The crop is widely grown as an annual staple food and animal feed by resource-poor smallholders mostly on marginal infertile soils without purchased production inputs in countries of tropical and sub-tropical Africa, Asia and Latin America, with a total cultivated area >20 million hectares producing over 240 million tons of fresh storage roots, more than 70% of it being in Africa and Asia, with the greatest share in the former . Nigeria is the largest world producer of cassava . It is currently the world’s fourth most important staple and carbohydrate-enrichedfood after rice, wheat and maize and is an important component in the diet of over 800 million people across continents. In the tropical and sub-tropical countries, where cassava is produced, total human calories intake from cassava products exceeds 200 billion kcal/day . Because cassava roots are very low in protein content , human requirement for protein and other essential nutrients are commonly fulfilled by other food sources.
Cassava leaves are also consumed and constitute an excellent source for protein supplement , minerals and vitamins for the human diet in many African and Asian countries, as well as in certain regions of Brazil . Nevertheless, cassava roots and leaves are deficient in sulfur-containing amino acids . In countries where cassava is traditionally used directly for human consumption , particularly in Africa and Latin America, cultivars low in cyanogens are preferably used to avoid health hazards. When using cultivars high in cyanogens , much of the hydrocyanic acid is normally removed from cassava roots and leaves by using a mix of complex traditional methods and modern technologies during food processing and preparation . Its often poorly-processed food products contain some anti-nutrient elements such as free HCN, phytates and polyphenols, and particularly acetone cyanohydrin, which is commonly associated with an upper motor neuron disease known as “konzo syndrome” in some African countries . This occurs mainly with large intake of inadequately processed bitter-cassava products in areas hit by long drought and with shortages of balanced diets. Also, cassava leaves have value as a protein supplement in animal nutrition either in feed formulation for mono-gastric animals or as a fresh forage to supplement low-quality roughages in ruminant feeds .
All parts of cassava plants are valuable sources for animal feed that could be either fed or grazed fresh in case of sweet cultivars, or dried and ensilaged in bitter cultivars . For decades, Thailand was the largest exporter of cassava dried root chips, mainly to European countries, where it were used as a cheap component in the industry of animal feed concentrates. A significant portion of storage roots is used worldwide for starch extraction, glucose manufacturing, alcohol, and recently for biofuel. The cassava crop is propagated vegetative by using short woody stem cuttings planted horizontally, vertically, or inclined on flat or ridged lands at population densities from 5000 to 20,000 cuttings per hectare depending on the cropping systems and purpose of production . Lower population densities are practiced in intercropping systems, commonly with grain legumes and cereals such as maize and sorghum. When grown in mono-cropping systems, higher densities at 10,000 plants per hectare, or greater, are used. Sexual seeds are used mainly in breeding programs, though its use in commercial cassava production is a promising option to obviate constraints, particularly diseases, associated with vegetative propagation . Storage roots are generally harvested 7 – 24 months after planting, depending on cultivar, purpose of use and growing conditions. Due to root perishability and rapid deterioration after harvest , fresh roots have to be used immediately after harvesting, either eaten on the farm, marketed for consumption, processed for starch extraction, dried for flour production, roasted for food products and/or used for animal feed.
However, preharvest pruning in the three weeks before harvest decreases root deterioration because of increases in the total sugar/starch ratio in the roots . Cassava processing near production fields, makes it an ideal vehicle for rural development through creating employment opportunities in the areas where it is grown. Some of the processed food products are commonly known as farinha da mandioca in Brazil and bordering countries, gablek in Indonesia, and gari and foufou in West Africa . Also, in the Amazon region, local people prepare drinks such as Mingaoand Manicuera . Combining fresh cassava markets with those of its processed products should increase marketing flflexibility and crop profifitability, hence reducing the many risks often encountered by the producers.