Abstract: Based on the idea that the crop growth rate will decrease when environmental temperature is below or high above its optimal value and that if the decreases are not distinct the temperature is considered suitable for the crop growth, a mathematic model is proposed to evaluate the range of suitable temperature:And a similar mathematic model is developped for evaluating the indices of high and low injured temperatures to the crop growth. By the computations with the models it is poited out that in the growth period of the long -grained nonglutinous (indica) hybridized rice (No. 6) the optimal temperatures vary in the course of low-high-low pattern, and the indices of the high and low injured temperatures tend to the similar variation pattern. The range of suitable temperatures takes the course of big-small-big. It is obvious that the crop growth is sensitive to environmental temperature during the period of 11th leaf to boot stage. It is recognized by further analysis that the above regulations are identical to the courses of the crop growth rate and leaf area index of the colony, by which it is demonstrated that the regulations reflect the biochemical procedure variations in the plant body and the course of the colony architecture during its all life.

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