Optimizing soil fertility, malt barley yield, and economic returns through integrated compost and nitrogen fertilization: yield, soil, and economic analysis in the Ethiopian highlands

Malt barley is an important crop in the Ethiopian highlands, where productivity is challenged by soil fertility decline, inappropriate agronomic practices, and high dependence on inorganic fertilizers. This study evaluated the effects of compost and inorganic N fertilizer application on yield and yield components, soil chemical properties, and economic returns of malt barley during the 2022 and 2023 growing seasons in the central highlands of Ethiopia. The trial was arranged in a randomized complete block design with factorial combinations of five N rates (0, 23, 46, 69, and 92 kg N ha^-1) and four compost rates (0, 2.5, 5, and 7.5 t ha^-1), with three replications. The results showed that integrated application of organic compost and mineral N fertilizer significantly increased yield and yield components, and improved selected post-harvest soil chemical properties, including soil pH, available phosphorus, total nitrogen, total organic carbon, organic matter, and cation exchange capacity, compared with the control treatment. The combined application of compost and mineral nitrogen fertilizer significantly increased days to 50% heading, plant height, seeds per spike, above-ground biomass yield, straw yield, and harvest index, and grain yield compared with the control treatment. The 2023 growing season increased plant height, seeds per spike, grain yield and above-ground biomass yield, and total nitrogen content and available phosphorus, while the 2022 growing season delayed phenological parameters such as days to 50% heading and days to 90% physiological maturity and suppressed overall productivity, demonstrating that seasonal conditions strongly affected treatment performance. However, integrated application of compost and mineral nitrogen fertilization consistently improved malt barley productivity across both growing seasons. The highest grain yield value (3856.59 kg ha^-1) was obtained from the application of 7.5 t compost ha^-1 + 92 kg N ha^-1 of fertilizer rates, showing a 143% yield advantage over control and a 24% increase over sole mineral N application. The economic analysis identified the combination of 7.5 t ha^-1 compost with 69 kg N ha^-1 fertilizer as economically advantageous, giving the highest net benefit and marginal rate of return. Overall, integrated nutrient management significantly enhanced malt barley productivity, selected soil chemical properties, and economic returns within the conditions of the current study. However, the results are limited by a single site over two growing seasons, lack of long-term soil assessments, and reliance on local market prices for economic analysis.