Abstract

This study investigated the effects of two types of grasslands conversion to croplands on soil organic carbon (SOC) in Bashang area where it is a typical agro-pastoral ecotone of Northern China using a pare-site method. The results showed that the SOC contents and densities decreased with increasing soil depth. The soil bulk density and SOC content significantly decreased in the upper horizon after the grasslands was converted into croplands. The SOC densities were approximately 2.3 - 2.7 and 4.2 - 9.1 kg C m^-2 in the upper horizons of site 1 and site 2, respectively, with significant differences between grasslands and croplands. The SOC densities up to 60 cm depth were much higher in site 2 (intrazonal grassland-cropland) than in site 1 (zonal grassland-cropland), reaching approximately 13.24 - 22.49 and 5.36 - 6.49 kg C m^-2, respectively. The conversion of grasslands to croplands induced a moderate loss of SOC, with a range of - 4 to 55% for the 0 - 60 cm depth over about 20-year period. To conserve the present status, potential conversion should be banned in both zonal and intrazonal grassland, the zonal grassland should be enforced “turning cropland to grassland” policy, and the intrazonal grassland be reasonably used.

Key words: Agro-pastoral ecotone, conversion, land use, soil organic carbon, zonal and intrazonal grasslands.