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ABSTRACT
Tuber crops are the most important land-grown food crops after cereals and grain legumes. They are either the staple or subsidiary food for about one-fifth of the human population, mostly in the developing countries of the tropics. Tropical tuber crops like cassava (Manihot esculenta Crantz.), sweet potato (Ipomoea batatas (L.) Lam) and yams (Dioscorea spp.)deserve special recognition owing to their higher biological efficiency (250 kcal/ha/day), ability to sustain under marginal environmental conditions, less incidence of insect-pests and diseases, high starch content (15–35%) and their excellent physico-chemical and biochemical properties in the preparation of several value-added products. Though tuber crops especially cassava grow under marginally fertile soil conditions, our experience under a long-term fertilizer experiment revealed their very high and positive response to manures and fertilizers. This review encompasses the research work undertaken in the soil fertility and nutrient management of tropical tuber crops covering aspects on nutrient uptake/ utilization, fertilizercum-manurial recommendations, critical nutrient concentrations, nutritional disorders and their corrections. Arising from this review yam requires 300kg/ha of NPK 15:15:15, cassava requires 75kg/ha of NPK 15:15:15 and sweet potato requires 200kg/ha of NPK 15:15:15. Yields of 15.60t/ha for yam, 34.12t/ha for cassava and 8.6t/ha for potato were the results from the applications of NPK 15:15:15. The use of Organic fertilizers such as poultry manure and cow dung at the rate of 10t/ha or application of 2000kg/ha of organomineral fertilizers has also improved the yield of these crops significantly.
