Effect of poultry manure and NPK on yield and storability of orange-and white-fleshed sweet potato [Ipomoea batatas (L.) Lam

Abstract

Sweet potato [Ipomoea batatas (L.) Lam] is amongst the most commonly grown root crops in Sub-Saharan Africa. Comparatively,orange-fleshed cultivars of sweet potato are richer in beta carotene, a precursor to dietary vitamin A than white-fleshed ones. In spite of their health benefits, yields have been low in Africa due to low soil fertility. Studies were therefore conducted to determine the effect of amending soils with poultry manure and NPKmineral fertiliser on the yield and storability of orange-fleshed (OFSP) and white-fleshed sweet potato (WFSP). The field experiment was 3x2 factorial laid out in a randomised complete block design. Factors were fertiliser at two levels (poultry manure at 8.6 t/ha and NPK at 200 kg/ha) and control (no soil amendment) and sweet potato cultivars at two levels (orange-flesh and white-flesh). The highest yield of 12.4 t/ha was obtained from white-fleshed sweet potato (WFSP) to which poultry manure was applied compared with 4 t/ha for OFSP. Poultry manure treated plots generally produced the highest average number of tubers per mound (9) and average unit storage tuber weight of 0.64 kg. In orange-fleshed sweet potato (OFSP) tubers from plants treated with poultry manure and NPK 30% showed signs of rot during storage whereas 80-100% of tubers in other treatments were recorded with rots within 18 weeks. Tubers from orange-fleshed sweet potato plants treated with NPK had significantly lower levels of weight loss (25%) compared to other treatments. From this study, it can be concluded that although WFSP recorded higher yield under the poultry manure, but storage losses of up to 80% could make WFSP less available during the lean season. The OFSP tubers on the other hand had better storage-life irrespective of whether treated with poultry manure or NPK. Therefore, the cultivation of OFSP with the application of poultry manure or NPK, but preferably the former could extend food availability well into the lean season.    Key words: Sweet potato, poultry manure, fertiliser, storability.