The study was conducted by Mohamed Boullouz, Mohamed Louay Metougui, and Ngonidzashe Chirinda at the Agricultural Innovation and Technology Transfer Center of Mohammed VI Polytechnic University in Ben Guerir, Morocco. Their experimental site sits in a semiarid zone where wheat, the region’s staple cereal, is grown under drip irrigation, a water-saving technique that delivers water and dissolved nutrients directly to the root zone. Drip systems are often promoted as environmentally friendly because they reduce water waste and can improve nitrogen use efficiency. But as this study demonstrates, the climate accounting of such systems depends heavily on which fertilizer goes into the irrigation lines.

The team set up a field trial comparing four mineral nitrogen sources at an identical application rate of 125 kilograms of nitrogen per hectare: conventional urea, ammonium nitrate, a urease-inhibited urea product marketed as Duramon, and a blend of ammonium nitrate and urea. An unfertilized control plot completed the design. Urea is by far the most widely used nitrogen fertilizer on Earth, prized for its high nitrogen content and low cost, but it must first be hydrolyzed in soil to ammonium before plant roots can take it up. That hydrolysis step creates a burst of ammonium and a localized rise in soil pH, conditions that can supercharge the microbial processes, nitrification and denitrification, that produce nitrous oxide as a byproduct.

Over the growing season, the researchers measured cumulative nitrous oxide fluxes using standard chamber-based gas sampling. The results were striking. Plots fertilized with conventional urea emitted 1.84 kilograms of nitrogen per hectare as nitrous oxide, while ammonium nitrate and the ammonium nitrate plus urea blend each emitted just 1.02 kilograms. The urease-inhibited urea fell in between at 1.36 kilograms. The unfertilized control produced 0.28 kilograms, establishing the background emission against which fertilizer-induced losses are judged. Expressed per unit of applied nitrogen, urea emitted 1.82 times more nitrous oxide than ammonium nitrate, even though grain yields across the fertilized treatments were statistically comparable.

Those numbers translate directly into emission factors, the percentage of applied nitrogen that escapes into the atmosphere as nitrous oxide. The Intergovernmental Panel on Climate Change currently instructs national inventory compilers to assume a default emission factor of 0.5 percent for dry climates, a figure meant to represent the average behavior of all nitrogen inputs in water-limited regions. The Moroccan measurements tell a different story. Urea’s emission factor was 1.24 percent, with a bootstrap 95 percent confidence interval of 1.10 to 1.38 percent, meaning it exceeded the IPCC default in every one of the thousands of statistical resamples the team performed. The urease-inhibited urea came in at 0.86 percent, also consistently above the default. Only the nitrate-containing fertilizers, at 0.59 percent each, bracketed the IPCC value, with confidence intervals spanning the 0.5 percent line.

The mechanistic explanation lies in soil microbial ecology. When urea hits moist soil, the enzyme urease cleaves it into ammonium within days, temporarily suppressing nitrite-oxidizing bacteria and creating conditions under which nitrifier denitrification and incomplete nitrification release disproportionate amounts of nitrous oxide. Ammonium nitrate, by contrast, delivers nitrogen already split between its ammonium and nitrate forms, bypassing the hydrolysis spike and smoothing out the microbial activity that drives emissions. Urease inhibitors such as the one in Duramon slow the hydrolysis step, and the study confirmed that they do reduce cumulative emissions relative to plain urea. However, the inhibitor did not significantly reduce yield-scaled emissions, the amount of nitrous oxide released per ton of grain produced, suggesting the technology moderates but does not eliminate the urea penalty.

The implications reach well beyond a single wheat field in Morocco. National greenhouse gas inventories under the Paris Agreement rely on IPCC emission factors, and for countries without extensive local measurement networks, the Tier 1 dry-climate default of 0.5 percent is the working assumption. If urea-dominated irrigated systems in semiarid regions actually emit at rates closer to 1.2 percent, those inventories are systematically undercounting agricultural nitrous oxide, and the mitigation policies built on them are aiming at the wrong target. Conversely, the finding that nitrate-based fertilizers hover near the default suggests that the 0.5 percent figure may be reasonable for some fertilizer types but misleading as a blanket value. The study’s authors argue that non-stratified emission factors, ones that ignore fertilizer source, risk underestimating emissions precisely in the urea-heavy systems that dominate global fertilizer consumption.

What makes the result especially compelling is the absence of a trade-off. Climate mitigation in agriculture often asks farmers to accept lower yields, higher costs, or more complex management in exchange for reduced emissions. Here, switching from urea to ammonium nitrate or a urea-ammonium nitrate blend cut nitrous oxide losses by roughly 45 percent while grain yields remained statistically indistinguishable across treatments. In a semiarid environment where every kilogram of grain matters for food security, and where drip irrigation has already been adopted to conserve scarce water, fertilizer substitution is an immediately actionable lever. The caveat is practical: ammonium nitrate can be more expensive or harder to obtain in some markets, and regulatory restrictions on nitrate fertilizers exist in certain countries due to misuse concerns. But where supply chains allow, the agronomic case is straightforward.

The study also adds an important data point to a growing body of work questioning how well global emission factors capture the diversity of real-world cropping systems. Recent research has highlighted that legacy effects of past nitrogen applications, sampling frequency, and irrigation management can all bias emission factor estimates, sometimes causing systematic underestimation. The Moroccan trial, conducted under the precise water control of drip irrigation, isolates fertilizer source as the dominant variable and shows it is powerful enough to double emissions at a fixed nitrogen rate. For semiarid wheat belts stretching from North Africa through the Middle East and Central Asia, where urea is the default nitrogen source and irrigation is expanding, the message is clear: the molecule carrying the nitrogen matters as much as the amount applied, and climate-smart fertilizer policy should treat fertilizer choice as a first-order decision rather than an afterthought.

Subject of Research: Nitrous oxide emissions and emission factors from different mineral nitrogen fertilizers in drip-irrigated semiarid wheat

Article Title: Mineral nitrogen source controls N2O emissions and emission factors in drip-irrigated semiarid wheat

Article References: Boullouz, M., Metougui, M. L., & Chirinda, N. (2026). Mineral nitrogen source controls N2O emissions and emission factors in drip-irrigated semiarid wheat. Environmental Monitoring and Assessment, 198(10), Article 1099. https://doi.org/10.1007/s10661-026-15963-1

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15963-1

Keywords: nitrous oxide, urea, ammonium nitrate, urease inhibitor, emission factors, drip irrigation, semiarid wheat, IPCC Tier 1, greenhouse gas mitigation, nitrogen fertilizer, Morocco, soil microbiology