| By paying attention to the increasingly development that we observe in accuracy and correctness of short term predictions and also by consideration to the development of tool and instruments and methods of safeguarding plants against frost we can revise about determining length of growing season period. So in this study it has taken an action to extract 3 indexes: the length of potential growing season period and the length of risk management. The length of growing season period consists of chronological space between the occurrence of the last frost in spring and the first frost in autumn that is zero centigrade degree according to the threshold. The length of potential growing season was identified as chronological space between the last prolonged 3 days period having zero or under zero centigrade degree in autumn and it's last prolonged 3 days period in winter or the beginning of spring. The risk management was identified according to the space between the first or last frost days with the first or last prolonged 3 days frost. In continuation, for determining these 3 indexes in Iran, the data of minimum daily temperature of 62 synoptic stations for a 15 years period (1991-2007) during the month October to May was received from meteorology station. The result has shown that the length of growing season period in Iran varies from 161 to 365 day. So that Saghez, Ardabil and Shahr kord stations each with 161,167 and 169 day has the shortest length of growing season in Iran and the stations of southern coast like Chabahar, Khask, Bandar Abbas port, Lengeh port and Booshehr is 365 day. But using the index of length of potential growing season period instead of index of length of development period shows that the length of development period will increase from 4 days in Dogonbadan station to 58 days in Gorgan station. The station of Saghez, Ardabil and Shahr kord that had shortest length of growing season period in Iran ,have again the shortest length of growing season in Iran by this new index .But with the difference that the length of growing season period is 198, 202 and 211 days in order ,it means that in proportion to the length of growing season period ,35,34,41 days was added to their development period. The length of risk management period after southern stations that don't have frost ,the stations such as Dogonbadan ,Dehloran and Bam with 4,8,9 days are 3 stations that have the shortest period of risk management .Tehran, Dushan, Rasht ,Gorgan with more than 40 days have devoted the longest period of risk management in Iran. |
