Influence of Fertilizer on the Colour and Starch Properties of Yam (Dioscorea spp) Tuber

Yam is a tuber crop grown for food security, cultural value and income generation. Due to its high nutrient-demanding nature, soil fertility is required for its cultivation. fertilizer is a crucial agronomic factor in yam production, Still, yam farmers are skeptical about fertilizer usage because of their fear of it exerting poor qualities on yam tubers. Limited information on the effect of fertilizer on yam tuber quality is available. Four varieties each of Dioscorea rotundata (TDr9518544, Danacha, Hembakwase and Ojuiyawo) and Dioscorea alata (TDa291, TDa0200012, TDa0000194 and TDa9801176) were cultivated under non-fertilization, manure fertilizer (4.5t ha‑1 poultry manure) and NPK fertilizer (90, 50 and 75 Kg N, P, K ha-1). The field experiment was conducted in the International Institute of Tropical Agriculture, Ibadan, Nigeria, in the 2017 and 2018 cropping seasons. The harvested tubers were evaluated for colour indices (L, a*, b* and browning index) and starch properties (starch yield, amylose and amylopectin, starch granule size and shape). Data obtained was subjected to analysis of variance using Statistical Analysis System software (SAS) package and means were separated using Duncan multiple range test with a probability of p≤0.05. Fertilizer did not cause browning or any significant change in the colour indices of the tuber flesh. starch yield (18.83 to 28.3%), increase in amylose was observed in D. rotundata in the order; manureNPKcontrol with manure having 92.66% and NPK 40.2% increase. Fertilizer had no significant effect on the granule size and shapes of the starches. Hence, fertilizer, especially manure and NPK, should be used to cultivate yam on nutrient-depleted soil without detrimental tuber colour and starch.