Corn stover harvest reduces soil CO2 fluxes but increases overall C losses

Authors: O'Brien, Peter; Sauer, Thomas; ARCHONTOULIS, SOTIRIOS - Iowa State University; KARLEN, DOUGLAS - Former ARS Employee; LAIRD, DAVID - Iowa State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2020
Publication Date: 9/4/2020
Citation: O'Brien, P.L., Sauer, T.J., Archontoulis, S., Karlen, D.L., Laird, D. 2020. Corn stover harvest reduces soil CO2 fluxes but increases overall C losses. Global Change Biology Bioenergy. 12(11):894-909. https://doi.org/10.1111/gcbb.12742.
DOI: https://doi.org/10.1111/gcbb.12742

Interpretive Summary: Over the past two decades, corn (Zea mays L.) stover harvest has been increasing to support the increasing market for biofuel production. Corn stover is an abundant, easily accessible feedstock for bioenergy production, and removing it at appropriate rates may be sustainable and even increase corn grain yields. However, excessive stover removal may result in long-term damage to soil C pools, posing a risk to soil quality and crop production potential. In addition to directly removing C from the system as part of the stover, stover removal also affects other components of the C cycling. Soil CO2 fluxes are an important component of the C cycle that can be altered when crop residue (i.e., corn stover) is removed. We measured the effects of three levels of stover harvest (none, moderate, and high) on soil CO2 fluxes in three continuous corn systems: (1) no tillage and no biochar applications; (2) chisel plowing with biochar amendments; and (3) chisel plowing without biochar amendments. Over three years, we found that measurements from static gas sampling chambers showed no differences between stover harvest levels or agronomic management practices. However, this data enabled us to create a model to estimate season long CO2-C fluxes using the Agricultural Production Systems sIMulator (APSIM). The estimated annual total for C loss via CO2 (i.e., CO2-C) did not differ among the three systems. However, the moderate (approximately 30%) rate of stover removal reduced CO2-C losses by nearly 10% compared to no stover removal, and high (approximately 60%) stover removal rate reduced CO2-C losses by more than 22%. Despite this reduction in CO2 fluxes, the sum of CO2-C and C removed in stover exceeded the CO2-C losses in systems without stover removal. This finding indicates that stover removal at these rates will eventually result in soil C depletion in these systems, though declines in soil C were not evident after three years. The application of biochar increased soil C levels, suggesting that it may be used to offset some C losses. These findings are useful to land managers, agronomists, and producers because they help quantify the true impact of stover removal on soil properties and should be used to guide decisions related to short-term and long-term goals in these agroecosystems.

Technical Abstract: Harvesting corn (Zea mays L.) stover for use as bioenergy feedstock may provide short-term economic benefits and perhaps improve grain yield in continuous corn systems. However, excessive stover removal may lead to long-term depletion of soil C stocks. We measured an important component of the soil C balance, CO2 fluxes, under three stover harvest treatments (none, moderate, and high) in three continuous corn systems: (1) no tillage and no biochar applications; (2) chisel plowing with biochar amendments; and (3) chisel plowing without biochar amendments. We sampled static chambers 14, 13, and 15 times in 2010, 2011, and 2012, respectively, and used these measurements to calibrate the Agricultural Production Systems sIMulator (APSIM) model to estimate cumulative CO2 fluxes. Although total CO2-C loss did not differ among the three systems, both moderate (approximately 30%) and high (approximately 60%) rates of stover removal reduced CO2-C losses by nearly 10% and more than 22%, respectively. Despite these reductions in CO2 flux, the sum of CO2-C and stover C removal exceeded CO2-C losses in systems without stover removal by up to 1000 kg C ha-1 yr-1. This suggests that stover removal may result in soil C depletion for the soil and crop management practices used in this study, though none was evident after three years. Application of biochar did increase soil C levels, suggesting it may be able to offset some C losses. Overall, these findings indicate that for sustainable, highly productive agroecosystems that include stover harvest, agronomic management practices must be optimized to minimize C losses and maintain soil quality.