Assessing Rainfed Wheat Cultivation Risk and Suitable Time for Supplemental Irrigation in Tabriz plain

Regions Annual precipitation is one of the important factors for successful rainfed agriculture. Generally, cold and moderate climate regions with annual precipitation of 300 mm or more are suitable for rainfed wheat cultivation. Wherever, this amount is averagely 248.5 mm in Tabriz region over the last 30 years. In this research the possibility of rainfed wheat cultivation in the Tabriz plain based on precipitation amount and air temperature factors was investigated. For this purpose a set of 30 years data (1985-2015) was applied. The studied period was devided into 6 sub-perids of 5 years and the probability of success in wheat cultivation was evaluated in the rainfed condition. Results clarified that the supplemental irrigation was inevitable in the studied area. In order to determine the suitable time for supplemental irrigation practice, the autumn and spring precipitation amounts were calculated and subsequently these values were compared with corresponding crop water requirements. Finally, with investigation of wheat sensitive stages to water stress and comparison with seasonal rains, the suitable time of supplemental irrigation was proposed for June during filling stage. Over the recent 29 years the precipitation amounts of June have been less than minimum crop water requirement. Furthermore, the accurate management of the planting time can improve autumn precipitation utilization, as the autumn precipitations have been satisfactory in 3.8 years of each 5 years sub-period, averagely. The Growing-Degree-Days (GDD) index was applied for calculating the date of different growing stages of wheat. Also regarding to the importance of temperature in rainfed wheat growing process, the different phenological stages of the wheat from temperature view were investigated and the results were compared with required values.