More than 90% of the world's rice is produced in Asia. It is grown under diverse cultural methods ranging from well-drained upland conditions to wetland conditions where the soil is continuously submerged. The major system of establishing rice in Asia is transplanting. One of the major reasons for transplanting is weed control. In this system, the rice plant has a competitive advantage over the weeds from the start, and sometimes it is able to maintain this advantage throughout crop growth.