Influence of vines production methods and their combination with time of harvest on tuber quality and yield of sweet potato

Availability of sufficient sweet potato vines is usually a problem during the planting season because most of the sweet potato vines from the previous harvest dry up before the next planting season. Also, in the process whereby the farmers are resulted to the prolonged multiplication of old vines for the planting of the new fields, the yield and quality of harvested tubers are reduced due to vines degeneration, diseases and pests infestation. Therefore, trials were conducted at Ajase-Ipo community of Irepodun local government area in Kwara state and Ifon community of Ose local government area in Ondo state of Nigeria in 2008 and 2009 to investigate vines producing methods and and their combination with different time of harvest. Three vines production methods investigated are nurseries, vines from sprouts roots and vines from successive planting (Farmers’ practice) and the harvesting time of sweet potato are 120, 140, 160 and 180 days after planting (DAP). The results indicated that, the effects of the vines production methods on the weight of fresh marketable tubers, weight of fresh unmarketable tubers, weight of total fresh tubers, tuber dry matter content and harvest index were significant. At both locations, nursery method gave the significantly highest values (15.2 and 13.8 t/ha) for marketable tubers in 2008 and 2009 at Ajase Ipo and (17.4 and 15.2 t/ha) at Ifon compared to sprouted roots and successive planting methods (Farmers’ practice). The combination of the methods of vines production and time of harvest effects significantly affected the average weight of marketable tubers at Ajase Ipo and Ifon. Nursery method gave the significantly highest values [(13.5 and 15.8 t/ha), (11.8 and 12.9 t/ha), (9.4 and 9.8 t/ha) and (8.4 and 7.9 t/ha)] at Ajase Ipo and Ifon at 120, 140, 160, and 180 days after planting (DAP) respectively compared to sprouted roots and successive planting methods. The combination of the methods of vines production and the time of harvest effects significantly affected the average weight of weevil free marketable tubers and badly infected marketable tubers at Ajase Ipo and Ifon. Consistently, nursery method gave the significantly highest values [(13.5 and 15.8 t/ha), (12.9 and 14.8 t/ha), (10.3 and 13.1 t/ha) and (8.6 and 11.8 t/ha)] weevil free marketable tubers at Ajase Ipo and Ifon at 120, 140, 160, and 180 DAP respectively compared to sprouted roots and successive planting methods that were not significantly different from each other. But, the least values [(6.9 and 7.3 t/ha), (5.8 and 4.1 t/ha), (4.8 and 3.1 t/ha) and (1.6 and 2.3 t/ha)] at Ajase Ipo and Ifon at 120, 140, 160, and 180 DAP respectively were recorded for successive planting method.