Rice as a cereal grain makes up the major portion of staple diet consumed globally. Since a large portion of maize crops are grown for purposes other than human consumption, rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by humans.
Genetic evidence has shown the origin of rice in the Pearl River Valley region of China, some 8,200-13,500 years ago. From East Asia, rice spread to Southeast and South Asia. Rice was introduced to Europe through Western Asia and to the Americans through Europeans when they colonized the American continent.
Rice cultivation is suitable in areas with humid climate and high rates of rainfall as it requires abundant amount of water. Rice cultivation is a labor-intensive job therefore it is often cultivated in areas with low labor cost. Traditionally rice was cultivated by flooding the fields while, or after setting the young seedlings. This method does require proper planning and servicing of water damming and channeling but it decreases the growth of weeds and pests which have no submerged growth state.