Food barley serves as a vital dietary staple and key source of agricultural income across high-altitude farming regions in Ethiopia. However, regional crop productivity remains severely constrained by acidic soil dynamics, continuous cultivation without adequate nutrient replenishment, and high rates of rainfall-induced nutrient leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More. Traditional liming protocols help neutralize ground acidity, but elevated material costs and ongoing soil organic matter depletion limit long-term effectiveness when used in isolation. To develop a more resilient soil management alternative, researchers established field experiments in southwestern Ethiopia to evaluate how coffee husk biochar interacts with blended mineral fertilizers under both limed and unlimed soil conditions.

Field trials revealed that integrating coffee husk biochar with NPSB blended fertilizer dramatically improved crop growth parameters and overall harvest output compared to unamended control plots. Under limed soil conditions, combining five tons per hectare of coffee husk biochar with one hundred kilograms per hectare of NPSB fertilizer produced the maximum grain yield of four thousand one hundred fifty kilograms per hectare. This treatment represented a three hundred seventy-six point five percent increase over untreated control plots, which yielded only eight hundred seventy-one kilograms per hectare. Under unlimed conditions, applying seven point five tons of biochar with one hundred kilograms of NPSB fertilizer produced three thousand one hundred nineteen kilograms per hectare, reflecting a three hundred forty-eight percent yield increase over unlimed controls.

The clear yield gap between limed and unlimed trial sets highlighted the underlying mechanics of acidity correction and nutrient availability. Comparing peak performance across both management systems demonstrated that lime application enhanced top grain yield by one thousand thirty-one kilograms per hectare, representing a thirty-three point one percent increase over the best unlimed treatment. Liming neutralized ground acidity, suppressed exchangeable aluminum toxicity, and boosted the plant availability of essential nutrients such as phosphorus, nitrogen, and calcium. Simultaneously, the alkaline coffee husk biochar improved soil water retention, elevated cation exchange capacity, and expanded productive tiller density from one hundred four tillers per square meter in controls to four hundred thirty-eight tillers per square meter.

Economic evaluations confirmed that agronomic gains translated directly into maximum farm profitability. Partial budget and marginal rate of return analyses established that applying five tons per hectare of coffee husk biochar with one hundred kilograms of NPSB fertilizer under limed conditions generated the highest net financial benefit of two hundred ten thousand five hundred eighty-five point six Ethiopian Birr per hectare. This specific management combination achieved an extraordinary marginal rate of return of five thousand seven hundred eighty-five point thirty-three percent, vastly exceeding standard economic viability thresholds. These findings confirm that combining local coffee waste biochar with balanced mineral fertilizers provides a highly effective, circular strategy for restoring acidic soils and securing cereal production.

Source: Zewide, I., Tamiru, T., & Wato, T. (2026). Interactive effects of coffee husk biochar and NPSB rates on food barley (Hordeum vulgare L.) yield under limed and unlimed acidic soils. Scientific Reports, 16, 67517.