Rice (Oryza sativa) is an annual tufted grass, 0.5 to 1.8 m high (up to 5 m in deep water species) (Merteens, 2006) with usually 4 to 5 tillers. Inflorescence is a panicle, 50 cm long, bearing 50 to 500 spikelets. Spikelets contain 3 flowers, 2 of which are sterile. Fruit is a whitish to brownish grey, ovoid or ellipsoid caryopsis.
About 100.000 rice cultivars have been developed. Cultivars from Indica group are tall, leafy, strongly tillering, sensitive to photoperiod, resistant to diseases and unfavourable growing conditions. Cultivars from Japonica group are small, less tillering, less leafy, early maturing, resistant to lodging.
Rice is often grown as first crop in rotation or intercropped with cassava, maize, sorghum or cowpea. It can also be grown as sole crop and 2 or 3 crops/year may be obtained in many parts of the tropics.
Rice is one of the two most important staple foods with wheat. Rice production results in numerous products and by-products. After the harvest, the whole seed (rough rice, paddy) is processed into brown rice (cargo rice) by removing the hulls (chaff). The brown rice undergoes a series of operations that remove the germ and the bran fractions until obtaining the final white rice (polished rice). Rice straw is used to feed animals. Chaff is used as fuel, bedding, absorbent or packing material. The bran contains 14-18% oil that can be extracted and used in cooking as an anti-corrosive agent. Full-fat bran, defatted bran are used as feedstuffs.