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

The findings, published in the Journal of Agriculture and Food Research, carry serious implications for how growers interpret soil tests, not just in Florida but anywhere crops are grown on phosphorus-enriched soils. Florida’s potato industry is substantial, with roughly 6,800 hectares harvested in 2023 producing 190,500 megagrams of tubers valued at 105.4 million dollars. Because potato plants have shallow root systems, limited root hairs, and a notoriously weak ability to scavenge phosphorus from soil, the crop is heavily dependent on fertilizer inputs. Decades of repeated applications have left many fields with elevated soil-test phosphorus values, well above the thresholds where guidelines say no additional fertilizer is needed.

Yet growers in the region have repeatedly reported yield losses when they withheld phosphorus in high-testing soils. To investigate, the research team ran a factorial experiment over three growing seasons at the UF/IFAS Hastings Agricultural Extension Center. Two adjacent 0.3-hectare sites were planted with the chipping cultivar Atlantic each spring from 2023 to 2025. The sites shared a soil type, a sandy Alfisol of the Ellzey series, but differed sharply in their starting phosphorus status. Site 1 averaged 50.6 milligrams per kilogram of Mehlich-1 extractable phosphorus in the surface 15 centimeters, while site 2 averaged 110.9 milligrams per kilogram. Under the historical interpretation system, both values fall into the high or very high categories, which normally trigger no phosphorus recommendation at all.

Each site received ten treatment combinations: five phosphorus pentoxide rates, from zero up to 269 kilograms per hectare, crossed with two nitrogen rates of 168 and 280 kilograms per hectare. The team tracked soil phosphorus and mineral nitrogen through the profile, measured plant biomass and nutrient uptake at 50, 70, and 90 days after planting, and mechanically harvested and graded tubers according to USDA size classes. A total of 240 plot-level observations across six site-years fed into the analysis.

The results were striking. At site 1, the field with the lower starting phosphorus, fertilization raised total yield from 21.6 megagrams per hectare in the unfertilized control to an average of 30.6 megagrams across rates of 135 to 269 kilograms of phosphorus pentoxide per hectare, a gain of roughly 42 percent. Marketable yield climbed even more dramatically, from 16.4 to about 25.1 megagrams per hectare, an increase of 53 percent. Most of the gain came from intermediate-sized tubers, the A23 fraction, which jumped from 9.1 to 17.4 megagrams per hectare. Tuber specific gravity, a key quality measure for chipping potatoes, also improved. At site 2, by contrast, phosphorus rate had no significant effect on total yield, marketable yield, tuber size distribution, or specific gravity, and the yield gap between the two sites vanished once phosphorus was applied at 135 kilograms per hectare or more.

The physiological story behind those numbers is revealing. At site 1, phosphorus fertilization increased whole-plant dry biomass from 5.48 to 7.96 megagrams per hectare and nitrogen uptake from 89.5 to 132.2 kilograms per hectare, while nitrogen uptake efficiency rose from 26.8 to 42.3 percent. In other words, when phosphorus is limiting, the constraint ripples outward: restricted root and shoot growth lower the plant’s demand for nitrogen and its capacity to acquire it. Adequate phosphorus supply therefore unlocks the crop’s ability to use nitrogen efficiently. At site 2, the higher-phosphorus field, the only response to added fertilizer was a modest increase in nitrogen uptake efficiency, with biomass and productivity per unit of nitrogen unchanged. Notably, whole-plant phosphorus uptake at site 2 pulled ahead of site 1 after 50 days after planting and stayed ahead through harvest, showing that the richer soil sustained phosphorus delivery during the critical tuber-bulking period.

