A regional comparison of carbon in cultivated and uncultivated alfisols and mollisols in the central United States

Abstract Several estimates of the size of the global pool of organic carbon in soil have been made, but changes in soil carbon following cultivation have not been adequately quantified. In this paper, data from 303 loess-derived soil samples, primarily Alfisols and Mollisols from the central United States, were used to estimate differences in the carbon content of cultivated and uncultivated soils. The 40% average difference in carbon concentration to a 15-cm depth between all cultivated and uncultivated soils in this study confirmed concentration differences previously reported for the plowed layer. The carbon content of the total profile however, was 28% lower in cultivated vs uncultivated Udalfs and 11% greater in cultivated vs uncultivated Udolls. Unvultivated Udolls were from only one soil series and did not adequately represent the region sampled. Series comparisons indicated that the differences in Udolls are similar to the differences in Udalfs. Carbon was lost primarily from the plowed layer. The distribution of carbon in some profiles of cultivated and uncultivated soils indicated that losses from the plowed layer may have been partially balanced in some soils by an increase in the carbon content of lower layers.