Crop Yield, Economics and Soil Microbiome Changes in Corn Cropping Systems.

Farmers recognize and take advantage of the yield effect when crops are rotated. In the Midwest U.S., either continuous corn or alternating corn-soybean systems are dominant. Farmers are reluctant to deviate from this corn based system due to economics and policy incentives. Depending upon year, rotated corn increases yield -9 to 54% over continuous corn with an average response of 13 to 15%. Rotated soybean increases yield -8 to 43% over continuous soybean with an average response of 10 to 18%. Adding a third crop to the rotation further increases yield of all crops 0 to 7%, but often a sustainable market is not available for the added crop. The economics of these corn-based systems favor the corn-soybean rotation over continuous corn by $164 ha^-1 yr^-1. Even though farmers take advantage of the rotation effect, it is not understood. A number of hypotheses have been put forward and evaluated but none are supported by empirical evidence. However, modern soil microbiome techniques have identified changes in microbial community species diversity, richness, and functional genomic groups depending upon the crop grown. These techniques offer the best potential for better understanding soil microbiome dynamics, interactions and ultimately the rotation effect on crop yield.