Changes in phonological and physiological traits of corn under different nitrogen levels and pigweed density

To evaluate changes in phenology and physiological traits of corn under different nitrogen levels and pigweed density at flowering stage of corn, two experiments in split plot based on completely randomized blocks with three replications were conducted in 2010 and 2011 at the Islamic Azad University of Astara. Nitrogen in four levels of 0 (control), 100 (recommended nitrogen amount in the), 160 and 220 kg N.ha was the major factor; and the sub factor was density of redroot pigweed at four levels (0 (monoculture corn), 5, 10 and 20 plants per square meter) in accessional form at the farm of 704-single cross hybrid corn. The resulting data were analyzed using SAS software. The results showed that the interaction of Nitrogen × weed density was significant on traits of final plant height, dry matter production per unit area and leaf area index of corn at flowering stage. In addition the maximum height of corn was observed at consumption of 160 kg N.ha and by presence of 20 weed plants per square meter about 225.2 cm. Increasing pigweed density up to 10 plants per square meter increased plant height of corn at all levels of Nitrogen. Increase of nitrogen consumption produced more leaf surface of corn, and this increase was less in high levels of nitrogen. Corn dry weight per unit area decreases with increasing weed density, but in high levels of nitrogen, the effect of weed density was further.