Identification of susceptible areas and determination of the suitable date of cultivation of wheat in rainfed regions of Khorasan Razavi province

Because of the strategic importance of wheat (Triticum aestivum L.) and lack of precipitation amounts in Khorasan Razavi province، identification of suitable areas and the right time for this crop by using weather and climate data will increase yield of it. In this research، data of daily minimum & maximum temperature، and rainfall of 9 synoptic stations of the province were investigated in a 20 year statistical period (1989-2008). Offering the suitable temperature for germination of autumn wheat in the Korasan razavi province، susceptible areas were detected and mapping only with an emphasis on precipitation elements and considering the threshold of 300 mm. Also، start، end and duration dates of rainfall were calculated likely 50 and 80 percent by using the climatic conditions of region and then، were drawn maps of the most suitable times of cultivation of rainfed wheat. The results showed that the city of Ghuchan and Nishaboor are the most susceptible areas of the province and other cities، except Gonabad and Sarakhs are semi- susceptible regions of rainfed wheat farming. Also the first definition based on the start date of rainfall on first of October is day that total precipitation comes 5 mm، set as the best definition of determination of start date of effective autumn rainfall. Thus، considering the probability of occurrence of 80 percent and accepting the risk of 20 percent، the most suitable date of rainfed wheat cultivation for cities of province include: Torbat-heydariyeh 19 Nov، Sabzevar 20 Oct، Sarakhs 19 Nov، Ghuchan 24 Oct، Kashmar 29 Nov، Golmakan 20 Nov، Gonabad 10 Dec، Mashhad 13 Nov and Neishaboor 13 Nov.