ALI VAHEDI - Department of Agronomy and Crop Breeding, Astara Branch, Islamic Azad University, Astara, Iran
ZOHRE BAKHSHAI - Department of Agronomy and Crop Breeding, Rasht Branch, Islamic Azad University, Rasht, Iran
RASOUL FAKHARI - Weed Science M.Sc. Student,University of Mohaghegh Ardabili, Ardabil, Iran

In order to study the effect of increasing density of red root pigweed on leaf area index (LAI) of corn, and also on pigweed in different levels of nitrogen application, two field experiments were conducted during 2010 and 2011 crop years in Research Field of Azad Islamic University of Astara (north west of Gilan, Iran). The experimental design in each year was split plot based on randomized complete block design with 3 replications. The main factor was nitrogen amount in four different levels including zero (control), 100 (recommended nitrogen amount in the region), 160 and 220 kg nitrogen per hectare. The secondary factor was intensity of red root pigweed in four levels including zero (corn pure culture), 5, 10 and 20 plants per square meter. Results demonstrated that 25-35 days after growth of two plants, leaf area index of corn crop was more than red root pigweed in all levels of nitrogen and all intensities of pigweed. After this period, leaf area index increased in pigweed more than corn. The highest leaf area index of corn was observed in nitrogen application level of 160 kg per hectare and increasing nitrogen level and pigweed intensity resulted its decrease and increase in the corn and pigweed, respectively. The most grain yield of corn was acquired using 160 and 220 kg nitrogen per hectare, respectively with zero weed intensity and their values were 15.9 and 12.3 tons per hectare, respectively that their values decreased severely by increasing weed intensity in the farm.

Grain yield, Nitrogen fertilizer, Weed