Rice is cultivated in tropical Asia (South and Southeast Asia) over an area of about 88.7 million ha, with an annual total production of nearly 183.8 million tons of rough rice, an average productivity of 2.7 t/ha (Table 1). Only 14% of the rice area in tropical Asia supports 2 crops of rice per year under irrigation. The remaining riceland is entirely rainfed, with varying water regimes. In ar…