LAUSR

Abstract Micro-nutrients especially zinc can not only increase the yield of sweet potato but can also improve the quality of tubers. Hence, experiments were carried out in 2015 and 2016 cropping seasons to determine the impact of various levels of ZnSO4 fertilizer on soil chemical properties, foliage and storage root yields and proximate qualities of sweet potato (Ipomoea batatas L.). The experiments consisted of 5 levels (0, 5, 10, 15 and 20 kg ha-1) of ZnSO4 fertilizer. These were arranged in a randomized complete block design and replicated three times. ZnSO4 increased (with the exception of P) soil chemical properties compared with the control. N, K, Ca, Mg and Zn were increased up to the 20 kg ha-1 ZnSO4 level in both years. ZnSO4 reduced P concentrations in soil as the level increased. For sweet potato performance, 5 kg ha-1 ZnSO4 fertilizer had the highest values of foliage yield (vine length and vine weight) and storage root yield. Using the mean of the two years and compared with the control, ZnSO4 fertilizer at 5 kg ha-1 increased storage root yield of sweet potato by 17.4%. On fitting the mean storage root yield data of the two years with a cubic equation, the optimum rate of Zn for sweet potato was found to be 3.9 kg ha-1 to achieve the maximum sweet potato yield. In this study, relative to the control, ZnSO4 fertilizer increased moisture and decreased the fibre contents of sweet potato. There were no consistent patterns of variation between the 5, 10, 15 and 20 kg ha-1 ZnSO4 treatments for proximate qualities except that the highest values of fat, protein, carbohydrate and ash was at 5 kg ha-1 ZnSO4.