Determination of crop water stress index for irrigation timing and yield estimation of corn

Corn (Zea mays L.) grown under a Mediterranean semiarid climate requires supplemental irrigation to maximize the grain yield. Since the cost of irrigation application has been increasing, elimination of unnecessary irrigation applications would improve economics of corn production. There has been much interest in the crop water stress index (CWSI) as a potential tool for irrigation scheduling and yield estimation. An experiment was conducted to monitor and quantify water stress, and to develop parameters for irrigation scheduling and grain yield of summer-grown corn as a function of CWSI under Mediterranean semiarid cropping conditions. Three irrigation treatments were based on replenishing the 0.9-m deep root zone to field capacity when the soil water level dropped to 25, 50. and 75% of available water holding capacity (AWHC). A dryland treatment was also included. The lower (nonstressed) and upper (stressed) baselines were measured to calculate CWSI. An equation that can be used to calculate the yield potential of summer-grown corn under a Mediterranean climate was developed using the relationship between the corn grain yield and the seasonal mean CWSI. Permitting the seasonal average CWSI value to exceed more than 0.22 resulted in decreased corn grain yield. The CWSI behaved as expected, dropping to near zero following an irrigation and increasing gradually as corn plants depleted soil water reserves. We concluded that CWSI is a useful tool to monitor and quantify the water stress of corn under a Mediterranean climate.