Walters, Daniel (Univ. of Nebraska, Dept. of Agronomy and Horticulture, 261 Plant Sciences, Lincoln, NE, 68583-0915; Phone: 68583-0915; 402-472-1506; Email: dwalters1@unl.edu)

Full C-Cost Accounting and Global Warming Potential of Irrigated and Rainfed Maize-Based Cropping Systems that Produce Renewable Energy from Grain

D. T. Walters, D. Ginting, K. G. Cassman, H. Yang, S. B. Verma, A. Dobermann, M. Schroeder

The potential of modern maize production systems to mitigate anthropogenic greenhouse gas emissions depends on the ability to sequester more C in soil than is consumed in fossil fuel use or lost as nitrous oxide and methane. Full C-cost accounting quantifies the net balance of CO₂-C equivalents in terms of soil C sequestration versus the embodied CO₂-C emission \'costs\' for all inputs used in crop production (seed, fertilizer, pesticides, and fossil fuels consumption for mechanical operations, transportation, and irrigation). This approach also accounts for the more potent global warming potential of N₂O and CH₄ versus CO₂ to estimate the net effect on global warming potential. Such an analysis was performed for three production-scale no-till cropping systems: (a) irrigated continuous maize, (b) irrigated maize-soybean rotation, and (c) rain fed maize-soybean rotation. Over a 3-year period, net ecosystem exchange was measured by eddy covariance flux towers, fluxes of N₂O and CH₄ at the soil surface were monitored throughout the year, and applied inputs and energy use in field operations and irrigation were recorded. A full C-cost accounting will be reported for these three cropping systems based on a field-level analysis. In addition, the full C-cost accounting will be extended to include bioenergy fuel production using the harvested corn grain to produce ethanol and soybean seed for biodiesel fuel with consequent impact on the overall GHG emission balance and global warming potential.