Crop rotation and the impact on soil carbon in the U.S. Corn Belt

Soils are receiving increasing attention as carbon sinks that can reduce atmospheric CO₂. While common Best Management Practices (BMP), such as cover crops, reduced or minimum tillage, and advanced nutrient management, have been considered as alternatives to build soil carbon storage in managed crop fields, crop-species choices have often been overlooked. This paper uses the Rapid Carbon Assessment (RaCA) data from U.S. Department of Agriculture (USDA), to examine how the rotation of two of the most widely used crops in the U.S., corn and soybeans, influences Soil Organic Carbon (SOC) stocks. We show that at the depths of 0 to 100 cm, corn is correlated with a higher level of SOC stocks than soybeans, and the more years that corn is cultivated the higher the SOC stocks. Specifically, an additional year of corn planted every 3 years is estimated to increase SOC stocks at depths of 0 to 100 cm by 25.1%. Based on our analysis, were all the land in the U.S. states of Ohio, Indiana, Iowa, and Illinois that are currently either mono-cropped with soybeans or follow some sort of soybean-corn rotation converted to corn mono-cropping, the estimated gain in SOC would be 896.7 million Mg C (1 Megagram = 1 ton). This represents a theoretical upper limit for SOC improvements. If current rotational practices were shifted such that corn was planted in 2 of every 3 years in the same region, the theoretical increase in SOC stocks is estimated to be 172.9 million Mg C. Multiplying this result by a Social Cost of Carbon priced at $678/t C in 2020 U.S. dollars (Rennert et al. in Nature 610:687-692, 2022), the total benefits are estimated at $117 billion.