Effect of Organic and Inorganic Manures and Time of Application on Soil Properties and Yield of Sweetpotato in a Tropical Ultisol

The effect of different rates of a mixture of organic and inorganic manure and time of application on the root yield of sweet potato (Ipomoea batatas (L) Lam) in a tropical Ultisol of South Eastern Nigeria was investigated during 2004 and 2005 cropping seasons. The research was carried out at the Eastern farm of National Root Crops Research Institute Umudike (NRCRI). The institute is located within latitude 05, 291 N and Long 7° 33 E1 of the Equator at an elevation of 122m above sea level. The aim was to determine the optimum rate and time of application of the mixture of organic and inorganic manure and their effect on some of the soil properties and root yield of Sweetpotato. The rates were 600kg/ha inorganic fertilizer,(NPK) 3.2t/ha poultry manure ,(PM) 450kg /ha NPK +0.8t/ha PM, 300kg/ha PM NPK+1.6t/ha, 150kg/ha NPK+2.4t/ha PM and a control. Time intervals were; at planting,2 weeks after planting, 4 weeks after planting and 6 weeks after planting. Results showed that amongst the various rates and time intervals investigated, application of 300kg/ha NPK +1.6t/ha PM of the two manure sources gave the highest economic root yield. The time interval of between 2-4 weeks after planting also gave the highest economical root yield of the crop .At this period also the recommended range of the investigated soil properties favourable to the root yield of the crop were obtained. These were pH, organic matter, Nitrogen, Phosphorus, Potasium and Exchangeable acidity.