Response of Npk 15-15-15 on the Performance of African Yam Beans (sphenostylis Stenocarpa) at The vegetative Stage

African yam bean (AYB) is an underutilized leguminous crop with significant nutritional and agronomic potential in tropical regions where soil fertility challenges limit crop productivity. Despite its inherent benefits, AYB is underexploited due to inadequate nutrient management practices that lead to suboptimal growth and yield. Therefore, the study addresses the problem of nutrient deficiency in AYB cultivation by investigating the effects of NPK 15-15-15 fertilizer application on early vegetative growth. A 2×4 factorial experiment was conducted using two AYB accessions (TSS10 and TSS67) and four fertilizer rates (0, 50, 100, and 200 kg ha⁻¹) arranged in a randomized complete block design. This was carried out at the Teaching and Research Farm, Ekiti State University, Nigeria, with soil physiochemical properties characterised before experimentation. The growth parameters measured are vine length, number of leaves per plant, and stem girth. Data were analysed using analysis of variance (ANOVA) to determine the significance of treatment effects and their interactions. Findings show that NPK application significantly enhanced vegetative growth in terms of stem girth and leaf production at later growth stages (8 weeks after planting). Notably, optimal responses were observed at fertilizer rates of 100–200 kg ha⁻¹, though the degree of responsiveness varied between accessions, with TSS67 exhibiting greater sensitivity to nutrient enrichment than TSS10. Analysis of variance revealed significant effects of fertilizer levels, variety, and their interactions on growth performance, with several treatment effects reaching statistical significance at both the 5%* and 1%** levels. In conclusion, the targeted NPK 15-15-15 application is a viable strategy for enhancing the early growth and long-term productivity of AYB.