Evaluation of soil carbon sequestration in the semi-arid regions of the northern Great Plains

This dissertation presents research on effects of land management on soil carbon (C) sequestration and evaluation of different C sequestration models in the semi-arid climate of southwestern North Dakota subjected to differing land management practices. Soil management plots were established on adjacent areas of undisturbed native grassland (NH plots) and long-term cultivated cropland (CH plots) with similar soils. The NH and CH plots were tilled and either restored to grass with grazing (GG) or without grazing (GU) or seeded into continuous spring wheat (W), spring barley (B), or spring oats (O) under no-till (NT) or conventional tillage (CT) management. Plots of undisturbed native grass (N) within the original grassland area were maintained for comparison with an undisturbed natural system. Changes in soil organic C (OC), inorganic C (IC) and total C (TC) were measured for each management treatment for a 5 year period.;Within the restored grass systems, the OC changes were N > NHGU > CHGU > CHGG > NHGG; CHGG and CHGU lost IC. Within the cropping treatments, C sequestration could be ranked spring wheat > spring barley > spring oats.;Under continuous spring wheat, when compared to the undisturbed grass plots, OC changes were N > NHWNT > CHWNT > CHWCT > NHWCT; CHWNT and NHWNT lost IC; NHWNT lost TC. For continuous spring barley compared to undisturbed grass, OC changes were N > CHBCT > CHBNT > NHBCT > NHBNT; NHBCT and NHBNT lost IC. When continuous spring oats was compared with the undisturbed grass, OC changes were N > CHOCT > CHONT > NHOCT > NHWNT; CHOCT and CHONT lost IC.;A comparison of the Soil Conditioning Index (SCI), COMET-VR and CENTURY Models with actual changes in soil OC showed that, within the limitations of the models, all of the models underestimated the OC sequestered. Further research is needed to evaluate soil C sequestration in rain-fed semi-arid areas of the U.S., especially regarding the effects of soil management changes on soil IC and the total quantity of C stored in the soil profile.