Using Apsim to Optimize Biochar Application Rates for Midwest Corn-Bioenergy Cropping Systems.

Midwestern farms are the largest potential source of crop residues for bioenergy production, however, there is a need for new more sustainable practices to compensate for the negative effects of residue harvesting on soil quality. Biochar applications could offset the potential negative effects of residue removal and enhance agricultural productivity while simultaneously sequestering carbon. Here, we use a biochar model recently developed for the Agricultural Production Systems sIMulator (APSIM), a farming systems model capable of integrating many aspects of agro-ecosystem complexity, to predict the long-term impacts of biochar applications and residue harvesting on agro-ecosystem performance. We used a long-term experimental dataset that included soil, yield, and management data from a field study in central Iowa, which includes residue removal and crop rotations, to calibrate and validate the APSIM biochar model. We then applied the model to address the following question: what is the optimum biochar application rate that maximizes productivity and environmental performance of conventional corn and corn-soybean cropping systems in Iowa under different N fertilizer application rates and residue harvesting scenarios? We also employed a cost-benefit analysis to identify the economically optimal biochar application rate from both producer and societal perspectives. Results of model application showed that across all scenarios as biochar application rate increased both continuous corn and corn-soybean rotations had reduced nitrate leaching, increased soil carbon levels, and no impact on corn yields. Preliminary results from the economic analysis indicate that once the crop has sufficient nitrogen, both public and private benefits improve further as residue harvest and biochar application rates increase.