Soil Organic C Trends in US Agroecosystems (Invited)

Agricultural management influences carbon dynamics in soils by changing the amount of carbon inputs associated with the productivity of crops, as well as losses driven largely by decomposition of residues and soil organic matter. Weather patterns also influence carbon dynamics by modifying plant production and decomposition. The DAYCENT ecosystem model was used to simulate carbon dynamics in agricultural lands of the Mid-Continent region of the US from 1979 to 2007. Cropping patterns were simulated according to data from the USDA National Resources Inventory, tillage practices were based on the data from the Conservation Technology Information Center, while soils input data were derived from USDA SSURGO, and weather data from the North American Regional Reanalysis Product. Carbon trends were compared evaluating the relative differences among dominant agroecosystems. Overall, US agroecosystems had a net increase in soil organic C during this time period, estimated at 14 to 18 Tg C/yr, with the largest increases occurring in Mid-Continent region. Furthermore, the increases in soil organic C were largely associated with setting-aside cropland from production, agroecosystems that included hay in rotation with annual crops, and systems with reduced tillage intensity. The influence of weather patterns and interaction with management was also evaluated, but longer-term trends in precipitation and temperature had a less of an effect on carbon dynamics than management. This research provides a baseline of current carbon dynamics in US agroecosystems, which is needed to evaluate potentials for carbon sequestration in support of future policy and management decisions.