Through field monitoring and laboratory experiments, they found that deposited NH₃ stimulated N₂O release mainly via ammonia-oxidizing archaea–driven nitrification. Within 500 meters of a pig farm in south-central China, annual soil N₂O emissions reached 69.7 kg N yr⁻¹—about 1.3% of deposited NH₃-N—exceeding the IPCC default emission factor.
Livestock production is the world’s largest anthropogenic source of ammonia, emitting nearly 30 Tg N in 2018—about half of all agricultural NH₃ emissions. China contributes a major share due to rapid expansion of intensive animal farming. Although NH₃ is not itself a greenhouse gas, once deposited in soils it can be microbially converted into N₂O, which has a global warming potential 298 times that of CO₂ and contributes to ozone depletion. Agriculture produces nearly half of global anthropogenic N₂O emissions. While direct N₂O releases from livestock facilities are well documented, the fate of downwind NH₃ deposition and its microbial pathways driving additional soil N₂O emissions remain poorly understood.
A study (DOI: 10.48130/nc-0025-0023) published in Nitrogen Cycling on 28 January 2026 by Jianlin Shen’s team, Chinese Academy of Sciences, highlights livestock-derived ammonia as an overlooked “secondary” source of agricultural greenhouse gas emissions.
To investigate how ammonia exposure from an intensive pig farm influences soil nitrogen dynamics and nitrous oxide emissions, the researchers combined field transect monitoring, controlled laboratory incubations, and molecular analysis of nitrogen-cycle functional genes. In the field, soil samples were collected along north (N) and northeast (NE) transects at distances of 50–500 m from the farm to measure inorganic nitrogen (NO₃⁻-N and NH₄⁺-N) concentrations and N₂O fluxes. Soil NO₃⁻-N and NH₄⁺-N contents generally declined with distance, although correlations were not statistically significant. NH₄⁺-N consistently exceeded NO₃⁻-N along both transects, suggesting greater ammonium input than consumption near the farm. NO₃⁻-N ranged from 0.1–3.4 mg kg⁻¹ (N transect) and 0.1–37.3 mg kg⁻¹ (NE transect), with particularly elevated values at 50 m along the NE transect during September–December. NH₄⁺-N concentrations varied between 1.3–36.3 mg kg⁻¹ (N transect) and 0.8–29.1 mg kg⁻¹ (NE transect), with relatively lower levels in July and August. Simultaneously, field N₂O monitoring showed that soils acted predominantly as net N₂O sources. The N transect exhibited a single emission peak in August–September 2018, while the NE transect showed bimodal peaks in autumn 2018 and spring 2019. Daily fluxes were consistently higher along the N transect (mean 1.2 g N ha⁻¹ d⁻¹) than along the NE transect (0.8 g N ha⁻¹ d⁻¹), and emissions generally decreased with distance from the farm. Laboratory incubation experiments further tested the effects of nitrogen form and soil moisture (40% vs 60% water-filled pore space, WFPS). N₂O emissions peaked within the first three days and were highest under 60% WFPS with urea addition, followed by ammonium nitrate, while 40% WFPS treatments produced the lowest cumulative emissions. Nitrogen-amended soils released up to 105.2 μg N m⁻² over 35 days, with urea generating significantly greater emissions than other treatments. Finally, quantitative PCR revealed that the abundance of ammonia-oxidizing archaea (AOA) amoA genes declined with distance but greatly exceeded ammonia-oxidizing bacteria (AOB) abundance, whereas denitrification genes (nirK, nirS, nosZ) showed no clear spatial trend, indicating a dominant role of AOA-mediated nitrification near the farm.
This study demonstrates that ammonia deposition from intensive livestock farms can generate a measurable secondary source of soil N₂O in surrounding ecosystems. The observed 1.3% emission factor—exceeding the IPCC default—suggests current inventories may underestimate livestock-related climate impacts. Mitigation strategies should therefore extend beyond direct on-farm emissions to include NH₃ control, with improved manure management, dietary adjustments, and ammonia-capture technologies offering broader climate benefits.
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References
DOI
10.48130/nc-0025-0023
Original Souce URL
https://doi.org/10.48130/nc-0025-0023
Funding information
This work was supported by the National Key Research and Development Program of China (Grant No. 2024YFC3711903), and the National Natural Science Foundation of China (Grant No. 42477378).
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