Agronomic Performance of Sweet Potato (Ipomoea batatas (L.) Lam) Fertilized with Poultry Manure Enriched with Oil Palm Refuse Bunch Ash in a Low Fertile Soil

A field experiment was conducted to investigate the efficiency of poultry manure enriched with oil palm refuse bunch ash (OPRBA) on the growth and yield of sweet potato in a low fertile soil. The experiment was laid out in a randomized complete block design with three replications. The treatments involved five rates (0, 2, 4, 6 and 8 t ha) of oil palm refuse bunch ash (OPRBA) in the first year of the experiment. In the second year, the treatments were 0, 4, 6, 8 and 10 t ha of OPRBA. All plots were treated with a basal application of 15 t ha of poultry manure. Data were collected on vine length (cm), number of branches, number of nodes, number of leaves, leaf area index (LAI) and total dry weight (g m) at 8 weeks after planting. Data on yield components were collected on tuber length (cm), tuber girth (cm), number of tubers, tuber size (kg), tuber weight (kg) and tuber yield (t ha). The results showed that vine length, number of branches, number of nodes, number of leaves and leaf area index and total dry weight increased significantly (p < 0.05) while increasing the rate of OPRBA. The highest tuber yield (50.22 t ha) was recorded for plants treated with 6 t ha of OPRBA in 2016. In 2017, plants treated with 6, 8 and 10 t ha OPRBA had the highest tuber yield (29.10, 30.00 and 32.00 t ha, respectively). Tuber yield correlated significantly (p < 0.05) and positively with total dry weight (r = 0.748), LAI (r = 0.938), number of branches (r = 0.679), number of leaves (r = 0.879), number of nodes (r = 0.440), number of tubers (r = 0.561), tuber girth (r = 0.751), tuber length (r = 0.864), tuber size (r = 0.952) and vine length (r = 0.940). It is therefore suggested that poultry manure at the rate of 15 t ha should be enriched with OPRBA at the rate of 6 t ha for optimum production of sweet potato.