This study aimed to determine the optimum nitrogen (N) and phosphorus (P) requirements for Tef (Eragrostis tef) production in Yabello District, Southern Oromia, Ethiopia, where soil phosphorus deficiencies often limit crop yields. The experiment was conducted over two phases during the 2022-2024 cropping seasons. In the first phase, 12 factorial treatments combining four nitrogen levels (0, 46, 69, 92 kg/ha) and three phosphorus levels (0, 30, 40 kg/ha) were tested to identify the optimal nitrogen rate. In the second phase, 46 kg N/ha was applied uniformly, and six phosphorus levels (0, 10, 20, 30, 40, 50 kg/ha) were tested to determine the phosphorus critical (Pc) level and phosphorus requirement factor (Pf). The experiment followed a randomized complete block design (RCBD) with three replications. The results showed that grain yield was significantly influenced by the interaction of nitrogen and phosphorus rates. The highest grain yield (1748.23 kg/ha) occurred with 40 kg P/ha and 46 kg N/ha. Economic analysis revealed the highest net benefit (103,603 Birr/ha) and a marginal rate of return of 543% with 46 kg N/ha and 40 kg TSP/ha. The determined phosphorus critical level (Pc) was 14 ppm, and the phosphorus requirement factor (Pf) was 5.79. Based on these findings, the recommended optimal nitrogen rate is 46 kg N/ha, with a Pc of 14 ppm and a Pf of 5.79 for Tef production in Yabello and similar agro-ecological areas. Verification on additional farmland may be necessary before full technology distribution.