Lemon Balm (Melissa officinalis L.) Water Requirement, Crop Coefficients Determination and SIMDualKc Model Implementing

The crop water requirements and coefficients should be determined for proper irrigation management and scheduling. The present study was conducted to determine water requirements, and single and dual crop coefficients of Lemon balm in a semiarid climate using water balance lysimeters during years 2012 and 2013. For these purposes, twelve water balance drainable lysimeters were used and three lysimeters were applied for grass evapotranspiration while three others were used for bare soil evapotranspiration estimation. Also, in six lysimeters, Lemon balm was planted in two groups including group A in which plant grew continually until the end of flowering stage and the appropriate time was reached for extraction, and group B in which plant was harvested three times, after reaching a height of 12-15 cm. The two year average water requirements of Lemon balm in two lysimeters groups, viz. groups A and B, were determined to be 539 and 415 mm, respectively. Single and base crop coefficients for lysimeters in group A were determined to be 0.68, 0.93 and 1.19, 0.42, 0.92 and 1.16, respectively for the initial, development and middle stages of plant. For lysimeters in group B, the average single crop coefficients on first, second and third harvests were determined to be 0.77, 0.77 and 0.81, respectively. In the present study, SIMDualKc model was calibrated and validated by comparing measured and simulated Dual Kc and evapotranspiration (ETc) values. The results showed the model capability and accuracy with low RMSE and MBE and high R2 = 0.89 for proper irrigation planning and scheduling in semi-arid climates.