Application of the Stomatal Resistance, Canopy Temperature and Crop Water Stress Index in Determining of Maize Irrigation Time

In order to investigate the water uptake limit of maize at different growth stages and scheduling the irrigation time, research was conducted in Imam Khomeini International University as a factorial experiment in a randomized complete block design. In the control treatment, the water requirement of the plant was supplied. But stress treatments included applying water stress (up to the temporary wilting point), at growth stages of 6-leaf, 12-leaf, flowering and seeds doughing. In the period of water stress, stomatal resistance, canopy temperature and meteorological parameters were measured. Based on the response of crop parameters to water stress, the readily available water (RAW) and crop water stress index (CWSI) were determined. The amount of RAW and CWSI at the 6-leaf, 12-leaf, flowering and doughing stages, were calculated equal to 45, 66, 61 and 70 percent and 0.37, 0.54, 0.63, and 0.47, respectively. The results showed that crop sensitivity to water stress, was different at maize growth stages. The flowering stage of maize was the most sensitive stage to water stress. Therefore, based on crop response, the irrigation time was determined at the time of water stress. Also, by calculating the exact volume of water required and applying variable irrigation intervals during growth stages, the crop water requirement to be supplied and irrigation losses were prevented. Under these conditions, due to the different sensitivity of water absorption at growth stages, it was possible to increase the water productivity.