DMPP, short for 3,4-dimethylpyrazole phosphate, is a nitrification inhibitor, a compound that slows the microbial oxidation of ammonium into nitrate. By keeping nitrogen in its ammonium form for longer, DMPP is meant to synchronize nutrient supply with crop demand. But while the chemistry of inhibition is well understood, the biological consequences for the crop have been murkier. Researchers led by Wenbin Deng, Zhenfeng Miao and colleagues at the Institute of Soil Science of the Chinese Academy of Sciences and Nanjing Forestry University set out to close that gap, asking a deceptively simple question: when DMPP changes the form of nitrogen available in the soil, how does the cotton root respond, and does that response translate into more fiber on the plant?

To answer it, the team ran a two-pronged investigation. The first component was a controlled pot experiment comparing cotton grown with urea alone against cotton grown with urea plus DMPP, under both low and moderate soil salinity. The second was a two-year field validation across the 2024 and 2025 growing seasons in a drip-irrigated cotton system, the standard production setup for saline cotton land. This combination mattered, because pot experiments can reveal mechanisms with precision but often exaggerate effects, while field trials provide the reality check that farmers and agronomists need. Measuring the same variables across both scales gave the researchers confidence that what they observed in pots was not an artifact of container growing.

The core of the study lies in the biochemistry of nitrogen assimilation inside the root. Plants absorb nitrogen either as ammonium or nitrate, and then funnel it into amino acids through two main enzymatic pathways. Glutamine synthetase, or GS, works with glutamate synthase in the primary assimilation route, efficiently incorporating ammonium into organic molecules. Glutamate dehydrogenase, or GDH, acts more as a backup and recycling pathway, and is often associated with stress and ammonium detoxification. The researchers tracked the ratio of GS to GDH activity as an indicator of which pathway dominated. Under DMPP treatment, that ratio rose significantly, signaling a shift toward the more efficient GS-driven assimilation route, a change consistent with the plant receiving a steadier supply of ammonium rather than a flood of nitrate.

The internal nitrogen pools shifted accordingly. Roots treated with DMPP tended to accumulate more ammonium, while their nitrate content declined, exactly what one would expect when nitrification is suppressed in the rhizosphere. But the most striking results concerned root morphology and exudation. Roots are not passive sponges; they actively sculpt their shape and leak organic compounds into the surrounding soil to recruit beneficial microbes and mobilize nutrients. In the DMPP-treated plants, root morphological traits improved consistently, and the exudation of organic carbon, organic acids and soluble sugars all trended upward. In other words, changing the chemistry of nitrogen input did not just feed the plant differently; it changed how the root behaved as an organ, potentially altering the microbial communities that live around it.

These physiological changes had measurable consequences for yield. In the pot experiment, seed cotton yield rose significantly by 12 to 22 percent under DMPP, accompanied by higher total nitrogen uptake per plant. Interestingly, nitrogen-use efficiency, calculated as seed cotton yield divided by plant nitrogen content, remained similar between the urea-only and urea-plus-DMPP treatments. That distinction is important: DMPP did not make the plant squeeze more fiber out of every unit of nitrogen it absorbed, but it did help the plant absorb more nitrogen overall, likely by reducing losses from the soil and extending the window during which ammonium was available. The extra nitrogen taken up was then converted into extra yield.

The field validation added nuance that pot experiments alone could never provide. Under moderate salinity, the DMPP treatment significantly increased seed cotton yield, partial factor productivity and agronomic efficiency, the last two being standard agronomic indicators of how effectively fertilizer translates into harvestable product. Under low salinity, however, the differences were not statistically significant. This salinity-dependent pattern makes agronomic sense. In moderately saline soils, nitrification dynamics and root stress are more pronounced, so slowing nitrification and easing the root’s nitrogen-processing burden delivers a bigger payoff. In mildly saline soils, the baseline conditions are already less limiting, leaving less room for the inhibitor to make a difference. For farmers, the practical message is that DMPP is most valuable precisely where salinity stress is meaningful but not extreme.

To move beyond correlations, the researchers deployed two statistical tools that are increasingly common in plant science. Redundancy analysis, a multivariate method, was used to relate the suite of measured root variables to yield outcomes, while partial least squares structural equation modeling, or PLS-SEM, allowed the team to test hypothesized networks of cause and effect among latent variables. Both approaches supported a coherent picture: root nitrogen forms, the activities of assimilation enzymes, root morphological traits and root exudation were coordinated with one another and jointly associated with seed cotton yield. Rather than a single magic mechanism, DMPP appears to act through an integrated cascade, altering nitrogen chemistry in the soil, which reshapes root metabolism and architecture, which in turn supports yield formation.

The implications extend beyond cotton. Saline soils cover hundreds of millions of hectares worldwide, and as freshwater scarcity pushes agriculture toward marginal land, the question of how to fertilize salt-affected crops efficiently becomes ever more urgent. Nitrification inhibitors are already used to cut nitrous oxide emissions and nitrate leaching in maize and wheat systems, but this study is among the most detailed examinations of how they interact with the root physiology of a salt-stressed cash crop. The finding that DMPP shifts the GS/GDH balance and stimulates root exudation hints at broader ecological effects, since exuded sugars and organic acids feed the soil food web. Whether those exudation changes recruit microbes that further benefit the plant remains an open question for future research.

Caveats remain, as they always do. The field component spanned two years at sites within a single production system, and salinity in drip-irrigated fields is spatially patchy, so results may vary across regions with different soil types, climates and water quality. The authors also note that the published version was shared early as an accepted manuscript, subject to final editorial revision. Still, the work provides a concrete, evidence-based reference point for nitrogen management in drip-irrigated cotton under low to moderate salinity. For a crop that anchors rural economies across the arid and semi-arid world, a fertilizer additive that quietly reprograms the root to assimilate nitrogen more efficiently, grow more vigorously and exude more carbon could be a meaningful step toward sustainable intensification of salt-affected farmland.

Subject of Research: Effects of the nitrification inhibitor DMPP on cotton root nitrogen assimilation, morphology, exudation and yield under soil salinity

Article Title: DMPP alters cotton root nitrogen assimilation, morphology and exudation under salinity: evidence from pot and two-year field experiments

Article References: Deng, W., Miao, Z., Xie, H., Wang, X., Liu, G., Yao, R., & Chen, J. (2026). DMPP alters cotton root nitrogen assimilation, morphology and exudation under salinity: evidence from pot and two-year field experiments. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10126-3

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10126-3

Keywords: cotton, DMPP, nitrification inhibitor, soil salinity, nitrogen assimilation, GS/GDH ratio, root exudation, drip irrigation, seed cotton yield, nitrogen-use efficiency, root morphology, BMC Plant Biology