Abstract: There is a long overwintering process in winter wheat growth period in Northern China, when aboveground biomass of wheat usually wilts partially or completely, that was a lack of consideration in crop growth models such as WOFOST and CERES-Wheat. In order to explore a revision method of biomass simulation during overwintering process of winter wheat, an extensive field investigation was conducted in 15 counties in the main winter wheat producing provinces of China, such as Hebei, Henan, Shandong and Tianjin, to observe spatial variation of wheat withering degree during winter. Meanwhile field experiments by means of divided sowing date and controlling base fertilizer were carried out in Gucheng and Hengshui agrometeorological experimental stations located in Baoding city and Hengshui city of Hebei province respectively, the impact of seedling growth state before winter on the post winter growth rate was investigated. The results showed that the aboveground biomass wilt degrees of winter wheat in Northern China were closely related to the meteorological conditions during the overwintering period. The withering rate of aboveground biomass by turning green increased linearly with decline of extreme minimum temperature over the overwintering period. The extreme minimum temperature could explain 86% of causes of aboveground biomass withering in the experimental years and regions. Under partial or complete withering of wheat leaves during the overwintering period, the seedling growth level of winter wheat before winter significantly affected post winter growth rate. The average growth rate of wheat from turning green to heading followed a parabolic function with the change of aboveground biomass per unit area before winter. Therefore, the initial value of aboveground biomass at the beginning of turning green needed in the crop models can be estimated according to the meteorological conditions in the overwintering period. At the same time, it is necessary and feasible to use the seedling growth of winter wheat before winter to correct the simulation of post winter biomass.

Key words: Winter wheat, Overwintering, withering, Frost damage, Crop model