Irrigation scheduling of corn by difference in canopy and air temperatures for Tabriz climate conditions (Khosro-Shahr station)

Soil moisture, climate and crop measurements were applied in irrigation scheduling in a farm. In order to determine irrigation time of corn (Single cross 704) by difference in canopy and air temperatures, an experiment was conducted at the Agriculture and Natural Resources Research Center of East Azarbaijan (Khosro-Shahr). The experiments were as randomly complete blocks with three replications and with treatments of full irrigation during corn growth period (T1), limited irrigation with full irrigation at dough stage (T2), limited irrigation with full irrigation at flowering stage (T3) and limited irrigation with full irrigation at flowering and dough stages (T4). The canopy temperature was measured by an infrared thermometer and wet and dry temperatures of air were measured by a wet-dry thermometer. The stress lines for corn under specified climate condition were determined by computation of air and canopy temperatures differential values (Tc-Ta). For irrigation treatments, the lower baselines during corn growth period were determined by vapor pressure deficit, air and canopy temperatures differential values (Tc-Ta). The (Tc-Ta) was obtained as 4.7 oC in the upper baseline. Series of diagrams were presented as engineering procedure for irrigation scheduling of corn, based on vapor pressure deficit, air and canopy temperatures differential values. Stomatal conductance was measured along a leaf with different distances, at different leaves of a plant and at irrigation treatments by a porometer. Results showed that the stomatal along a leaf and at leaves of a plant had a variable values. So that the stomatal conductance increased with increasing distance from petiole to leaf tip and with increasing leaves number for soil surface to canopy. The stomatal conductance changes along leaf and its variability in leaves numbers were modeled as logistic functions. The temperature variability along leaf was modeled as Sinusoidal function. The stomatal conductance from limited irrigation treatments were similar and averaged 0.24 cms-1.