Net Greenhouse Gas Emissions from ‘Perennialized’ Annual Cropping Systems in a Cold Climate

'Perennialization' of annual cropping systems, whereby plant cover is continually present, can be supported through the integration of cover crops or intercrops. This form of agricultural diversification is a strategy that mimics natural ecosystems and is postulated to increase agricultural resilience to climate change, decrease nitrous oxide emissions and result in net soil carbon storage. Long-term research has shown that the addition of winter wheat followed by cover crops into a corn-soybean crop rotation can increase soil carbon storage. However, the impact on soil nitrous oxide emissions has not been clearly identified particularly for cold regions characterized by intensive soil freezing that may impact nitrous oxide emitted during thaw. Cover crops can impact freeze-thaw induced emission events by reducing the intensity of soil freezing but can also release substrate that fuels nitrous oxide production. Here we report on field measurements started in May 2018 on two 8-ha fields comparing a simple corn-soybean-soybean rotation with a diverse corn-soybean-winter-wheat crop rotation. Our objective was to compare the net greenhouse gas balance of these two fields including carbon dioxide and nitrous oxide fluxes. The diverse rotation included a two-species cover crop mixture (annual ryegrass and crimson clover) under-seeded to corn at the 6^th leaf stage and a four-species cover crop mixture (crimson clover, cereal rye, oats, and daikon radish) planted after winter-wheat harvest. Micrometeorological methods were deployed to measure net ecosystem exchange of carbon dioxide (eddy covariance method) and nitrous oxide fluxes (flux-gradient method). Preliminary results for one complete cycle of the 3-year rotation will be presented and discussed in terms of how annual cropping systems can meet net zero emission goals.