Water balances and evapotranspiration in water- and dry-seeded rice systems

Rice is a crop that is usually grown under flooded conditions and can require large amounts of water. The objective of this 3-year study was to quantify water use in water- (WS) and dry-seeded (DS) systems. In WS systems, the field is continuously flooded, while in DS systems the field is flush irrigated for the first month and then flooded. Research was conducted on commercial rice fields where the residual of the energy balance method using a sonic anemometer and the eddy covariance method were used to determine crop evapotranspiration (ETc) and crop coefficient (Kc) values. In addition, inlet irrigation water and tailwater drainage were determined. Across years, there was no difference in ETc (averaged 862 mm), seasonal Kc (averaged 1.07), irrigation water delivery (averaged 1839 mm) and calculated percolation and seepage losses (averaged 269 mm) between systems. An analysis of the first month of the season, when the water management between these two practices was different, indicated that Kc and water use were lower in DS systems relative to WS systems when there was only one irrigation flush during this period, while two or three irrigation flushes resulted in similar values between the two systems.