Integrated nitrogen and NPSB fertilization enhances productivity, nutrient-use efficiency, and profitability of tef (Eragrostis tef (Zucc.) Trotter) in Southwestern Ethiopia

The field experiment was carried out during the 2022 main cropping season under rainfed conditions on a farmer’s field in Gechi District, southwestern Ethiopia. The objective was to evaluate the effects of different rates of N combined with NPSB fertilizer on the growth, yield, and yield components of tef varieties, and to identify the economically optimum fertilizer rate for maximizing tef production under the local conditions. A factorial experiment comprising three tef varieties and six nitrogen–NPSB fertilizer combinations (3 × 6) was conducted using a randomized complete block design with three replications. Except for days to 50% flowering (DF), days to 90% physiological maturity (DPM), and harvest index (HI), both the main effects and the interaction effects of variety and fertilizer rate significantly ( p < 0.05) influenced all measured parameters. The interaction of tef variety and fertilizer rate significantly ( p < 0.05) affected grain yield, thousand-seed weight, harvest index, and net benefit. Based on the present study, the Kora variety supplied with 34.5 kg N + 200 kg NPSB ha⁻ 1 achieved the highest grain yield (2565.4 kg ha⁻ 1 ), representing approximately a 162% increase over the unfertilized control and a 40% increase over the currently recommended fertilizer treatment, together with the greatest net economic return. Although the Kora variety supplied with 34.5 kg N + 200 kg NPSB ha⁻ 1 produced the highest grain yield, agronomic efficiency, and economic return under the conditions of this study, these findings are based on a single-location, single-season experiment. Therefore, the recommendation should be considered preliminary and applicable primarily to agroecological conditions similar to those of Gechi District until validated through multi-location and multi-season experiments.