The agricultural sector is the largest global anthropogenic source of N2O, a powerful greenhouse gas with a global warming potential 298 times that of CO2. Because 92% of agricultural N2O emissions are derived from soil and nutrient management practices, changes in management practices have great potential to mitigate – or exacerbate – agricultural N2O emissions. Our objectives were to identify management practices that mitigate or exacerbate N2O emissions and determine whether management interacts with warming winters to impact N2O emissions. We conducted two agricultural field trials to determine the potential of tillage and manure application methods to reduce N2O emissions, with a focus on conventional versus no till systems and broadcast versus manure injection. We further completed an in lab incubation of agricultural soils from these field trials to determine the impact of manure application methods on N2O emissions during wintertime thaws.
Results/Conclusions
Through these on-farm and laboratory experiments, we found that, while tillage practice had little impact on N2O emissions, manure injection increased N2O emissions relative to broadcast. When manure application was in the fall, pulses were relatively small, but elevated N2O emissions continued into the winter. In contrast, spring manure application resulted in larger, but shorter-lived, N2O pulses. Overall, emissions from manure injection treatments were 2.5 times larger than broadcast plots at an average of approximately 120 g N2O-N ha-1 day-1 during the growing season (vs. approximately 50 g N2O-N ha-1 day-1 in broadcast treatments). Finally, even with spring-only manure application, we saw effects of injection versus broadcast application during wintertime thaws: soils with manure injection released nearly double the amount of N2O relative to soil with broadcast manure application. Our results suggest that management can dramatically impact N2O emissions, and that these management decisions may interact with warmer winters to further increase non-growing season emissions of N2O.