Effect of Water Salinity in Sprinkler Irrigation on the CWSI Index for Irrigation Scheduling of Summer Maize

Determination of the appropriate time to irrigation is an important decision that farm planners are faced to it. Using canopy temperature for plants irrigation scheduling is one of the methods that have been attention by many researchers. In this way, several indicators have been proposed among which can be noted Idso Crop Water Stress Index (CWSI) method. This research intends to investigate irrigation scheduling of summer maize using crop canopy temperature in Ahvaz climatic condition in farming years 2013-2014 under sprinkler irrigation (fixed irrigation system) with two levels of salinity irrigation water ( S1=2.5 dS/m ,S5=5 dS/m) in three replications. Accordingly, the amount of crop water stress index in September was estimated for two treatments S1 (minimum salinity) and S5 (maximum salinity), respectively, 0.14 and 0.29 and in October, 0.18 and 0.27, respectively. Upper baseline equations for the S1 treatment, in September and October was calculated (Tc – Ta)u.l= 5.75 ºC and (Tc – Ta)u.l= 4.70 ºC, respectively. For the S5 treatment the upper baselines equations in September and October were (Tc – Ta)u.l= 2.94 and (Tc – Ta)u.l= 2.85 ºC, respectively. Lower baseline equations were calculated in S1 and S5 treatments and showed that the water stress in S1 treatment was lower than to S5 treatment due to the lower baseline. By using of measured data, for scheduling irrigation of maize in October and September with sprinkler irrigation method, some equations were determined. By using of the equations and comparing difference between leaf and air temperature measured by leaf and air temperature calculated (calculated allowable amount) can be detect time of irrigation in both treatments.