Complementary Application of NPK 15.15.15 Fertilizer with Different Source of Ash Materials on the Soil Properties, Nutritional Composition and Yield Performance of Ipomoea batatas

The research trial was to evaluate the complimentary effects of NPK 15.15.15 with different source of ash materials on the soil chemical properties, proximate content, growth and yield of sweet potato.The field trial was arranged using randomized complete block design (RCBD) with five (5) different treatments: NPK at 400 kg/ha, NPK at 200 kg/ha + dried mango leave ash, NPK at 200 kg/ha + rice husk dust, NPK at 200 kg/ha + wood ash, and control (no fertilization) replicated three times.The composites of soil sample of the field were collected between 0-20 cm depth, analyzed for pre-cropping soil properties, and after treatments during harvest to determine the changes in soil chemical properties due to soil amendments.The results indicated significant difference (p < 0.05) among the treatments on all the parameters measured.The results showed that mineral content, dry matter, crude ash, starch, sugar, fats, crude protein and dietary fiber content were significantly improved in amended soil with ash materials when compared with sole NPK fertilization.The best performance on the growth and yield of sweet potato was significantly recorded from the plot amended with the integration of NPK plus rice husk dust of 18 t/ha while the control was the least.There were significant increases of soil organic carbon when treated with inorganic fertilizers and other ash material sources.The highest value of total nitrogen (0.17 g/kg) and lowest organic carbon (1.16 g/kg) was significantly recorded in the sole application of inorganic fertilizer whereas the highest increase in pH (5.7) and organic carbon (1.85 g/kg) were significantly recorded in the integration of NPK plus rice husk ash.It showed that sweet potato can perform optimally when there is integration of synthetic fertilizer amended with ash materials.