University of Reading study links soil nitrogen coordination to lower farm emissions

The University of Reading reported on 25 September that a global analysis linked better coordination of soil nitrogen processes to lower farm emissions. Drawing on 2,235 paired observations from 210 experimental sites worldwide, the researchers found lower average nitrous oxide and ammonia emissions when organic inputs replaced synthetic fertiliser. The finding matters because it points to how nitrogen moves through soil, rather than the fertiliser label alone, as a possible guide to cutting pollution.

The Nature Communications study, published on 24 August, compared experiments in which organic amendments replaced synthetic fertiliser at equal nitrogen inputs. Across those comparisons, nitrous oxide emissions were 21.8% lower on average and ammonia emissions were 40.6% lower. Those are pooled results from earlier experiments, not measured reductions that every farm could expect from changing its fertiliser.

How the soil nitrogen study measured coordination

The authors adapted a measure of synchrony from community ecology to examine how four soil processes work together: mineralization, immobilization, nitrification and denitrification. In broad terms, these processes release nitrogen from organic material, take it up into soil organisms, or transform it into other chemical forms. The researchers used their combined behaviour to investigate why nitrogen applied to crops can instead leave fields as gases.

The paper reports that mismatches between nitrification and denitrification accounted for about half the variation in nitrous oxide emissions in its analysis. Mismatches between mineralization and immobilization explained more than one-third of the variation in ammonia emissions. The authors say this coordination measure predicted the two gases more accurately than looking at individual processes alone. That makes it a proposed tool for understanding emissions across experiments, rather than a direct measurement of what will happen after a particular farmer changes practice.

Why nitrous oxide and ammonia losses matter

The United Nations Environment Programme identifies agriculture, particularly synthetic fertilisers and manure, as a major source of nitrous oxide. Its 2024 Global Nitrous Oxide Assessment describes the gas as a climate threat that also depletes the ozone layer. That assessment supplies context for the importance of reducing agricultural emissions; it does not independently test the Reading team's synchrony measure.

Ammonia poses a different problem. UNEP says it is released from the handling and spreading of animal manure and from synthetic fertiliser application. Once in the air, ammonia contributes to fine particulate pollution. Lower ammonia losses therefore matter for air quality as well as for the broader problem of using nitrogen efficiently in food production. The two gases have different environmental effects, so the study examined them separately.

What the findings mean for fertiliser decisions

The researchers screened agricultural experiments that compared equal nitrogen inputs and lasted at least one crop-growing season. Their literature search covered papers available through 10 November 2024. Combining those experiments allows a broad comparison across settings, but the pooled result covers different crops, soils, climates, amendments and study durations. It cannot supply a fertiliser rate or predict the emissions outcome for an individual field.

The team also modeled where organic substitution might offer larger gains. Its projections put potential nitrous oxide reductions at about 40.7% in European croplands and potential ammonia reductions at about 46.1% in African croplands. These figures are regional estimates from the model, not observed reductions across all farms in either region. They should be read separately from the smaller average reductions found in the pooled experimental comparisons.

Professor Zhaolei Li, a senior author, said the approach could improve models of agricultural emissions and help assess management practices. Co-author Professor Simon Willcock cautioned that the message is not simply to replace synthetic fertiliser with organic fertiliser: management needs to account for the whole soil system. The paper's exceptions to its average results reinforce that distinction. Organic amendments differ, and their effects on nitrogen losses cannot be inferred from the overall average alone.

For a farmer considering a change, the study identifies a question to test locally: how a proposed input affects the soil processes that release or retain nitrogen, alongside crop needs and measured emissions. The published analysis does not establish that a particular switch will reproduce its pooled average or its modeled regional gains. Its immediate contribution is a framework for comparing nitrogen losses across experiments and refining predictions, with field-specific outcomes still to be established.