Comparison of Water Use Efficiency of Paddy Rice (Oryza sativa L.) among Locations and Interannual Variation in Humid Areas: II. Comparison among three locations and two cultivars in Shimane Prefecture

Water Use Efficiency (WUE) is a very important concept to indicate the relationships between crop production and water use. However there are few reports of WUE of rice in humid regions. Our objectives were to compare the WUE among three different locations and cultivars of paddy rice (Oryza sativa L.). Field experiments were conducted at three locations, Matsue (in 1991, '92), Izumo ('91) each less than 20m above sea level, and Akana ('91) at 444m in eastern region of Shimane Prefecture using the two rice cultivars, Nipponbare and Koshihikari. WUE was calculated from estimated canopy transpiration (T)¹⁾ and crop top dry matter. The relationship between the top dry matter and accumulated T was well fitted by a linear regression for each location and cultivar. The WUE at Akana was slightly higher than those at the other locations. It was considered that the lower saturation deficit in the mountainous location caused the high WUE, because the differences among the WUE decreased by correction of the saturation deficit. The WUE values of two cultivars were 4.0g kg^-1 (cv. Nipponbare) and 4.6g kg^-1 (cv. Koshihikari), respectively. There were no between-year differences in WUE at Matsue. We concluded that WUE of rice is almost constant for a given cultivar under humid conditions with similar meteorological profiles, although correction for the saturation deficit is required when there is a large difference in humidity between cultivated regions and years.