ABSTRACT

The Morrow Plots, considered the oldest continuous study in the United States, are at the University of Illinois. They were established in 1876 to study the effects of crop rotations and fertilization on yields. Long-term cropping system studies near Wooster, Ohio show that continuous corn plots had the largest decline in soil organic matter (SOM) and nitrogen. The literature available for documentation of the effects of erosion from long-term cropping from controlled experiments is limited. The importance of SOM as a soil constituent and its contributions to plant growth has long been recognized. SOM is an important component of the current concept of soil quality, the definition of which is evolving. The amount of organic matter in a soil is dependent upon a complex set of interactions of physical, chemical, and biological processes. Quantitative methods used to determine SOM contents are variable.