Assessment of FAO Method for Estimating Canola Water Use in Hormozgan Province

Due to lack of accurately measured data on crop water consumption in Hormozgan province, the FAO- estimated crop water requirement data are used in most irrigation projects, without their prior assessment in terms of compliance and consistency with the region, which in turn, it may cause water loss or water stress to the plant. Thus, the present research was carried out to evaluate the FAO method precision in estimating canola water consumption in Hormozgan province. Accordingly, first, a lysimeter was installed in the center of a 4-ha ground area. Next, in and around the test site, the canola cultivar (Hyula-401) was cultivated and its water consumption was measured weekly by water balance equation. Climatic parameters such as air temperature, relative humidity, wind speed, sunshine, and rainfall were measured at the meteorological station located on the site and using them, reference crop evapotranspiration was calculated by FAO-56 Penman-Monteith Equation. Then, via multiplying it by the crop coefficient (Kc) identified according to the FAO guidelines, canola water consumption was calculated in weekly periods and compared with values obtained from lysimeter. Finally, the results showed that although the FAO method has a good accuracy in estimating the seasonal water use of the plant in the test area, if the purpose of the planning is irrigation at the farm level, this method could overestimate weekly water consumption from 0.06 to 1.5 mm day-1. Therefore, it is recommended to modify the estimated water consumption by the FAO method using the regression equation proposed in this research.