Temporal Soil Carbon Change in the Northern Great Plains of the U. S.

In the early 1990’s, 28 paired cropland-undisturbed grassland sites were sampled across Major Land Resource Area (MLRA) 54 of southwestern North Dakota.  The paired sites included long-term cropland areas with undisturbed (untilled) grassland areas located within <100 meters of each other on similar soils.  At the initial sampling, the cropland sites had been previously managed in a crop-fallow culture.  Since then, crop fallow has evolved into primarily continuous cropping with no-till management.  In 2010, 9 of the previously sampled sites representing three soil series were resampled to evaluate long-term soil C changes occurring over nearly two decades time. In general, SOC increased for two of the soils at the native sites and decreased across all three soils at the cultivated sites in the upper 50 cm of the soils.  SIC increased for two of the soils for both the cultivated and native sites and decreased for one of the soils across both management types.  However, most of the SIC change occurred below 30 cm.