The role of cover crops in reducing nitrous oxide emissions and the impact of soil freeze-thaw events

Background/Question/Methods

The use of cover crops to increase plant diversity in annual cropping systems can lead to many environmental benefits, and there is growing interest in understanding cover crop effects on greenhouse gas emissions. However, the impact of cover crops on soil nitrous oxide (N2O) emissions – which agricultural soils are the largest contributor – has not been clearly identified particularly in the non-growing season in cold regions. Our objective was to quantify the effects of cover crop diversification on N2O emissions from annual cropping systems, paying special attention to the non-growing season when soil temperature can vary above and below freezing. Using the flux gradient method, field-scale measurements were started in May 2018 on two 8-hectare fields comparing a simple crop rotation with a diverse crop rotation that included cover crops.

Results/Conclusions

Preliminary results for one complete cycle of a three-year rotation show distinct cover crop effects on N2O emissions at key environmental and management events. Notably, during the non-growing season, freeze-thaw events led to spikes in N2O emissions that markedly contributes to cumulative emissions from the fields. Cover crops differentially affected N2O emissions following freeze-thaw depending on when the freeze-thaw event occurred in the winter, highlighting changing impacts of the abiotic and biotic effects of cover crops on soil nitrogen cycling over time. A complementary controlled experiment using microcosms is underway designed to distinguish the plant-soil mechanisms that drive emission differences observed in the field experiments. Our research is intended to inform cover crop management and evaluate the role of plant diversification in meeting climate change mitigation goals