Site-specific nitrogen optimization for enhanced productivity and economic returns of sesame (Sesamum indicum L. cv. Ex-Sudan) under rainfed conditions in the Sudan Savannah agroecological zone of Northern Nigeria

Abstract Inadequate nutrient management, particularly nitrogen fertilization is a primary driver of yield gaps in sesame ( Sesamum indicum L.) production across Nigeria’s Sudan Savannah. Field experiments using a randomized complete block design with seven nitrogen rates (0–120 kg N ha⁻¹) were conducted on farmers’ fields in Dambatta (Kano State) and Dutse (Jigawa State) during the 2024 rainy season. Data on soil properties, weather, agronomic traits, tissue nutrient status, and economic returns were collected. Nitrogen application significantly ( p < 0.05) affected growth parameters (plant height, branching, leaf area index, and flowering), yield components, seed yield, oil content, Nitrogen Use Efficiency, and economic returns. The agronomic optimum nitrogen rate (AONR) was 106.9 kg N ha⁻¹ in Dambatta and 90.0 kg N ha⁻¹ in Dutse, producing yields of 1,041.5 and 946.6 kg ha⁻¹, respectively. Quadratic models explained 97.9% and 98.9% of yield variation in Dambatta and Dutse, respectively. Economic optimum nitrogen rate (EONR) analysis identified 80 kg N ha⁻¹ as the most profitable rate based on marginal returns and benefit–cost ratio, although maximum net revenue in Dambatta occurred at 100 kg N ha⁻¹ ($608.43 ha⁻¹; BCR = 4.97). Dutse also had EONR at 80 kg N ha⁻¹ with a return of $583.68 ha⁻¹ with a BCR of 4.81. Agronomic Efficiency (AE) exhibited an inverse relationship with application rates, declining from 15.2 to 8.7 kg grain kg⁻¹ N in Dambatta and 13.8 to 7.2 in Dutse. Leaf nitrogen content correlated positively with seed yield ( r = 0.558, p < 0.001). Site-specific nitrogen management is therefore crucial to enhance sesame productivity, profitability, and food security in the region.