Rice is probably the most diverse crop. It is grown as far north as Manchuria in China and as far south as Uruguay and New South Wales in Australia. Rice grows at more than 300 meters elevation in Nepal and Bhutan and 3 meters below sea level in Kerala in India. Rice growing environments are classified into four major categories e.g. irrigated, rainfed, upland and flood prone. This categorization is based on several criteria such as water regime during growing, drainage, soils and topography.