Abstract: Result of field study showed that grain milking process of winter wheat could be described by the difference between leaf temperature and air temperature. When atmospheric vadiation was high and water supply was sufficient for plant grouth, the difference between leaf temperature and air temperature was relatively high and LAI decreased smoothly and the environment could be fit grain milking. When the radiation was high but plant suffer from water stress, the temperature difference was less and LAI decreased markedly, and the environment was unsuitable to grain milking. when the radiation was low, air temperature and the temperature difference were low, the environment was also unsuitable to grain milking. The paper present a mathematical model which can be used to guide crop production.

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