Annual Budgets of Soil Organic Carbon in the Prairie Pothole Area of North Dakota Between 1998 and 2007.

Soil fertility and sustainability are, to a great extent, dependent on soil organic carbon dynamics which are, however, primarily constrained by changes in land use, land management, and climate variables. In this study, the general ensemble biogeochemical modeling system (GEMS) was used to quantify annual soil organic carbon budgets within a typical Prairie Pothole area of North Dakota between 1998 and 2007. The model inputs included annual cropland data layers, historical climate records, a soil wetness index map, an irrigation distribution map, information from the SSURGO database on soil texture and organic matter, and management practice information. Our results show that the top 100-cm depth of soil across the study area was a carbon source at an annual rate of 80 kg C ha^-1yr^-1 during the study period, varying with land use type, and the difference (from previous year) in annual budget demonstrated a marked intra-annual variability. Generally, the soil carbon dynamics within natural ecosystems were principally controlled by climate and the conversions of land use types, and the carbon sources or sinks within managed ecosystems were dominantly governed by annual changes in cropping system and management practices. The annual rate of change for soil organic carbon stocks in all kinds of lands significantly depended on the magnitude of the antecedent soil carbon content.