Manure Application Decisions Impact Nitrous Oxide and Carbon Dioxide Emissions during Non‐Growing Season Thaws

Abstract

Core Ideas Manure injection increased N2O emissions vs. broadcast and broadcast + plow application. Winter thaws increased N2O and CO2 emissions, particularly in soils injected with manure. The impacts of manure application decisions may extend beyond the growing season to influence N2O and CO2 fluxes during winter thaw events. Climate and agricultural management are strong drivers of greenhouse gas (GHG) emissions, but little is known about potential interactions among these drivers. Climate change will likely increase the frequency of wintertime thaws in northern agricultural systems, which have been shown to induce large pulses of carbon dioxide (CO2) and nitrous oxide (N2O). We tested the hypothesis that different manure application practices would interact with thaw events to produce GHG emission pulses of different sizes. Specifically, we expected manure injection would increase CO2 and N2O emissions relative to other manure application methods by enhancing subsurface microbial substrate availability. We conducted a laboratory incubation study with frozen, intact soil cores from a continuous corn (Zea mays L.) system under three manure application methods: broadcast, broadcast + plow, and injection. Cores were subjected to three temperature treatments over 8 d: frozen (−7°C), freeze–thaw (alternating −7 and 5°C), and thaw (5°C). In the freeze–thaw and thaw treatments, cumulative N2O emissions were 2 to 20 times greater in injected versus broadcast treatments (6.5 mg N2O‐N m–2 averaged across broadcast treatments); cumulative CO2 emissions were up to two times higher in injected versus broadcast treatments (1017 mg CO2–C m–2 averaged across broadcast treatments). Our results suggest that the impacts of manure application choices extend beyond the growing season to increase N2O and CO2 emissions during wintertime thaws, potentially interacting with a warming climate to increase GHG emissions.