Nitrogen management, meanwhile, turned out to be a non-player in the phosphorus story. The two nitrogen rates produced clearly different soil mineral nitrogen levels, but phosphorus rate by nitrogen rate interactions were limited to efficiency indices, and the crop’s principal responses to phosphorus were identical under both nitrogen regimes. Raising nitrogen from 168 to 280 kilograms per hectare never increased yield and consistently reduced both nitrogen uptake efficiency and partial factor productivity, the tubers produced per kilogram of nitrogen applied. In the difficult 2024 season, when seed-piece decay cut plant stands by 57 percent, the higher nitrogen rate actually lowered total and marketable yields by about 4.4 megagrams per hectare. The team stresses this does not establish 168 kilograms as a regional optimum, only that extra nitrogen neither overcame phosphorus deficiency nor added yield when phosphorus was sufficient.

The soil itself told a story of accumulation and movement. Over the experiment, surface Mehlich-1 phosphorus in fertilized plots rose by roughly 63 to 67 milligrams per kilogram, while unfertilized controls declined by 7 to 27. Concentrations peaked near crop emergence after pre-plant fertilization and then shifted, with measurable increases detectable down to the 30 to 45 centimeter layer, particularly at site 2 in 2024. Because most potato roots in these seepage-irrigated soils sit within the top 30 centimeters, phosphorus moving below that depth is effectively out of reach for the crop and represents a potential pathway for transport off-site, although drainage losses were not directly measured in this study.

To translate the yield responses into a usable threshold, the researchers modeled relative yield against Mehlich-1 phosphorus measured at harvest using four normalization methods and several calibration models. The best-performing combination, the MAXRATE normalization paired with a modified arcsine-log model, explained 41 percent of the variation in relative yield. It estimated critical phosphorus levels of 63.6 milligrams per kilogram for 80 percent relative yield, 81.4 for 90 percent, and 96.2 for 95 percent, with the response curve flattening above roughly 100 milligrams per kilogram. Those numbers are far above the historical sufficiency threshold of about 30 milligrams per kilogram of Mehlich-1 phosphorus, and they even exceed the high category boundaries of both the Mehlich-1 and Mehlich-3 systems currently used in Florida. The moderate fit and the overlap of high- and low-yielding observations across the range reinforce a point echoed in decades of Ohio fertilizer trials: a soil test is a probabilistic index of potentially available phosphorus, not a deterministic boundary between deficiency and sufficiency.

The practical message is nuanced. A high soil-test classification does not guarantee a field will ignore added phosphorus, and skipping fertilizer in a responsive high-testing soil can be costly; conversely, blanket phosphorus applications to nonresponsive soils simply inflate soil phosphorus reserves and environmental risk. The authors caution that their critical level of 96.2 milligrams per kilogram derives from a specific soil, cultivar, sampling protocol, and set of conditions, and that each initial phosphorus status was represented by a single site with different irrigation infrastructure, so broader calibration and independent validation are needed before any new threshold enters recommendations. Still, the study makes a compelling case that Florida’s provisional allowance of up to 134 kilograms of phosphorus pentoxide per hectare, applied regardless of soil test, is a blunt instrument. A validated critical level could enable a tiered strategy: full fertilization below the threshold, crop-removal-based maintenance near it, and deliberate drawdown above it, protecting both potato yields and the waterways downstream of phosphorus-enriched sands.

Subject of Research: Potato yield and nutrient uptake responses to phosphorus fertilization in phosphorus-enriched sandy soils

Article Title: Initial soil phosphorus status governs potato yield and nutrient uptake responses to fertilization in P-enriched sandy soils

Article References: Oliveira, J. D. M., de Castro, G. F., da Silva, B. A., Clark, M. W., Nunez, G. H., Guzmán, S., & Zotarelli, L. (2026). Initial soil phosphorus status governs potato yield and nutrient uptake responses to fertilization in P-enriched sandy soils. Journal of Agriculture and Food Research, 31, Article 103296. https://doi.org/10.1016/j.jafr.2026.103296

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103296

Keywords: phosphorus, potato, soil testing, Mehlich-1, fertilizer recommendations, sandy soils, nitrogen use efficiency, critical phosphorus level, Florida agriculture, nutrient uptake, soil fertility, alfisols