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Storage life of eleven cultivars of white yam (Dioscorea rotundata) grown with or without NPK fertilizer and the relationship with residual soil NPK
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A major constraint facing yam producers in southeastern Nigeria is poor storage of the tubers. Farmers in the area also opine that yams grown with mineral fertilizers tend to have shorter shelf life than those grown without mineral fertilizers. This study was undertaken to evaluate the effect of the applied mineral fertilizer on cultivar weight loss and the relationship between the weight loss and residual soil NPK. The selected (wound-free and about similar size) tubers were stored in a shaded but well ventilated traditional barn. Weight loss from tubers of eleven cultivars (ten cultivars were developed at IITA and the 11th one was a local best, Cv. Nwopoko.) of white yam (Dioscorea rotundata) was monitored monthly for six months following harvest in November at Nsukka, southeastern Nigeria. The tubers were from plots that received 15:15:15 NPK fertilizer mixture and those that did not receive any fertilizer. The result showed that there was a significant difference (p<0.001) between the loss in weight in tubers from fertilized and unfertilized plots. The average monthly loss in weight was 44% higher in tubers grown with fertilizer than those grown without fertilizer. The highest and the least losses in weight were obtained from IITA cultivars TDr 93-46 and TDr 95-127 respectively, for tubers from fertilized and unfertilized plots, while loss by the local cultivar was the second highest in both cases. A correlation of the tuber weight loss with residual soil NPK was not significant, however, tuber yield from unfertilized plots significantly correlated with residual soil K. Similarly tuber yield from fertilized plots correlated with residual total N. Some of the cultivars whether grown with or without fertilizer stored better than others. Cultivar effect was significant on weight loss (p<0.001) and more pronounced than fertilizer effect by more than 200%.