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Little is known about changes in soil organic C (SOC) and total N with depth and with land use. We conducted this study to determine the depth of changes in SOC and total N under different management regimes in the chernozem soil. Four sites were sampled: a native grassland field (not cultivated for at least 300 yr), an adjacent 50‐yr continuous‐fallow field, a yearly cut hay field in the V.V. Alekhin Central‐Chernozem Biosphere State Reserve in the Kursk region of Russia, and a continuously cropped field in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as fine‐silty, mixed, frigid Pachic Hapludolls. Soil organic C, total N contents, and bulk densities with depth were compared. Significant reductions in SOC and total N concentrations were detected to a depth of 120 to 130 cm in the 50‐yr continuous‐fallow field and to a depth of 80 cm in the continuously cropped field. Highest reductions were observed in the top 10 cm of soil, where reduction in SOC ranged from 38 to 43% and reduction in total N ranged from 45 to 53%. Significant losses of SOC and total N per equivalent soil mass on an area basis were observed to a depth of 60 cm in the continuously cropped field and to a depth of 100 cm in the 50‐yr continuous‐fallow field.

Little is known about changes in soil inorganic carbon (SIC) stocks with depth and with land use in grassland ecosystems. This study was conducted to determine SIC stocks under different management regimes in the Mollisol, one of the typical soils in grasslands. Four sites were sampled: a native grassland field (not cultivated for at least 300 yr), an adjacent 50-yr continuous fallow field, a yearly cut hay field in the V.V. Alekhin Central-Chernozem Biosphere State Reserve in the Kursk region of Russia, and a continuously cropped field in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as fine-silty, mixed, frigid Pachic Hapludolls. Significant differences occurred in SIC stocks between cultivated and grassland soil. The inorganic carbon stocks in the top 2 m were 107 Mg ha(-1) for the native grassland, 91 Mg ha(-1) for the yearly cut hay field, 242 Mg ha(-1) for the continuously cropped field, and 196 Mg ha(-1) for the 50-yr continuous fallow. The SIC was in the form of calcium carbonate and was mostly stored below the 1-m depth. The largest difference between inorganic carbon stocks was observed between the continuously cropped field and native grassland. The increase in inorganic carbon in the continuously cropped field and continuous fallow was attributed to initial cultivation and fertilization. Soil inorganic carbon in Mollisols is not accounted for in the current global carbon estimates.

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