Poor agronomic management such as nutrient management and plant density are critical challenges of lentil production in Ethiopia. Therefore, this study was conducted to determine the effects of different row spacing and phosphorus (P) applications on the seed yield of lentil at Ude and Minjar, in 2017 up to 2019. The experiment was conducted in completely randomized block design with three replications. The treatments were comprised of a factorial arrangement of three levels of row spacing (20, 30 and 40 cm) and four levels of P fertilizer (0, 30, 60 and 90 kg P2O5 ha-1). The result revealed that at Ude, the row spacing x P fertilizer interactions was a significant effect on the biomass, seed, and haulm yield of lentil. However, at Minjar; only the main effects of row spacing and P fertilizer had a significant effect on biomass, seed, and haulm yield. Phosphorus agronomic use efficiency was significantly influenced by the interaction of row spacing and P fertilizer. As a result, the highest phosphorus agronomic use efficiency was recorded at 30 kg P2O5 ha-1coupled with 20 cm row spacing at both locations. The economic analysis revealed that 20 cm row spacing and 30 kg P2O5 ha-1fertilizer managements gave the highest net benefit and acceptable marginal rate of return (MRR) as compared to other practices at both locations. Therefore, 20 cm row spacing and 30 kg P2O5 ha-1rate of fertilizer would be recommended to enhance the productivity of lentil in the study areas.

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