Determination of evapotranspiration and crop coefficient of wheat, in Tabriz plain using lysimeter and comparing with FAO-56 approach

A lysimetric study was conducted to determine the evapotranspiration (ETc) and crop coefficient (Kc) of wheat (Triticum aestivum L., cultivar Alvand) during growing season in Tabriz plain, northwest of Iran. The obtained values were compared to estimations made by FAO-56 Penman-Monteith equation. Wheat evapotranspiration was measured in ten days interval using a drained lysimeter. Results indicated that seasonal ETc of wheat is 732 mm, from which an average of 132 mm was supplied by precipitation and the remaining (i.e. 600 mm) by irrigation. Highest and lowest amount of ETc was observed in 2nd decade of June and 2nd decade of December, respectively. The average amount of measured ETc was in good agreement (R2=0.92, NRMSE=0.11) with the estimated value by FAO-56 approach (721 mm). Similarly, the mean measured grass reference evapotranspiration value for the entire wheat growing season was 715 mm, which was statistically consistent with the estimated value (743 mm) obtained by FAO Penman-Monteith method (R2=0.98, NRMSE=0.08). Kc for the initial stage, mid- and late season were 0.54, 1.22 and 0.39, respectively. The Kc values were also in close agreement with those estimated using modified empirical equation of FAO56-PM. in climatic condition of study region.