Determination of optimal planting date of rainfed wheat, in Kurdistan Province, Iran

The vast area of rainfed crops, compare to irrigated ones, depend mainly on climatic parameters such as rain and temperature. Wheat is the most important crop and the rainfed wheat area with 62.1 percent shares most of wheat cultivated area in Iran. Therefore, determination of paper planting date is very important. In this study, 40 years-daily rainfall and temperature data from 10 weather stations (which cover the whole studied area) were used to determine the proper planting date according to Eshtern definitions for effective rainfall and considered proper temperature of wheat germination, using kriging, cokriging and WMA (weighted moving average) methods. The prepared methods were evaluated at two probability levels (50 and 75 %) based on statistical criteria of MAE (Mean Absolute Error) and MBE (Mean Bias Error). The results of this study showed that there is not significant difference between the kriging and cokriging methods and they showed better results than the Inverse Distance Weighted. There, it is suggested that the ordinary-kriging and the first definition of Eshtern with 50% probability is used to determine the proper planting date of wheat.