Zoning of planting and harvesting dates and length of growth stages of rainfed wheat based on precipitation and temperature data in Golestan province

In order to zoning of planting and harvesting dates and the length of growth stages of rainfed wheat in Golestan province, daily data of maximum and minimum temperatures and precipitation of 30 meteorological stations were used during the statistical period of 1991-2015. Due to the dependence of rainfed cultivation on the meteorological parameters, zoning maps were produced based on the probability level of 75%. Planting date and length of growth stages were determined based on the occurrence of the first precipitation equal to or more than 25 mm during a 10- day period in December and concept of Growing Degree-Days (GDD), respectively. To verify and check the validity of the results, zoning maps were compared with the various research findings obtained from farm-scale studies in Golestan province. Results showed that the highest frequency (area) and weighted average of rainfed wheat planting date in different regions were between 7th to 16th and 12th of December and for harvesting date were between 11th to 21th and 16th of June, respectively. Time duration of planting to emergence was between 34 to 89 days with a weighted average of 47 days, emergence to flowering was between 106 to 147 days with a weighted average of 122 days, flowering to maturity was between 31 to 68 days with a weighted average of 37 days and planting to maturity (total growing season) was between 170 to 244 days with a weighted average of 187 days. Regarding the occurrence of more and earlier precipitation and early appearance of cold season in the southern half and highlands of province compared to the northern plain areas, earlier planting and later harvesting dates in the southern half seem reasonable. Verification of these results with the findings of farm scale research showed that the prepared zoning maps had a good accuracy.