Separation the Evaporation and Transpiration in Maize Cultivation and Investigation of Their Response to Different Irrigation Levels

The purpose of this research was to investigate the response of evapotranspiration components of maize to different levels of water stress. This research was done as a completely randomized design. Treatments were irrigation at four levels; 100(I0), 80(I1), 60(I2) and 40(I3) percent of the crop water requirement. Daily crop evapotranspiration was measured based on soil water balance in a mini-lysimeter. Mini-lysimeters with and without mulch covering on the soil surface were used to separate the amounts of evapotranspiration components. The amounts of evapotranspiration components (ET, T and E) during the growing period were measured to be 424.5, 267.3 and 157.2 mm (in I0), 405.8, 245.4 and 160.4 mm (in I1), 360.5, 194.4 and 166.1 mm (in I2) and 303.7, 125.5 and 178.2 mm (in I3) respectively. The results showed that from I0 to I3, the amounts of ET and T decreased to 28.4% and 53% respectively, and the E amount increased to 13.4%. Therefore, in water stress conditions, the T portion was decreased to 35% and the E portion increased to 35%. The most amount of T occurred in the developmental period and the most amount of E occurred in the initial and final growth stages. But the highest response of transpiration and evaporation to water stress occurred in the middle period, in which transpiration decreased to 69% and evaporation increased to 253%. The existence of sensitive stages in the middle period of growth caused water stress to be most effective. The results indicated a reduction in transpiration and an increasing in evaporation in deficit irrigation conditions. Therefore, covering the soil surface and applying the suitable level of water stress in irrigation management will be effective factors for increasing the water use efficiency.