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Crop residue mass needed to maintain soil organic carbon levels: Can it be determined?

Jane M. F. Johnson, Jeff M. Novak, Gary E. Varvel, Diane E. Stott, Shannon L. Osborne, Douglas L. Karlen, John A. Lamb, John Baker, Paul R. Adler
Bioenergy research 2014 v.7 no.2 pp. 481-490
Zea mays, bioenergy, corn, corn stover, crop residue management, cropping systems, feedstocks, guidelines, models, soil erosion, soil organic carbon
Corn’s (Zea mays L.) stover is a potential nonfood, herbaceous bioenergy feedstock. A vital aspect of utilizing stover for bioenergy production is to establish sustainable harvest criteria that avoid exacerbating soil erosion or degrading soil organic carbon (SOC) levels. Our goal is to empirically estimate the minimum residue return rate required to sustain SOC levels at numerous locations and to identify which macroscale factors affect empirical estimates. Minimum residue return rate is conceptually useful, but only if the study is of long enough duration and a relationship between the rate of residue returned and the change in SOC can be measured. About one third of the Corn Stover Regional Partnership team (Team) sites met these criteria with a minimum residue return rate of 3.9±2.18 Mg stover ha−1 yr−1,n=6. Based on the Team and published corn-based data (n= 35), minimum residue return rate was 6.38 ± 2.19 Mg stover ha−1 yr−1, while including data from other cropping systems (n=49), the rate averaged 5.74±2.36 Mg residue ha−1 yr−1. In broad general terms, keeping about 6 Mg residue ha−1 yr−1 maybe a useful generic rate as a point of discussion; however, these analyses refute that a generic rate represents a universal target on which to base harvest recommendations at a given site. Empirical data are needed to calibrate, validate, and refine process-based models so that valid sustainable harvest rate guidelines are provided to producers, industry, and action agencies.