Some observations on rice straw with emphasis on updates of its management.
Rice is the world's second largest cereal crop after wheat, however, it produces large amounts of crop residues. Only about 20% of rice straw was used for purposes such as ethanol, paper, fertilizers and fodders and the remaining amount is either removed from the field, in situ burned, piled or spread in the field, incorporated in the soil, or used as mulch for the following crop. Burning causes air pollution called the Black Cloud and loss of nutrients depending on the method used to burn the straw. Rice straw is unique relative to other cereal straws in being high in silica and lignin with low digestibility and protein content. Rice straw in developing countries is used as a main feed for ruminants. Enhancement of the nutritive value of rice straw with physical, chemical or biological treatments has been the focus of recent research work. Physical treatments such as crushing are related to breaking the silicified encrusting layer of straws. Chemical treatment of straw with alkalis such as ammonia and sodium hydroxide, has been commonly used for improving both apparent digestibility, bacterial colonization on cellulose and voluntary intake of straws. Fiber explosion (FIBEX) and soaking straws in wood ash extract processes showed significant increase in vivo digestibility. Supplementation with oilseed meal/cakes or rapeseed meal (RSM) and mulberry leaves as protein supplements was found to improve animal performance. Certainly, treatments using fungi and their enzymes for improving the quality of rice straw are relatively scarce. These techniques should be further developed. It was concluded that although several treatments have been used to improve the degradability and voluntary intake of rice straw, such as physical or chemical treatments, the practical use of these treatments is still restricted in terms of safety concerns, costs and potentially negative environmental consequences. Moreover, the application of ligninolytic fungi or their enzymes combined with chemical pre-treatments to rice straw may be an alternative way to shorten the period of the incubation and or decrease the amount of chemicals, affecting some synergy.