Determination of Irrigation Time by Measuring Stomatal Conductance in Corn Leaves

Stomatal conductance is one of the important indices to assess water deficit stress in plants. To evaluate stomatal conductance in corn leaves for scheduling irrigation, an experiment was conducted at East Azarbaijan Research Center for Agriculture and Natural Resources. The experiments were as Randomly Complete Blocks with three replications and with treatments of a: full irrigation, b: deficit irrigation from stages of 6-7 leaves to the end of ripening with full irrigation at flowering stage, c: deficit irrigation from stages of 6-7 leaves to the end of ripening with full irrigation at dough stage. The stomatal dimensions were determined by copy method. Stomatal conductance was measured along a leaf with different distances, at different leaves of a plant and at before and after irrigation events by a porometer. Results showed that the stomatal along a leaf and at leaves of a plant had a variable value. So that the stomatal conductance increased with increasing distance from petiole to leaf tip and with an increasing leaves number for soil surface to the canopy. The stomatal conductance changes along the leaf and its variability in leaves numbers were modeled as Logistic functions. The temperature variability along leaf was modeled as Sinusoidal function. Results also showed that the stomatal conductance from irrigation treatments were different. The stomatal conductance from two days after irrigation were similar and averaged 0.31 ms-1. The suitable time for irrigation and its cutoff were at stomatal conductance of 0.21 and 0.33 ms-1.