# How can nitrogen emissions from farm soils be cut most effectively?

Fertilised soils release nitrogen as nitrous oxide, a potent greenhouse gas that also depletes stratospheric ozone, and as other reactive gases that pollute the air. Which strategies reduce these losses most, at what cost, and without sacrificing yield?

## Question

What are the most effective strategies to reduce nitrogen emissions from agricultural soils, chiefly nitrous oxide (N₂O) but also nitric oxide and ammonia? Candidates range from fertiliser rate, timing, placement and form to inhibitors, coated fertilisers and soil management, whose effects vary with soil and climate.

## Background

The question is in the theme "mitigating climate change through agriculture" of the 100 essential questions for the future of agriculture, compiled from 419 questions submitted worldwide in 2022; the authors note that crop and livestock production release significant amounts of non-CO₂ greenhouse gases, including nitrous oxide [1]. Because lost nitrogen is wasted fertiliser, cutting losses also saves money, offsetting part of the cost of mitigation [2].

## What is known

- Global N₂O emissions were about 17 Tg of nitrogen a year in 2007–2016. Human-induced emissions, dominated by nitrogen added to croplands, rose by 30% over four decades to 7.3 Tg a year and were mainly responsible for the growth of atmospheric N₂O [3].
- In a meta-analysis of 78 studies (233 site-years), N₂O emissions grew faster than linearly once nitrogen inputs exceeded crop needs, so cuts in over-fertilised systems have a disproportionately large effect [4].
- In field experiments, nitrification inhibitors reduced N₂O emissions by 38% on average and polymer-coated fertilisers by 35%, whereas urease inhibitors were not effective for N₂O [5].
- A synthesis of 1,521 field observations identified 11 measures that cut nitrogen losses from croplands to air and water by 30–70% while raising yields by 10–30%. Applied globally, they would use 21% less fertiliser and cut nitrogen pollution by 32%, with a societal benefit of about USD 476 billion against net costs of about USD 19 billion [2].

## What would count as progress

No single result settles a question like this; contributions like these would move it forward:

- Open, harmonised datasets of field N₂O measurements with management, soil and weather data, to test which measures work where.
- Models that predict site-specific emission reductions from a measure, validated against field trials held out of the fit.
- Long-term trials that report yield, profit and all nitrogen losses (N₂O, ammonia, nitrate leaching) together, to expose trade-offs.

## References

1. Hu, Y. et al. (2023). [100 essential questions for the future of agriculture](https://doi.org/10.1002/moda.5). *Modern Agriculture* 1(1), 4–12.
2. Gu, B. et al. (2023). [Cost-effective mitigation of nitrogen pollution from global croplands](https://doi.org/10.1038/s41586-022-05481-8). *Nature* 613(7942), 77–84.
3. Tian, H. et al. (2020). [A comprehensive quantification of global nitrous oxide sources and sinks](https://doi.org/10.1038/s41586-020-2780-0). *Nature* 586(7828), 248–256.
4. Shcherbak, I. et al. (2014). [Global metaanalysis of the nonlinear response of soil nitrous oxide (N₂O) emissions to fertilizer nitrogen](https://doi.org/10.1073/pnas.1322434111). *Proceedings of the National Academy of Sciences* 111(25), 9199–9204.
5. Akiyama, H. et al. (2010). [Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N₂O and NO emissions from agricultural soils: meta-analysis](https://doi.org/10.1111/j.1365-2486.2009.02031.x). *Global Change Biology* 16(6), 1837–1846.

## Source

Imported from [100 essential questions for the future of agriculture, question 16](https://doi.org/10.1002/moda.5), curated by Hu et al. Listed as open in the source (2023) and still an active research question as of 2026-10-20. The statement above is written in our own words; see the source for the original wording, history and discussion.