The Effects of Irrigation-Off at Different Growth Stages, Planting Patterns and Plant Population on Grain Yield and Dry Matter Remobilization of GrainCorn (Zea mays L.)

This research was conducted in 2007 and 2008 cropping seasons in the experimental field of Shahid Salemi, Ahvaz, south west of Iran. In each year, the study consisted of a split split-plot experiment, using Randomized Complete Block Design (RCBD) with three replications. Four irrigation levels including irrigationoff at the 8 leaf, the 12 leaf and the tasseling stages and optimum irrigation were considered as the main plots _ _ and the subplots consisted of two planting patterns, one-and two-rows planting pattern respectively and plant population as the 3 treatment with three levels of 75000, 85000 and 95000 plant ha were placed in the subth 1 subplots. According to the results of combined analysis, the effect ofirrigation on grain and biological yields was significant. Unlike planting patterns, plant population had significant effects on grain and biological yields. Increasing plant population improved grain and biological yields. The interaction effects of irrigation and plant population on grain and biological yields were significant, the highest grain and biological yields were obtained from optimum irrigation and the highest plant population treatment. The effects of irrigation on rate, contribution and efficiency of dry matter remobilization and current photosynthesis were significant. The highest dry matter remobilization rate (474.5 g. m ) and current photosynthesis rate (411.28 g. m ) were 2 2 obtained from optimum irrigation treatment, whereas, irrigation-off at the tasseling stage had the lowest current photosynthesis rate and the lowest dry matter remobilization rate was obtained from irrigation-off at the 12-leaf stage treatment. The rate, contribution and efficiency of current photosynthesis in one-row planting pattern was higher than two-rows planting, whereas, the highest rate, contribution and efficiency of dry matter remobilization belonged to two-rows planting pattern. In dense population situations, due to the reduction in light penetration, senescence and chlorosis of leaves accelerated; the rate, contribution and current photosynthesis reduced although they caused a significant increase in rate, contribution and efficiency of dry matter remobilization. The study of the tripartite effects showed that the highest current photosynthesis rate and remobilization were obtained from optimum irrigation and one-row planting pattern in plant population of 85000 plants ha and optimum irrigation and two-rows planting pattern in plant population of 95000 plants ha 1 1 treatments respectively. Considering the results of this study, it seems that high plant population up to 95000 plant ha can increase grain yield in all irrigation treatments. 1