STABLE CARBON AND OXYGEN ISOTOPES OF SOIL CARBONATES AT DEPTH IN THE RUSSIAN CHERNOZEM UNDER DIFFERENT LAND USE.

Limited information is available about stable carbon and oxygen composition of soil carbonates at depth in the Russian Chernozem under different land use. This study was conducted to determine the stable isotope geochemistry of disseminated carbonates in the Russian Chernozem, one of the typical soils in grasslands. Three sites were sampled: a native grassland field (not cultivated for at least 300 years), an adjacent 50-year continuous fallow 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. The stable carbon isotope composition of carbonates varied with depth and land use: in the native grassland field [delta]13C was in the range of -6.1-(-7.7)[per mille sign]; in the continuous fallow [delta]13C was in the range of 5.7-(-9.8)[per mille sign] Pee Dee Belemnite (PDB); and in a continuously cropped field [delta]13C was in the range of -5.1-(-10.2)[per mille sign] PDB. The stable oxygen isotope composition of carbonates also varied with depth and land use: in the native grassland field [delta]18O was in the range of -6.9-(-9.4)[per mille sign]; in the continuous fallow [delta]18O was in the range of -6.2-(-10.7)[per mille sign]; and in a continuously cropped field [delta]18O was in the range of -7.0-(-9.4) [per mille sign]. More research is needed to investigate the effect of cultivation on stable isotope signatures of pedogenic carbonates.