Effect of Water Stress at Early Stages of Growth on Grain Yield of Corn Hybrid Varieties.

In order to investigate of water stress effects on yield of grain corn varieties at early stages of vegetative growth, experiment were conducted in4 complete block design with 5 replications at Mashhad and Neishabour on 2000 and 2001. Irrigation on three experiments (spring planting date) after plant emergence, was done based on 50, 70 and 90 percent of allowed soil water depletion. In the fourth experiment (summer planting date), irrigation was done regularly based on plant necessity (about 50% percent of allowed soil water depletion). The hybrid corn varieties on four experiments were KSC70.4 KSC64.7 KSC604 and KSC 30.1 In this study, the movement of water on unsaturated soil, was simulated based on Richards equation by LEACHM model. Analysis of variances showed significant differences between traits of hybrid corn varieties at two locations and years. Furthermore, irrigation treatments had significant differences for related traits to grain yield at least for one year. Comparison of irrigation treatment means on Mashhad showed no significant differences between 50 and 70 percent of allowed soil water depletion, but irrigation after 90 percent of allowed soil water depletion lead to significant reduction of grain yield at two years. Also, The summer planting date was better than sever stress (90 percent of allowed soil water depletion) on Mashhad., late and mid mature corn varieties (KSC70.4 KSC647 and KSC604) showed no significant differences. These varieties had the highest grain yield at tow location and years, while the early mature corn variety (KSC30) had the lowest grain yield. Combined analysis of variance was impossible due to significant F at Bartlett's test. Results of simulation of water and soil relationship showed that although evaporation and plant transpiration relationship are related to climate parameters, the soil structure should be intentioned in water stress effects. Although many researchers believe that low efficiency of first irrigations, results of this study showed that due to not enough extension of roots at first irrigations, the main part of water that is storaged in lower layers of soil is used for plant development with proper irrigation management. Also the results showed that uniform selection of MAD is related to soil properties