Measurement of evapotranspiration and crop coefficient of pistachio trees in Rafsanjan region

Considering the significant increase of pistachio cultivation area in Iran and lack of water resources, accurate determination its water requirement is necessary. Since irrigation in the initial stages of pistachio is essential for adequate tree establishment, the main objective of this study was to measure the evapotranspiration of pistachio trees (ETc) between four to nine years of age, when the economical yields is achieved. This study was conducted in Rafsanjan Pistachio Research Institute station using a cubic concrete drainage lysimeter with  a 54 m2 surface area (6 m × 9 m) and a depth of 3.4 m. One-year old seedlings of Pistacia vera L. were cultivated inside and surrounding of the lysimeter. The amount of evapotranspiration and crop coefficient (Kc) was measured every 20-days during the eight-month growing season of pistachio using lysimeteric data. For the young trees For the young trees from four to nine years of age, the amount of seasonal evapotranspiration was 2291.2, 2507.8, 2739.4, 4516.0, 4604.0 and 5621.0 cubic meters per hectare with the mean Kc values of 0.108, 0.104, 0.15, 0.21, 0.28 and 0.33, respectively.The mean Kc coefficients of pistachio in five growth stages were determined as 0.2, 0.17, 0.22, 0.16 and 0.19, respectively.