Corn Residue Removal Impact on Topsoil Organic Carbon in a Corn–Soybean Rotation

Corn (Zea mays L.) residue is being considered as a feedstock for biofuels production. The impact of removing corn residue on soil productivity is not well understood. A corn-soybean [Glycine max (L.) Merr.] rotation was established in 2000 to determine the effect of removing corn residue at three rates (37, 55, and 98%) on soil organic carbon (SOC) in the 0- to 5-cm layer of soil after 8 yr. The effect of cover crops {slender wheatgrass [Agropyron caninum (L.) Beauv.] in corn and lentil (Lens culinaris Medik. variety Morton) in soybeans} on SOC was also measured. As the rate of residue removal increased, soil organic matter (SOM), wet aggregate stability (WAS), C/N, and microbial activity decreased significantly. Although the effect was not significant, there was a decrease in SOC as the rate of removal increased. At the high residue removal rate, SOM analyzed by quantitative (13)C NMR contained an abundance of aromatic C structures, suggesting that less humified pools of soil C are not being replenished. The humin fraction of the soil had a reduction in SOC under the medium and high rates of residue removal without a cover crop and is likely beginning to be depleted. Bradford-reactive soil protein and immunoreactive soil protein were higher in soils with cover crops, likely due to increased plant diversity and extending the growing season to allocate more C belowground. Overall, the data suggest that the soil properties indicative of soil quality are negatively impacted by removal of corn residue.