关键词: 水分利用效率, 水分利用效率

Abstract: In order to master the change of frost-free periods that effect on the agricultural production in Linfen, improve the frost forecast and prediction abilities, try the best to reduce the harm that frost-free periods cause in crops. Meteorological observation data of the first and last frost dates and frost-free period days was been used since the stations of 17 counties (areas) in Linfen, and the author adopted these climate statistical methods which there were about trend analysis, 5 years moving average, analyzed the basic features and changing trends of the first and last frost dates, frost-free period days. The results showed that: (1) the first frost day of Linfen delayed trend year by year, the trend rate was 1.327d/10 a. The city’s average first frost day was on October 18th, first appeared in September 20th, late appeared in November 5th, there are 46 days between them, maximum differential Puxian County was 56 days. (2) The trend rate of the last frost date was -1.83 d/10 a, showed a tendency to advance year by year, the city’s average last frost day was on April 2th, first appeared in February 19th, late in May 2th, there were 73 days between them, compared with the first frost day interval number nearly twice as many days. (3) The trend rate of the frost-free period was 3.156 d/10 a in recent 58 years in Linfen, which appeared a trend of increasing year by year, the variation rate of frost-free period was stable basically. The longest frost-free period appeared in Yicheng County in 1961, it had lasted for three hundred and one days. The shortest frost-free period appeared in Xixian County in 1980, it had lasted for one hundred and twenty-seven days; there were 174 days about the range.