Effects of potassium (K) sources and rates on tuber yield and storage life of white yam (Dioscorea rotundata poir) grown in an ultisol of southeastern Nigeria

The effect of potassium (K) sources at two rates on tuber yield and storage life of white yam was investigated. The four sources of potassium were; defatted palm kernel cake (DPKC), poultry manure (PM), their combination (DPKC+PM) as organic K source and combined NPK fertilizer as inorganic K source while the two rates were 37.5 and 75.0kg K tha-1 (low and high rates) based on their K content and a control (no application). These treatments were laid out in a randomized complete block design (RCBD) with four replications and the test crop was a local land race (Nwopoko). Planting was in April (on-set of rain) while harvesting was done at seven months after planting (November) in both 2010 and 2011. Healthy tubers of varying grades were selected from each treatment for storage studies over a period of six months. While in storage, the tubers were examined periodically for weight loss, rot incidence, sprout development and dormancy period. Tuber yields and storage data were subjected to analysis of variance. Two years (2010/11) mean indicated that among K source, poultry manure at high rate showed significant difference to the control and had 41.67, 20.48, 24.50 and 28.84% increases over combined NPK fertilizer at similar rate on number large (>1kg), small (<1kg), total number and total tuber weight respectively. Utilization efficiency test further buttressed the superiority of K sources at both rates over the control. Tubers from defatted palm kernel cake plots enhanced the storage life of the white yam tuber by recording the least loss in weight, rot incidence and sprout weight of 27.00, 9.40 and 4.75% respectively, and the longest dormancy period of 95.5 days. From the result, it can be concluded that K sources at high rate proved more effective than low rate. Poultry manure had significant increase over the control and combined NPK fertilizer in the tuber yield attributes. Defatted palm kernel cake enhanced the storage life of the white yam tuber significantly (P=0.05).Keywords: Root and tuber, potassium, yam and utisol