Risk Assessment of Frost Damage in Wheat

The resistance of the winter wheat drops rapidly when the plants begin to joint in early spring, in which season air temperatures fluctuate frequently. Winter wheat plants are prone to spring frost injury once strong cold air invades. The variation in wheat jointing date and the occurrence of low temperatures for frost injury (LTFI) in Huang-Huai wheat production areas are analyzed. The jointing date is affected mainly by cultivars growth. The occurrence of LTFI is mainly determined by the local climate. The variation in probability of wheat developing into jointing stage with Gregorian day could be expressed well by normal distribution function, and the accumulative probability of the occurrence of LTFI by exponential function. Based on these analyses, the mathematical model for assessing the degree of frost injury risk (DFIR) is then established. DFIR is mainly determined by such parameters as the termination date for some frost temperature (μ), the earliest jointing date (K), the standard deviation of the jointing date (σ), and the rate of variation in the accumulative probability of frost temperature with Gregoran day proceeding (b) etc. Parameters in the assessment model differ among the counties located in Huang-Huai and around area, leading to the different DFIR. According to the DFIR function, the zone with high DFIR is from the upriver region of Hanshui River that lies to the south of the Qinling Mountain, via the western Huang-Huai plain, to the plain lying in the mid-lower region of Huaihe River. The DFIR tends to drop gradually northwards and southwards, more rapidly for the former than the latter. Some effective measures could be chosen according to the properties of the parameters in the given area. In the area with high b value and low σ value, postponing the jointing stage may reduce the DFIR effectively; while in the area with high σ value, avoiding wheat jointing particularly early, appropriate cultivars and sowing date seem to be a good strategy to reduce DFIR; for the area of high DFIR calculated from the function with combined parameters, growing the frost resistant varieties becomes the most effective measure to avoid frost injury.