M.O Adeniji, G.O Obigbesan, R. Asiedu and M. Bokanga
Studies were carried out at the IITA, Ibadan, Nigeria on the influence of chemical fertilizers on tuber yield, storage and food qualities of two Dioscorea species: D. alata and D. rotundata. The treatments were: Control (No fertilizer), N, NP, NPK, and NPK-Mg, based on the recommended rates for yam in Nigeria, namely: 70 kg N/ha (as Urea), 50 kg P205/ha (as single super phosphate) 20 kg K20/ha (as muriate of potash) and 2 kg MgO/ha (as Magnesium sulphate). The various nutrient elements portrayed their differential effects on the fresh tuber yields. Whereas yield rose by 35% with NPK application to D. alata, only 15% increase was obtained by NP application to D. rotundata. Both yam species responded to Phosphorus application with yield improvements of up to 3.9 tons/ha (D. alata) and 5.9 tons/ha in D. rotundata. Storage attributes in the D. rotundata cultivar such as weight loss, percentage of sprouted tubers from 8 to 24 weeks after harvest, were not affected. Application of N alone reduced the general acceptability in the two cultivars when tubers were pounded. Balanced fertilizer combination NPK-Mg resulted in the best product quality.