A Fertilizer Formula Nearly Doubled Wheat Yields in Ethiopia’s Northwestern Highlands
A carefully calibrated fertilizer combination has more than doubled bread wheat yields in parts of Ethiopia’s northwestern highlands, according to a field study conducted in the Debark and Wogera districts of the Amhara Region. The researchers found that applying 161 kilograms of nitrogen per hectare together with 46 kilograms of phosphorus pentoxide per hectare produced the strongest overall balance of yield, plant growth and farm profitability. Wheat grain production reached 4,952 kilograms per hectare under the optimal nitrogen treatment, compared with 2,196 kilograms per hectare in unfertilized plots—an increase of 125.5 percent. The result points to a surprisingly specific agricultural lever in a region where farmers often rely on uniform fertilizer recommendations that may not match local soil conditions.
The finding matters because wheat is central to Ethiopia’s food system, yet national yields remain below the global average. The crop supplies much of the country’s dietary energy, while its straw is also valuable as livestock feed. In the highlands, however, years of cultivation, erosion and nutrient removal have contributed to declining soil fertility. Nitrogen and phosphorus are both essential for plant development, but they do not play identical roles. Nitrogen is a core component of chlorophyll, amino acids, proteins and many enzymes, allowing plants to capture light and convert it into biomass. Phosphorus is involved in energy transfer, nucleic acids, membrane formation and root development. Supplying either nutrient in excess can waste money or create environmental problems, while supplying too little can limit the crop’s response to other inputs.
To test how the two nutrients interacted, Melkamu Adane Mulat of the Gondar Agricultural Research Center and colleagues established experiments during the 2023–24 main rainy season. They grew the Alidoro bread wheat variety in two farmers’ fields, using a randomized complete block design with three replications. The trial compared four nitrogen rates—115, 161, 207 and 253 kilograms per hectare—with three phosphorus rates of 46, 69 and 92 kilograms of P₂O₅ per hectare. A completely unfertilized control was included for comparison, producing 13 treatments in total. Nitrogen was supplied as urea and divided into three applications, with one-third applied at planting, one-third during tillering and the final portion at booting. Phosphorus, supplied as triple superphosphate, was applied entirely at planting.
The study sites sit at elevations of roughly 2,750 to 2,800 meters above sea level, where cool, moist highland conditions support wheat cultivation during the rainy season. Average annual rainfall over the previous decade was about 1,019 millimeters at Debark and 1,185 millimeters at Wogera. The soils were classified primarily as Cambisols, with clay-loam texture at Wogera and clay texture at Debark. Laboratory tests showed slightly acidic soils with moderate organic carbon and total nitrogen, medium available phosphorus and high cation-exchange capacity. Cation-exchange capacity is a measure of how effectively soil can retain positively charged nutrient ions, including ammonium, potassium and calcium. These characteristics make the soils broadly suitable for wheat, but the moderate nutrient status means that crop demand can still exceed the supply available from the soil alone.
Nitrogen had the clearest influence on grain production. Yields rose from 4,590 kilograms per hectare at 115 kilograms of nitrogen to 4,952 kilograms per hectare at 161 kilograms of nitrogen, a 7.88 percent increase between those two rates. But adding more nitrogen did not continue the upward trend. Grain yield declined at 207 and 253 kilograms per hectare, demonstrating the classic agricultural principle of diminishing returns. At moderate rates, nitrogen stimulates leaf expansion, tiller formation and photosynthesis, while also supporting the transfer of carbohydrates and proteins into developing grains. Beyond the crop’s optimum, additional nitrogen can promote excessive vegetative growth, increase lodging and disease risk, disrupt nutrient balance or leave more nitrogen vulnerable to loss through leaching and gaseous emissions.
A statistical model reinforced that interpretation. The researchers reported a positive linear nitrogen term of 28.83 and a negative quadratic term of −0.073, indicating that yield initially increased with nitrogen but eventually fell. The model explained 96.2 percent of the observed variation in grain yield, although the study’s experimental scale and limited number of locations mean the equation should not be treated as a universal fertilizer calculator. Its estimated biological optimum was approximately 198 kilograms of nitrogen per hectare, whereas the field treatment that delivered the highest measured grain yield was 161 kilograms per hectare. That difference highlights an important distinction between a mathematical yield maximum and a practical recommendation: farmers must also consider fertilizer prices, crop value, weather uncertainty, risk and the efficiency with which plants convert nutrients into harvestable grain.
Phosphorus produced a weaker direct response in grain yield, apparently because the soils already contained moderate amounts of plant-available phosphorus. The nutrient was not found to significantly affect grain yield by itself, nor did its interaction with nitrogen significantly alter grain yield. It did, however, influence crop structure in combination with nitrogen. The greatest number of effective tillers—4.62 per plant—was recorded with 161 kilograms of nitrogen and 69 kilograms of P₂O₅ per hectare. Effective tillers are stems that survive to produce grain-bearing spikes, so their number can strongly affect yield potential. Phosphorus supports root growth and energy metabolism, which may improve nitrogen acquisition and help more tillers develop into productive stems even when the final grain-yield response is modest.
