Abstract:
Due to high cost, non availability and technical reasons, agriculture with high rate of chemical fertilizer is not practised in Nigeria and other African countries. There is need to investigate into the use of organic wastes and combined application of organic wastes and inorganic fertilizers in crop production. Yam production has not received research attention in this regard. Therefore experiments were conducted between 2008 and 2012 on the response of white yam (Dioscorea rotundata poir) to applications of goat manure, poultry manure alone or combined with each other and NPK fertilizer. Effects of treatments on growth parameters, tuber yield, plant nutrients, soil physical and chemical properties were investigated in field experiments conducted at Akure, southwest Nigeria. Compared with the control and NPK (400 Kgha-1 15.15.15), goat manure (GM), poultry manure (PM) and their combined application with NPK improved significantly (P>.0.005) soil moisture content, reduced temperature and bulk density. The PM, GM alone or combined increased soil organic matter (SOM), pH, N, P, and K. The manure alone or combined with NPK at different rates increased plant N, P, K, Mg and Ca significantly. The NPK alone gave highest values of leaf nutrient. Vine length, number of leaves and branches, tuber length and girth increased with rate of GM between 0 to 12t/ha. The 2, 4, 8, and 12t/ha GM and 400kg NPK increased yield by 52, 77, 192, 242 and 229% respectively. The PM, GM, at 6tha-1 and their combination at reduced levels, significantly increased growth parameters and tuber yield. The NPK, 6tha-1 GM, 6tha-1 PM, 4tha-1 GM + 2tha-1 GM, 2tha-1 PM + 4tha-1 GM, and 4tha-1 PM + 4tha-1 GM increased tuber yield by 258, 164, 214, 188, 150 and 150% respectively. The experiment showed that the combined application of NPK fertilizer at reduced rate with 12tha-1 manure gave similar or higher yield as recommended fertilizer. In 2011 compared with the control, 2tha-1 PM + 2tha-1 GM +300 kgha-1 NPK, 4tha-1 PM + 4tha-1 GM + 200kgha-1 NPK, 6tha-1 PM + 6tha-1 GM
+ 100kg ha-1 NPK, and 400kgha-1 NPK increased yield by 114, 105, 165, 84, 73 and 167% respectively. In 2012, 12tha-1 manure, 12tha-1 manure + 100kgha-1 NPK, 4tha-1 manure + 300kgha-1 NPK, 8tha -1manure + 200kgha-1 NPKF, and 400kgha-1 NPK increased yield by 99, 292, 117, 185 and 254% respectively. Animal manure at 12tha-1 can be used to reduce NPK requirement to 25%. Compared with the GM, PM was more effective in increasing soil nutrients, pH and yam yield. Sole application of GM at 8tha-1, combined application of 12tha-1 animal manure (6tha-1 PM + 6tha-1 GM) and the combined application of 12tha-1 animal manure with reduced level of NPK (to 25%) were recommended for optimum yield of yam.
