulations show that the average amount of C (kg C ha-1yr-1) released from croplands between 1972 and 2000 was 246 with ATM, 261 with CT, and 210 with NT. The reduction in the rate of C emissions with conversion of CT to NT at the ecoregion scale is much smaller than those reported at plot scale and simulated for other regions. Results indicate that the response of SOC to tillage practices depends significantly on baseline SOC levels: the conversion of CT to NT had less influence on SOC stocks in soils having lower baseline SOC levels but would lead to higher potentials to mitigate C release from soils having higher baseline SOC levels.ConclusionFor assessing the potential of agricultural soils to mitigate C emissions with conservation tillage practices, it is critical to consider both the crop rotations being used at a local scale and the composition of all cropping systems at a regional scale.
Highlights
Tillage practices greatly affect carbon (C) stocks in agricultural soils
It is estimated that conservation tillage practices across the United States may drive large-scale sequestration on the order of 24–40 Tg C yr-1 (Tg: teragram; 1 Tg = 1012 g), and that additional C sequestration of 25–63 Tg C yr-1 can be achieved through other modifications to traditional agricultural practices
Croplands and tillage management history Major historical changes in land use/land cover within the ecoregion were directly related to conversions between cropland and grassland
Summary
Tillage practices greatly affect carbon (C) stocks in agricultural soils. Quantification of the impacts of tillage on C stocks at a regional scale has been challenging because of the spatial heterogeneity of soil, climate, and management conditions. In regard to the C credit scenario established by the Kyoto Protocol, it is widely suggested that conversion of conventional tillage (CT) to no-till (NT) can help to support the profitability of C credits for farmers The uncertainties of these sequestration scenarios, depend on soil organic carbon (SOC) monitoring and/or models [2]. Based on the assessment of NEE over six years, Hollinger et al [2] estimated C stocks for corn/soybean rotation ecosystems in the North Central Region of the United States, and observed a C sink under NT at the local scale which, is not necessarily true on a regional scale They attributed this discrepancy to regional consumption of grain combined with C emissions associated with agricultural practices
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