The clearest combined effect appeared in aboveground biomass. The highest dry biomass yield, 14.98 tonnes per hectare, came from 161 kilograms of nitrogen plus 46 kilograms of P₂O₅ per hectare, compared with 6.19 tonnes per hectare in the control. Biomass includes grain, straw, stems, leaves and other aboveground plant material, making it important not only for crop production but also for livestock feed in mixed farming systems. Applying more than the recommended combination did not significantly improve biomass and in some cases produced a yield penalty. The result suggests that phosphorus may have an important supporting and soil-fertility role even where nitrogen is the nutrient most directly limiting wheat grain production.
The economic analysis made the recommendation more compelling. Using local prices for grain, straw, fertilizer, labor and transport, the researchers adjusted experimental yields downward by 10 percent to account for the advantages of small research plots and unusually careful management. The treatment combining 161 kilograms of nitrogen with 46 kilograms of P₂O₅ per hectare generated the highest estimated net benefit: 313,460 Ethiopian birr per hectare. Its marginal rate of return was 660 percent, meaning the additional investment in the treatment produced a substantial return above the added variable cost. Other economically viable combinations included 115 kilograms of nitrogen with 69 kilograms of P₂O₅, which generated a net benefit of 295,061 birr per hectare and a 760 percent marginal return, and 115 kilograms of nitrogen with 46 kilograms of P₂O₅, which produced 284,437 birr per hectare and a 1,060 percent marginal return. The researchers nevertheless identified 161/46 as the best overall compromise between biological performance and financial gain.
The study also revealed why simply applying more fertilizer is not synonymous with farming more efficiently. Nitrogen agronomic efficiency—the additional grain produced per kilogram of nitrogen applied—was highest at 115 kilograms of nitrogen per hectare, reaching 20.92 kilograms of grain per kilogram of nitrogen. It fell to 10.54 kilograms per kilogram at the highest nitrogen rate tested. In other words, the 161-kilogram rate maximized grain yield and profit in this experiment, but the lower rate converted each unit of fertilizer more efficiently. Nitrogen uptake followed a similar biological pattern: grain nitrogen uptake peaked at 130.06 kilograms per hectare with 161 kilograms of applied nitrogen, while straw nitrogen uptake reached 46.35 kilograms per hectare at 207 kilograms of nitrogen. Much of the nitrogen absorbed by the plant was concentrated in the grain, consistent with the movement of nitrogen into protein-rich reproductive tissues during grain filling.
The findings are not a license to copy one fertilizer formula across every Ethiopian farm. Soil nutrient levels vary sharply across landscapes, and rainfall distribution, previous crops, wheat variety, planting date and fertilizer prices can all change the economic optimum. The researchers’ recommendation is specifically aimed at the Cambisol-based agro-ecologies of Debark, Wogera and similar highland environments. They also emphasize the need for longer-term research, particularly because repeated high nitrogen use can contribute to soil acidification, nutrient imbalance and nitrogen losses to water and the atmosphere. Still, the field evidence delivers a powerful message for food security: when fertilizer is matched to the nutrient that is genuinely limiting, a relatively modest adjustment in management can transform wheat production. In these Ethiopian highlands, the winning strategy was not simply more fertilizer, but the right amount of nitrogen paired with enough phosphorus to support the crop and the soil.
Subject of Research: Nitrogen and phosphorus fertilizer optimization for bread wheat production in the Northwestern Ethiopian highlands
Article Title: Optimal nitrogen and phosphorus fertilizer rates for bread wheat production in the Northwestern Ethiopian highlands
Article References: Mulat, M. A., Tiruneh, K. J. & Endalew, B. A. “Optimal nitrogen and phosphorus fertilizer rates for bread wheat production in the Northwestern Ethiopian highlands.” Discover Agriculture 4, Article 223 (2026). Original research article
Image Credits: AI Generated
DOI: 10.1007/s44279-026-00692-3
Keywords: bread wheat, nitrogen fertilizer, phosphorus fertilizer, Ethiopia, grain yield, Cambisol soils, agronomic efficiency, smallholder farming, fertilizer economics
Tags: agricultural practices in Northwestern Ethiopiabread wheat yield improvementcrop yield enhancement strategiesEthiopian highlands agriculturefertilizer application rates for bread wheatfood security through improved wheat yieldshigh-yield wheat farming techniquesimpact of fertilizer on wheat yieldsnitrogen and phosphorus fertilizer optimizationregional fertilizer recommendations for Ethiopiasoil fertility management in Ethiopiasustainable wheat production in Ethiopia
