Using nitrification inhibitors and deep placement to tackle the trade‐offs between NH₃ and N₂O emissions in global croplands

Abstract

Ammonia (NH3) and nitrous oxide (N2O) are two important air pollutants that have major impacts on climate change and biodiversity losses. Agriculture represents their largest source and effective mitigation measures of individual gases have been well studied. However, the interactions and trade‐offs between NH3 and N2O emissions remain uncertain. Here, we report the results of a two‐year field experiment in a wheat‐maize rotation in the North China Plain (NCP), a global hotspot of reactive N emissions. Our analysis is supported by a literature synthesis of global croplands, to understand the interactions between NH3 and N2O emissions and to develop the most effective approaches to jointly mitigate NH3 and N2O emissions. Field results indicated that deep placement of urea with nitrification inhibitors (NIs) reduced both emissions of NH3 by 67% to 90% and N2O by 73% to 100%, respectively, in comparison with surface broadcast urea which is the common farmers’ practice. But, deep placement of urea, surface broadcast urea with NIs, and application of urea with urease inhibitors probably led to trade‐offs between the two gases, with a mitigation potential of −201% to 101% for NH3 and −112% to 89% for N2O. The literature synthesis showed that deep placement of urea with NIs had an emission factor of 1.53%‐4.02% for NH3 and 0.22%‐0.36% for N2O, which were much lower than other fertilization regimes and the default values recommended by IPCC guidelines. This would translate to a reduction of 3.86–5.47 Tg N yr−1 of NH3 and 0.41–0.50 Tg N yr−1 of N2O emissions, respectively, when adopting deep placement of urea with NIs (relative to current practice) in global croplands. We conclude that the combination of NIs and deep placement of urea can successfully tackle the trade‐offs between NH3 and N2O emissions, therefore avoiding N pollution swapping in global croplands.

Closing the Nutrient Loop—The New Approaches to Recovering Biomass Minerals during the Biorefinery Processes

“…The agricultural systems that promote soil carbon sequestration also stimulate nitrification and the subsequent release of nitrous oxide [528][529][530]. Nitrification inhibitors are a "double-edged sword" [15] that could promote ammonia emissions from soil [531].…”

Greenhouse Gas and Ammonia Emission Mitigation Priorities for Uk Policy Targets

“…Urease is an enzyme contributing to the breakdown of urea to ammonium, which can be readily volatilized to NH3 and so UIs contribute to the reduction of NH3 emissions. In addition to a reduction in NH3 and N2O emissions, the use of NIs and UIs lowers the degree to which N is leached to surface and ground waters, contributing to a reduction of indirect emissions [31] . UIs also improve the efficiency of urea, bringing it in line with N-fertilizers (such as ammonium nitrate), which can either improve yield due to better N use or allow for reduced N application rates.…”

“…Lower quantities of synthetic N-fertilizer applied will also cause a reduction in GHGs from fertilizer manufacturing. There is a potential for increased NH3 loss when NIs and UIs are used in combination due to the buildup of soil ammonium [31] . In addition, there are potential mitigation gains with minimal negative trade-offs with natural alternatives to chemical UIs [39] which still need to be explored.…”

One-Time Deep Application of Nitrogen Fertilizer: A Potential Measure of Ammonia Mitigation in Grainland

“…(3) There is a lack of analysis on the comprehensive environmental effect of one-time deep application in the field. For example, some studies found that concentrated deep application would increase the risk of nitrogen leaching and N 2 O emission loss [21,22]. It is necessary to optimize the one-time fertilization technology to reduce the total loss of nitrogen and improve its utilization efficiency.…”