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. Modern Agriculture 1(1), 4–12.
2. Gu, B. et al. (2023). Cost-effective mitigation of nitrogen pollution from global croplands. Nature 613(7942), 77–84.
3. Tian, H. et al. (2020). A comprehensive quantification of global nitrous oxide sources and sinks. 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. 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. Global Change Biology 16(6), 1837–1846.

Source

Imported from 100 essential questions for the future of agriculture, question 16, 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.