January 31, 2024 | Nature | Source |
Introduction: Crop production contributes significantly to atmospheric ammonia (NH3) emissions, which pose risks to air quality, human health, and ecosystems. However, accurately estimating global NH3 emissions from croplands has been challenging due to data limitations, hindering the identification of effective mitigation strategies. In this study, a Chinese research team from Southern University of Science and Technology worked with other researchers from China and US in developing a machine learning model from a comprehensive dataset of field observations, generate crop-specific and spatially explicit NH3 emission factors globally.
Key findings: The analysis revealed that global NH3 emissions from rice, wheat, and maize fields in 2018 were estimated at 4.3 ± 1.0 Tg N yr−1, lower than previous estimates which did not fully account for fertilizer management practices. By spatially optimizing fertilizer management based on the machine learning model, NH3 emissions could potentially be reduced by about 38% (1.6 ± 0.4 Tg N yr−1) without altering total fertilizer nitrogen inputs. Specifically, significant reductions of 47% for rice, 27% for maize, and 26% for wheat cultivation are projected.
Under future climate change scenarios, NH3 emissions are expected to increase by 4.0 ± 2.7% under a sustainable development pathway (SSP1–2.6) and 5.5 ± 5.7% under a high-emission scenario (SSP5–8.5) by 2030–2060. However, targeted fertilizer management strategies have the potential to mitigate these increases.
Figure | EFs conditioned on management practices and importance analysis. The outer circle shows the global mean EFs produced under different management combinations for our three focal crops. The numbers on the bars represent the EF values (%), which are also shown as the bar heights. The inner circle describes the permutation importance of the features for each continent. The widths of the link lines show the importance of each driver to different categories. EEF, enhanced-efficiency fertilizer; U, urea; AN, ammonium nitrate; SBC, surface broadcast; DPM, deep placement; Mix, a mix of SBC and DPM; NT, no tillage; CT, conventional tillage; Once, once in each growing season; More, twice or more in each growing season; Water input, the sum of cumulative precipitation and irrigation amounts; Tem, cumulative mean daily air temperature during the growing season; SOC, organic carbon content; TN, soil N content; BD, bulk density; Clay, clay content; CEC, cation exchange capacity; Nrate, nitrogen application rate.