The Corn Belt’s exceptional productivity depends on high soil organic carbon and nutrient stocks (that is, the amount of carbon and nutrients stored in the soil). However, there is growing concern among scientists and farmers that soil carbon, nitrogen, and phosphorus stocks in corn-based cropping systems may be declining as a result of outputs that exceed inputs. The lack of certainty about the status of soil carbon and nutrient stocks is largely due to the extreme difficulty associated with measurement of inputs, outputs, and stocks of soil organic carbon and nutrients.