Investigation the Effect of Transplanting Date on Intermittent Irrigation Planning in Paddy Fields Using SWAP Model (Case Study: Astaneh-Kochesfahan Plain)

Due to the lack of water resources, increasing of the water productivity index in a strategic and high water consuming cultivation like as rice is getting more important. Planting date and irrigation program are important factors in increasing the productivity of rice. This study investigates the effect of transplanting date on irrigation programe and rice yield and provides an acceptable strategy for determining the appropriate planting date with respect to climatic conditions and field characteristics. Therefore, SWAP model was calibrated in the Astaneh-Koushfahan plain with data of three paddy fields (Hashemi variety) and validated with data of two other paddy fields. The R2 index greater than 0.98 and RMSE-N less than 10% indicated that the model had acceptable accuracy for rice growth simulation. After validation, the optimummanagement of intermittent irrigation was obtained in planting dates 1, 5, 10, 15, 20 and 25 May. The results showed that in 2011 1 May was the suitable planting date due to higher irrigation water productivity. At this date, 9% allowable moisture depletion and 7 days irrigation intervals were proposed. Also, in this plain, the maximum and minimum moisture allowable depletion was 15 and 2%, respectively in clay and sandy loamy clay soil texture.