Interactive effects of coffee husk biochar and NPSB rates on food barley (Hordeum vulgare L.) yield under limed and unlimed acidic soils

A field experiment was conducted in 2024 at Wacha Kebele, Chena District, southwestern Ethiopia, to evaluate the integrated effects of coffee husk biochar (CHB) and NPSB blended fertilizer on food barley under limed and unlimed acidic soil conditions. The treatments included three rates of NPSB fertilizer (50, 100, and 150 kg ha −1 ) and coffee husk biochar (2.5, 5, and 7.5 t ha −1 ), arranged in a randomized complete block design (RCBD). The combined application of CHB and NPSB significantly improved barley yield and profitability. The highest grain yield (4,150 kg ha −1 ) was obtained from the combined application of 100 kg ha −1 NPSB and 5 t ha −1 coffee husk biochar (CHB) under limed conditions, whereas the highest net benefit (210,585.6 ETB ha −1 ) and marginal rate of return (MRR; 5,785.33%) were also recorded with this treatment. Under unlimed conditions, the highest grain yield (3,119 kg ha −1 ) was obtained from 100 kg ha −1 NPSB + 7.5 t ha −1 CHB, which also produced the highest net benefit (157,520.3 ETB ha −1 ) and MRR (4,892.5%). These results indicate that the treatments maximizing grain yield coincided with the economically optimal treatments under both limed and unlimed conditions. Overall, the study demonstrates that integrating coffee husk biochar with NPSB fertilizer is an effective and economically viable strategy for improving food barley production in acidic soils. Based on agronomic and economic performance, the application of 100 kg ha −1 NPSB combined with 5 t ha −1 CHB under limed conditions is recommended for the study area and similar agroecologies. Further multi-location and multi-year studies are recommended to validate these findings and refine fertilizer recommendations.