DAYCENT Model Assessment of Land Use Change and Management on C and N Fluxes in the USA Great Plains

Land use changes have dramatically altered the biogeochemical cycling associated with greenhouse gas (GHG) fluxes. During the past 100+ years approximately 60% of the Great Plains grasslands have been converted to crop production. This has resulted in increased N₂O emissions, decreased CH₄ uptake, and depletion of soil organic matter (SOM). However, appropriate use of land management can reduce GHG gas emissions from agricultural systems while maintaining or increasing crop yields. In recent years improved management systems have been introduced which conserve and enhance SOM. The DAYCENT ecosystem model was used to compare the effects of converting Great Plains grasslands to crop production and the effects of different management on net GHG fluxes (GHG_net) and crop yields for agricultural systems in the Great Plains of the USA. Improved management includes conversion from intensive tillage to no-till cultivation, and reduction of summer fallow periods by replacing continuous winter wheat cropping with alternative rotations that are economically viable for different climate regimes within the Great Plains. Changes in soil organic carbon, N₂O emissions, CH₄ uptake, CO₂ fluxes, and the CO{_2} costs of N fertilizer production were converted to a common unit of CO₂-C equivalents and summed to obtain GHG_net. At the regional level, grassland systems are neutral or small GHG_net sinks, dryland agriculture is a source, irrigated agriculture is a minor sink, and improved management is a major sink.