Cutting nitrogen losses from saline soils by 59% could produce net global benefits of $24.5 billion a year, study finds

Salt-affected cropland is leaking far more fertilizer nitrogen into the environment than previously quantified, and fixing it could be one of agriculture’s largest untapped nitrogen savings. A global analysis published in Nature Food finds that saline soils nitrogen losses are 61% higher than on comparable non-saline land, and that ten established management practices could cut those losses by 59%, or about 2.5 million tonnes of nitrogen a year, while raising crop output.

The study, led by Wen Wen and Baojing Gu of Zhejiang University with colleagues at the International Institute for Applied Systems Analysis (IIASA) and the University of Maryland, estimates net global benefits of $24.5 billion a year, with an uncertainty range of plus or minus $11.8 billion. For fertilizer suppliers and agronomists, the finding frames salinity as a nutrient-efficiency problem as well as a yield problem.

Why saline soils nitrogen losses are so high

More than a billion hectares of farmland are affected by salt, which builds up in the root zone as irrigation water evaporates and saline groundwater moves inland. The researchers built a spatially explicit nitrogen budget for the world’s saline croplands at a 0.5-degree resolution, combining a global soil salinity map with European Space Agency cropland data, the IMAGE integrated assessment model, the CHANS nitrogen budget model and MODIS satellite vegetation data.

By pairing salt-affected and unaffected fields, the team isolated the salinity effect. Salinity raised nitrogen inputs on affected cropland by 13% while cutting the nitrogen harvested in crops by 7%. In practice, farmers apply more fertilizer to offset weak yields, but stressed crops and soil microbes take up less of it.

The surplus escapes as ammonia volatilization, nitrous oxide, nitrogen oxides and nitrate leaching. Salt stress suppresses the microbial communities that drive nitrification and denitrification, and impairs root growth and water uptake. The nitrous oxide share matters for climate accounting, since the gas is roughly 300 times more potent than carbon dioxide over a century.

Ten practices to cut saline soils nitrogen losses

The authors synthesized ten categories of salinity management from field studies. They range from improved irrigation and drainage that flush salts below the root zone, to soil amendments such as biochar, to biological approaches including halophyte-based remediation and salt-tolerant crop varieties. Widespread adoption would reduce annual reactive nitrogen losses from saline croplands by 59% and lift crop production at the same time.

The scale is notable. A 2.5 million tonne annual nitrogen saving is comparable to the total mitigation potential of some entire national farm systems, a comparison that suggests saline soil management deserves a place alongside fertilizer optimization and manure management in nitrogen pollution control.

Where the gains are concentrated

Benefits cluster in large irrigated basins. China, Pakistan and Indonesia have the biggest aggregate mitigation opportunities, reflecting the extent of salt-affected irrigated land in their major river systems. Egypt stands out for the highest benefits per hectare, driven by intensive irrigated farming and severe salinity in the Nile Delta.

For the fertilizer industry, those markets combine high nitrogen use with poor efficiency on salt-affected land. Better salinity management would not necessarily mean less fertilizer sold, but more of each tonne applied would end up in the crop. That aligns with the broader shift toward nutrient use efficiency that regulators and buyers increasingly expect.

Limits and what comes next

Constraints remain. The ten practice categories differ widely in cost, technical difficulty and suitability across soils and water regimes, and effect sizes from field trials may not transfer evenly to every salt-affected landscape. Drainage and leaching schemes need water infrastructure that many smallholder systems lack, and amendments like biochar remain costly at scale.

The findings add to a growing body of work linking soil biology to nitrogen efficiency, including recent research showing that soil microbiome predators can boost plant biomass and may cut nitrogen fertilizer needs. The authors argue that saline soil restoration fits climate-smart agriculture and climate finance, since it raises output, cuts emissions and returns a net economic gain. Whether governments in the most affected basins fund drainage and soil programs at scale will decide how much of the modeled saving turns into real reductions. The full paper is available via Nature Food.

Source: Bioengineer.org