Cultivation effects on soil carbon and nitrogen contents at depth in the Russian chernozem

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.