Changes in Soil Organic Carbon and Nitrogen as a Result of Cultivation

We assembed and analyzed a data base of soil organic carbon and nitrogen information from over 1100 profiles in order to explore factors related to the changes in storage of soil organic matter resulting from land conversion. The relationship between cultivated and uncultivated organic carbon and nitrogen storage in soils can be described by regression lines with uncultivated storage on the abscissa, and cultivated storage on the ordinate. The slope of the regression lines is less than 1 indicating that the amount of carbon or nitrogen lost is an increasing fraction of the intial amount stored in the soil. Average carbon loss for soils with high initial carbon is 23% for 1-meter depth. Average nitrogen loss for the same depth is 6%. In addition, for soils with very low uncultivated carbon or nitrogen storage, cultivation results in increases in storage. In soils with the same uncultivated carbon contents, profiles with higher C:N ratios lost more carbon than those with low C:N ratios, suggesting that decomposition of organic matter may, in general, be more limited by microbial ability to break carbon bonds than by nitrogen deficiency. For access to the data files, click this link to the CDIAC data transition website: http://cdiac.ess-dive.lbl.gov/programs/CSEQ/terrestrial/postmann1990/postmann1990.html