Corn (Zea Mays L.) Yield And Nitrogen Efficiencies as Affected By Different Nitrogen Rates and Redroot Pigweed (Amaranthus Retroflexus L.) Densities

Ali Vahedi¹*, Saeed Vazan¹, Hamid Rahimian Mashhadi², Majid Agha Ali Khani³ And Ali Kashani¹

¹Department of Agronomy, Faculty of Agriculture and Natural Resources, Islamic Azad University, Guilan Iran.

²Department of Agronomy, Faculty of Agriculture and Natural Resources, University of Tehran.

³Department of Agronomy, Faculty of Agriculture, Tarbiat Modarre University, Tehran Iran.

Corresponding  Author E-mail:Dr.alivahedi@yahoo.com

ABSTRACT: Field experiments were conducted at the Agricultural Faculty research field of the Islamic Azad University, Astara branch (Northwestern Iran) in 2007 and 2008. The main goal was to examine the effects of redroot pigweed density (Amaranthus retroflexus L.) on redroot pigweed leaf area index at 50% Corn (Zea mays L.) tassel time and corn grain yield, nitrogen recovery efficiency, nitrogen use efficiency and nitrogen utilization efficiency under different nitrogen rates. The experiments were established as split plots arranged in randomized complete block design with three replicates. The main plot was nitrogen rate at four rates 0, 100, 160 and 220 kg N ha-1. The sub plot was redroot pigweed densities, which were considered at four levels 0, 5, 10 and 20 weeds m-2 in an extended form to the corn farm. The results indicated that nitrogen application up to 160 kg N ha-1 with 5 and 10 weeds m-2 did not have any significant effect on leaf area index of redroot pigweed. However, this characteristic increased with the weed density at upper 160 kg N ha-1. Leaf area index of the weed was increased when 220 kg N ha-1 was applied, and its amounts in more densities was greater as well. The highest level of redroot pigweed leaf area index, in 20 weeds m-2 and application of 220 kg N ha-1 was calculated to be 1.82. Corn grain yield, nitrogen recovery efficiency, nitrogen use efficiency were 13.0 t ha-1, 46.2% and 60.5 kg grain/kg N applied, under 160 kg N ha-1 in weed-free corn condition. Eventually, it was found that the presence of 5 weeds m-2 up to 160 kg N ha-1 did not have any significant effect on corn characteristics; however, they were decreased by increasing weed density. The highest decrease was observed when was applied the highest amount of nitrogen under the highest weed density. Although, 20 weeds m-2 instead of 10 weeds m-2 caused more decrease in corn nitrogen use efficiency, the effect of these weed densities did not have any significant difference, statistically.

KEYWORDS: Corn; Competition; Yield, Nitrogen efficiency; Weed

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