A new field study conducted in Dhading, Nepal, and published in BMC Agriculture, offers some of the clearest evidence yet that the solution lies not in any single nutrient but in the interaction between two of them. Prabin Ghimire and Janma Jaya Gairhe, both of the Institute of Agriculture and Animal Science at Tribhuvan University, spent two consecutive growing seasons testing how nitrogen and boron, applied alone and in combination, shaped the yield, fertility, and soil chemistry of a wheat crop. Their central finding is striking: when the two nutrients were applied together at the right rates, grain yields climbed to levels far above the national average, and a persistent reproductive failure known as wheat sterility fell dramatically.

The problem the researchers set out to address is both agronomic and chemical. Nitrogen is the macronutrient that drives vegetative growth, tillering, and biomass accumulation in wheat, and decades of research have confirmed that raising nitrogen inputs generally raises grain yields. But the relationship is not linear. Excessive nitrogen can trigger diminishing returns, nutrient leaching, soil acidification, and lodging, the structural collapse of top-heavy plants. Boron, by contrast, is a micronutrient required in tiny amounts, but its role is outsized: it is essential for pollen viability and fertilization, and its deficiency is directly linked to spikelet sterility, the failure of flowers to set grain. In Nepal, boron-deficient soils are widespread and have long been associated with outbreaks of wheat sterility that slash harvests without any visible disease.

What has been missing, the authors argue, is field-scale evidence of how these two nutrients behave together, particularly in soils where both are deficient. Baseline analysis of the experimental site in Dhading, a monsoon-influenced humid subtropical location classified as a Dystric Loamic Fluvisol, revealed total nitrogen at just 0.14 percent and boron at 0.21 parts per million, both below the critical thresholds for optimal wheat growth. Government fertilizer recommendations in Nepal are typically issued for broad agroecological zones, with little allowance for site-specific soil chemistry, seasonal variability, or local climate. That gap leaves farmers applying nutrients in proportions that may be agronomically wrong for their fields, wasting money and degrading soil in the process.

To test the interaction directly, the team ran a split-plot experiment across the 2020 and 2021 cropping seasons using the medium-maturity wheat variety BL3063, obtained from Nepal’s National Wheat Research Program. Main plots received nitrogen at 0, 80, 100, or 120 kilograms per hectare, applied as urea in three splits: half incorporated before sowing, a quarter at 30 days after sowing, and a quarter at 60 days. Subplots received boron at 0, 1, or 2 kilograms per hectare as a basal dose. The design was replicated three times, and the researchers analyzed their results with linear mixed-effects models that treated year and replication as random effects, allowing them to separate genuine treatment effects from environmental noise. Grain yields were standardized to 14 percent moisture, and plant tissue nitrogen was measured by the micro-Kjeldahl method at three key phenological stages: tillering, booting, and grain filling.

The results were unambiguous. Nitrogen application significantly increased grain yield, biological yield, and straw yield, with the highest grain yield, 8,143.89 kilograms per hectare, recorded at 120 kilograms of nitrogen per hectare. That figure represents a 49.3 percent increase over the unfertilized control, which yielded 5,455.87 kilograms per hectare, and it dwarfs Nepal’s national average of roughly 2.99 tonnes per hectare. Tissue nitrogen concentrations rose consistently with application rate at every growth stage, peaking during tillering, which the authors interpret as confirmation of a clear dose-specific and phenological response. Boron, meanwhile, delivered its own kind of magic: applying it significantly reduced spikelet sterility and improved grain yield, with the effect visible in both seasons.

The most compelling numbers emerged from the interaction analysis. The lowest sterility rate, 33.2 percent, occurred under the combined treatment of 120 kilograms of nitrogen and 2 kilograms of boron per hectare, a 35.9 percent reduction compared with the control treatment, which suffered 51.8 percent sterility. Notably, the regression analysis revealed a consistent negative relationship between applied boron and sterility across both years, and the statistical groupings showed that even the moderate dose of 1 kilogram per hectare significantly outperformed the control. The authors attribute the synergy to boron’s role in nitrogen metabolism: the micronutrient facilitates nitrogen uptake, supports protein synthesis, and ensures effective pollen viability and fertilization, thereby maximizing grain set precisely when nitrogen availability is at its highest.

The soil story is more complicated, and it carries a warning. Post-harvest analysis of the top 20 centimeters of soil showed that increasing nitrogen rates significantly reduced soil pH, with the acidification effect more pronounced in 2021 than in 2020. This is consistent with the well-documented chemistry of nitrification, in which ammonium-based fertilizers release hydrogen ions as soil microbes convert ammonium to nitrate. Total soil nitrogen did increase with higher application rates, indicating a genuine fertility gain, and boron availability responded strongly to boron treatments, though with notable year-to-year variation likely driven by environmental factors. Phosphorus and potassium levels remained largely unchanged. The authors suggest that liming may be needed to counteract long-term acidification, and they emphasize that balanced fertilization, rather than nitrogen alone, is the key to maintaining soil health over time.

The study is not without limitations, and the authors are candid about them. Two growing seasons cannot capture the full arc of soil fertility dynamics or climate variability, and only one wheat variety was tested, leaving open the question of whether other genotypes would respond similarly. Sterility, moreover, can also be driven by temperature fluctuations and drought stress, for which site-specific data were not available. Still, the stability of the grain yield response across both years, and the absence of a significant three-way interaction between year, nitrogen, and boron, suggest that the underlying biology is robust. The practical implications are immediate: micronutrients like boron deserve a formal place in national fertilizer recommendations, not as an afterthought but as a co-equal partner to nitrogen. For a country striving toward wheat self-sufficiency, the path forward may run through a nutrient most farmers have never measured, applied at rates measured in single kilograms rather than hundreds, working quietly in the pollen tubes of every wheat flower to turn nitrogen into grain.

Subject of Research: Interactive effects of nitrogen and boron fertilization on wheat yield, spikelet sterility, and soil fertility in Nepal

Article Title: Nitrogen-boron in wheat: yield optimization and soil fertility in Nepal

Article References: Ghimire, P., & Gairhe, J. J. (2025). Nitrogen-boron in wheat: yield optimization and soil fertility in Nepal. BMC Agriculture, 1(1), Article 11. https://doi.org/10.1186/s44399-025-00014-w

Image Credits: AI Generated

DOI: 10.1186/s44399-025-00014-w

Keywords: wheat, nitrogen, boron, spikelet sterility, soil fertility, soil acidification, nutrient management, fertilizer recommendations, Nepal, agronomy, crop yield, micronutrients