PRODUCTIVITY OF SWEET POTATO (IPOMOEA BATATAS (L.) LAM) AS AFFECTED BY NPK FERTILIZER RATE, INTRA-ROW SPACINGS AND VINE CUTTING LENGTHS IN THE NORTHERN GUINEA SAVANNA AGROECOLOGICAL ZONE OF NIGERIA

A two year field study was conducted during the rainy seasons of 2013 and 2014 at the research farm of institute for Agricultural Research, Ahmadu Bello University, Samaru Zaria North Western Nigeria (110 11!N: 70 381E and 686m above sea level) to determine the effects of NPK fertilizer rate, intra-row spacing and vine length on the productivity of sweet potato variety (Dan Zaria) in the northern Guinea Savanna Agro Ecological Zone of Nigeria. The treatment consisted of three NPK fertilizer rates (0, 150 and 300 NPK kg/ha), three intra-row spacings of (15, 30 and 45cm) and three vine cutting lengths (10, 20 and 30cm). The treatments were laid in split-plot design with NPK fertilizer rate and vine lengths in the main plot and intra-row spacing in the sub-plot and replicated three times. Results indicated that application of NPK fertilizer significantly enhanced most of the growth and yield components of the crop in the two years, namely: vine length, number of branches per plant, crop growth rate, relative growth rate, leaf area index and tuber yield (t/ha). Varying intra-row spacing from 15 to 45cm significantly increased most of the growth components due to decreased in competition among the plants.Planting of sweet potato using 30cm vine length performed better than 10cm or 20cm which were statistically similar in both years.Based on the results obtained in the study area it can be concluded that application of NPK fertilizer at 300 kg/ha, planting sweet potato on intrarow spacings of 45cm and 30cm vine cutting length could support good production of sweet potato in Samaru.