Carbon and nitrogen environmental trade-offs of winter rye cellulosic biomass in the Chesapeake Watershed

Cellulosic biomass from winter crops can complement maize stover harvested from maize (Zea mays L.) – soybean (Glycine max L.) rotations. In this study, we assessed on-field environmental impacts related to carbon (C) and nitrogen (N) by modeling representative agro-ecological conditions prevalent in the mid-Atlantic region of the United States. We used the biophysical model Cycles to simulate management scenarios for maize-soybean cropping systems that included winter rye (Secale cereale L.). The model was used to quantify changes in N losses via nitrate leaching (NO3), emissions of nitrous oxide (N2O) and ammonia (NH3), changes in soil organic carbon, and carbon dioxide equivalent emissions per megajoule (CO2eqMJ−1). Including winter rye in the rotation reduced NO3 leaching over a winter fallow control (77% on average), even when the winter rye was fertilized and regardless of whether stover, winter rye, or both cellulosic feedstocks were harvested. Applying fertilizer to winter rye did however increase NO3 leaching as well as NH3 and N2O emissions. Model results consistently showed fertilizing the winter rye improved both biomass yield and soil C levels compared to unfertilized winter rye, regardless of location, soil, fertilizer type or stover harvest. While it is difficult to simultaneously reduce agricultural nitrogen losses, produce renewable energy and increase soil carbon, results can guide management of these trade-offs while tapping into an abundant energy resource and reducing greenhouse gas emissions.