Soil carbon in desertified land in relation to site characteristics

Soil organic carbon content (SOC, kg C m−2) and its relation to site characteristics are important in evaluating current regional, continental, and global soil C stores and projecting future changes. Data from 340 soil samples were compiled for 17 different types of desert and sandy land regions of China. The SOC of sandy soil ranged from 0.02 to 4.97 kg C m−2, which is normally distributed in the study (mean=1.12 kg C m−2) for the 0–0.2-m profile and 0.02 to 12.52 kg C m−2 (mean=2.32 kg C m−2) for the 0–1.0-m profile. Variability in SOC contents and bulk density contributed substantially to SOC variation. Regression analysis of climatic and pedological characteristics associated with 340 sandy soils with respect to their SOC indicated that combinations of site characteristics explained up to 80% of the SOC variability. The SOC increased with annual precipitation, and decreasing evaporation and temperature. Vegetative cover, climatic zones, and carbonate carbon were noted for different desert soil types. Regional accumulations of SOC were examined relative to precipitation, evaporation, temperature and elevation. The largest accumulations of pedogenic carbonates were found in calcic soils and in warm, arid areas. In soils under Betula platyphylla, organic carbon accumulations predominated. The top 1.0-m soil layer of natural desertified lands contains some 7.84 Pg of organic carbon and 14.91 Pg of carbonate carbon. The total stored carbon was 1.8-fold the organic carbon alone. Thus, the carbon stored in soil carbonates in desertification prone lands in China is an important factor affecting changes in concentrations of atmospheric carbon dioxide.