Adding inhibitors to manure injections can mitigate nitrous oxide emissions from barley croplands

Increasing contributions of nitrous oxide (N2O) from agriculture to the atmosphere is a concern. Manure is often used in croplands as a source of nutrients, but this practice can contribute to the release of N2O. We quantified N2O emissions from barley fields after repeated injections of liquid manure in the fall or spring with or without nitrification inhibitors (NIs: DMPP and nitrapyrin) in Central Alberta, Canada. Flux measurements were done with surface chambers from soil thawing to freezing. Soil moisture, ammonium and nitrate were repeatedly measured. Across all manure treatments, annual N2O emissions ranged broadly from 1.3 up to 15.8 kg N2O-N ha(-1), and likewise, the direct emission factor (EFd) varied from 0.23 up to 2.91%. When comparing the manure injections without NIs, spring-manure had higher annual N2O EFd than fall-manure. The effectiveness of NIs on reducing emissions was only evident in moist soils (up to 52% emission reduction). The soil during the spring thaw after the last manure injections was very wet, and this generated high N2O emissions from soils that had received repeated manure injections in the previous years. We interpreted this result as an increased differential residual effect in soils amended with spring-manure in the previous growing season. This outcome supports the need to account for emissions in succeeding springs when estimating N2O EFd of manure injections. Neglecting this residual spring-thaw N2O emission would lead to a substantial underestimation of year-round EFd. Across all treatment combinations, increased spring-thaw N2O emissions were associated with increases in both moisture and postharvest nitrate in these heavily-manured soils. Although injecting liquid manure raised N2O emissions, admixing NIs showed a strong mitigation role.