Abstract: Sterile-type cool injury has serious impact on the rice production in Heilongjiang Province. To understand the cold tolerance of major rice varieties in the province and to define the quantitative index of sterile-type cool injury can provide scientific guidance for the local rice safety production. In this paper, four major rice varieties Kendao 12, Longdao 3, Longdao 7, and Kongyu 131 in the province were treated with different low temperatures at booting stage, and the effects of these treatments on the percentages of unfilled grains were analyzed. The results showed that when the average temperature was 15℃, the low temperature duration at booting stage was the key factor for the sterile-type cool injury of rice. Under the same durations of low temperature, the constant temperature 15℃ at day and night affected the test rice varieties most seriously. Under different low temperatures, the threshold value of slight sterile-type cool injury to the test rice varieties was 1-4 days or 5-8 days, and that of severe sterile-type cool injury was 5-8 days or more than 8 days, being varied with different varieties. Among the test four varieties, Kendao 12 and Longdao 3 had the weakest cold tolerance, Longdao 7 was medium, and Kongyu 131 was relatively stronger.

Key words: Wasteland, Soil moisture, Fixed field monitoring, Spatial and temporal change