ABSTRACT
The value of soil organic matter (SOM) has been long recognized. Under cultivated agriculture, crop residues serve as carbon (C) inputs and thus influence both the level and the dynamics of organic matter in soil. Unfortunately, there were no direct data on crop residue inputs under the different cropping systems on Sanborn Field. Because corn, wheat, and soybean constitute major components of Sanborn Field management systems, the chapter focuses on the biological productivity of the crops in small-scale field experiments. The level of SOM under different long-term cropping systems of Sanborn Field is recognized to be related to the annual input of crop residues. The mineralization rates have been observed to vary somewhat with cropping and cultivation practices. Annual losses of soil organic C were estimated using measured soil C contents multiplied by the appropriate mineralization rates determined from earlier work on several of the historical plots.
