Can Winter Rye be a Carbon Sink Energy Source? a Biophysically-Modeled Case Study.

The use of winter crops in existing agriculture systems is gaining attention as a food-neutral source of plant biomass for biofuel production. To date, sustainability metrics for these winter crop systems have not been fully investigated to understand the environmental trade-offs between growing the same species as an energy crop, with fertilizer and biomass harvest, versus as a cover crop for conservation purposes, without fertilizer or biomass removal. These metrics are challenging to study due to limited data and a wide range of environments and management systems in which winter crops are grown (Salméron et al., 2010). Given the limitations in experimental data, the biophysical agriculture model, CYCLES, was used to simulate crop growth and assess the response for winter rye with respect to the following sustainability metrics: annual change in soil organic carbon, nitrogen use efficiency, and carbon dioxide emissions reduced from the use of biofuel. Winter rye was selected as a model winter energy crop, and is currently grown as both a cover crop and as dairy forage in the northeastern United States.

Winter rye production was modeled in 4 different cropping scenarios in a 2 year rotation with corn and soybean. These scenarios were compared to the conventional practices of winter fallow and as a cover crop, the latter tilling the winter rye in spring before planting a cash crop. Each scenario was modeled over a 29 year simulation at 3 locations in the northeast United States, using 2 soil types common in the area. Results show improvement in nitrogen use efficiency (Harvested N/N supply) when cropping systems are managed for biofuel production compared to conventional practices and a decrease in anthropogenic carbon dioxide emissions due to agricultural management. Surprisingly, results showed the reduction in carbon dioxide emissions were significantly influenced by the initial soil conditions of the fields. These results highlight the importance of local ecosystem context on the outcome. Results provide insight into the sustainability of these cropping systems and offer management guidance.