Growth and Yield Response of Improved Sweet Potato (Ipomoea batatas (L.) Lam) Varieties to Different Rates of Potassium Fertilizer in

A two-year field study was conducted during the growing seasons of 2007 and 2008 in Calabar, south eastern Nigeria to evaluate the response of two improved sweet potato varieties (TIS 8164 and Ex-Igbariam) to five rates (0, 40, 80, 120 and 160 kg K/ha)of potassium fertilizer. Factorial combinations of the treatments were arranged into a randomized complete block design with three replications. Results showed that Ex-Igbariam was more responsive to K application than TIS8164 as indicated by the production of longer vines, higher number of leaves and branches/plant and heavier vine dry weight at all the applied K rates. Averaged across the two years, revealed that Ex-Igbariam out-yielded TIS8164 by 12.5, 12.7 and 13.3 % for number of tubers/plant, weight of tubers/plant and tuber yield/ha, respectively. Application of K at the highest rate (160 kg/ha) significantly (P<0.05) increased vine length, number of leaves and branches/plant, whereas dry weight of vine, diameter of tubers/plant and weight of tubers/plant were statistically similar at 120 and 160 kg K/ha rates. Number of tubers/plant and tuber yield/ha peaked at 120 kg K/ha and 160 kg K/ha, respectively. Aggregate tuber yield/ha obtained at 120 and 160 kg K/ha rates were more than 7 and 8 times, respectively higher than the control treatments. Potassium fertilizer application at 120 to 160 kg/ha appeared appropriate for optimum yield for Ex-Igbariam in the study area and is therefor