Modeling Light Interception and Distribution in Mixed Canopy of Redroot Pigweed (Amaranthus retroflexus) in Competition with Corn (Zea mays)

Abstract

To model light interception and distribution in the mixed canopy of redroot pigweed (Amaranthus rertoflexus) with corn, an experiment was carried out in randomized complete blocks design with factorial arrangement in Gonabad during 2006-2007 and 2007-2008 growing seasons. The factors used in this experiment was consisted of three corn densities (7.5, 8.5 and 9.5 plants per meter of row) and three densities of redroot pigweed (zero, 2, 4, 6 and 8 plants per meter of row). INTERCOM model was used through replacing parabolic function with triangular function of leaf area density. Vertical distribution of the species’ leaf area showed that corn had concentrated the most leaf area in layer of 50 to 150 cm, while redroot pigweed has concentrated in 40-60 cm of canopy height. Model sensitivity analysis showed that leaf area index, species’ height, height where maximum leaf area is seen (hm), and extinction coefficient had influenced on light interception rate of any species. In both species, the distribution density of leaf area at the canopy length fit a triangular function, and the height in which maximum leaf area was observed change by increasing the density. There was a correlation between percentage of the radiation absorbed by the weed and percentage of corn seed yield loss (r2 = 0.89). Ideal type of corn was determined until the stage of tasseling in competition with weed. This determination indicates that the corn needs more height and leaf area, as well as less extinction coefficient to successfully fight against the weed.