Influence of Weed Densities and Different Nitrogen Levels on Leaf Area Index (LAI) of Corn and Red Root Pigweed (Amaranthus retroflexus L.)


 Ali Vahedi1*, Zohre Bakhshai2, Rasoul  Fakhari3 1-Department
of Agronomy and Crop Breeding, Astara Branch, Islamic Azad University, Astara,
Iran 2-Department of Agronomy and Crop Breeding,
Rasht Branch, Islamic Azad University, Rasht, Iran  3-Weed Science M.Sc. Student,University of Mohaghegh Ardabili,
Ardabil, Iran   *Corresponding author
E-mail:       Received: 12 March 2013 Accepted: 12
November 2013     Abstract   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.