comparsion of the fao penman-monteith method and class a evaporation pan with lysimeter data in estimating evapotranspiration (cicer arietinum l.) in khorramabad

lorestan and khorramabad province has major share in chickpea production region are the one of the largest producer of chickpea (cicer arietinum l.) in iran, chickpea with more cultivation area compare to the other plants, to estimate the chickpea water requirement. the aim of this research was to determine the crop coefficients of chickpea in a research field in lorestan agriculture faculty in 2013 to find (cicer arietinum l.) water requirement and different crop coefficients. for that, 4 drainable lysimeter was selected in which diameter and height were 0.45 and 0.8 m, respectively. the crop density was 50 plant per m^2. the water requirement of chickpea was estimated equal to 438mm. the potential evapotranspiration also was estimated equal to 554.2mm. more ever, the best pan coefficient also was determined by comparing with lysimetric results. different parameters such as rese, mbe, mae and r^2 were used to determine chickpea evapotraspiration. finally, the results showed that the fao model with error rmse, 0.174 is an optimum model for this region and snyder method was modified in the second accurately. the fao penman monteith method for calculating reference evapotranspiration in the region of 4.8 percent less than the amount of the lysimeters.