Field Evaluation of Yield and Ground Coverage of Sweet Potato Drought Tolerant Clones and Ornamental Varieties in Coastal Kenya

Abstract

Sweet potato is grown on a small scale in coastal Kenya due to shortage of planting material and use of varieties that are not drought tolerant. Most farmers plant their sweet potato on flat ground to avoid the labor-intensive land preparation. Some sweet potato varieties have ornamental value but this potential is yet to be exploited in coastal Kenya. This research was conducted to a) evaluate selected drought tolerant sweet potato clones under different watering regimes, b) assess the performance of conventional and ornamental sweet potato genotypes under different planting beds, c) evaluate different sweet potato clones for the production of sweet potato planting material under different vine planting methods, and d) assess the performance of selected sweet potato clones at different locations in coastal Kenya. A Randomized Complete Block Design with factorial arrangement of treatments was used in the on-station experiments. On-farm trials were conducted using a Randomized Complete Block Design. Nine drought tolerant sweet potato clones (coded 6.1A, 4.10, 7.8, 15.10, 7.6AO, 10.10B, 4.2B, 7.6B and 4.2A) and a farmer preferred variety were evaluated under four different watering regimes. Three drought tolerant clones and three planting beds were evaluated for storage root yield. Three ornamental sweet potato varieties and three planting beds were evaluated for ground coverage. Three drought tolerant clones and five methods of planting sweet potato vines were evaluated in the sweet potato planting material multiplication experiment. In the on-farm trials three drought tolerant clones and a farmer-preferred variety were evaluated. Data collected included yield, characteristics and nutritional contents of storage roots, percent ground cover and vine yield. The data were subjected to the analysis of variance using the general linear model procedure of the statistical analysis system. Storage root yield was reduced by about 70 and 50%, respectively, when water application was stopped early in the season, at two or three months after planting. Clones 7.6B and 4.10 produced higher storage root yield (5.1-11.5 t ha-1) than the rest of the clones, irrespective of the watering regime. Planting clones 4.2B and 7.6B on raised beds and ridges led to higher storage root yield (11.1-12.5 t ha-1) compared to planting the two clones on flat beds (6.9-8.3 t ha-1). Ornamental sweet potato varieties Purple heart and Green fingers gave higher percent ground coverage (68-72%), than variety Margarita (38%). In the long rains season, vine planting methods without lining produced longer vines (56.4-91.1 m m-2) than those with lining (14.8-21.8m m-2). In the on-farm trials, clone 4.2B produced higher number of marketable storage roots per plant than the other two clones (7.6B and 4.2A) and the farmer preferred variety. Planting sweet potato after the peak of the long rains season led to higher storage root yield per plant than at the start of the long rains season and during the short rains season. Clones 4.2B, 7.6B and 4.2A are recommended for further agronomic trials in coastal Kenya. It is also recommended that the crop be planted early in the planting season. Clones 4.2B and 7.6B are recommended for planting on raised beds or ridges. Ornamental sweet potato varieties Purple heart and Green fingers are recommended for evaluation in different locations in the coastal Kenya. Planting methods without lining are recommended for multiplication of planting material during the long rains season. Clone 4.2B is recommended for planting after the peak of the long rains season.