The Study the Light Competition of Lambsquarter (Chenopodium album L.) and Redroot Pigweed (Amaranthus retroflexus L.) With Potato

To study the light competition between potato with lambsquarter and redroot pigweed, an additive experiment was conducted in the spring of 2004 in split-split plot based on a randomized complete block design with 4 replications in Firouzkooh. The treatments included 2 weed species in main plots (Amaranthus retroflexus and Chenopodium album), weed density in sub plots of 2, 4 and 8 per meter of row and the relative time of weed emergence in sub plots of 8 and 4 days prior to potato planting with potato emergence at the same time. The simulation of light competition was done by INTERCOM model in potato and weed canopy. The results showed the leaf area indices in redroot pigweed were 56.1, 64.1 and 69.9 after canopy closure in 2, 4 and 8 concentrations over potato canopy, respectively. These amounts for lambsquarter were 48.5, 59.7 and 65.4 percent, respectively. They were 50.5, 58.5 and 62.3 for lambsquarter with different density while they were 55.5, 58.9 and 62.3 for redroot pigweed. By increasing weed density and leaf area, light absorption decreased in potato. The same condition was seen in the time of emergence so that by quickening in weed emergence, the percentage of potato light absorption decreased. Also, the percentage of weed light absorption is over potato canopy. In weed growing period during 8 and 4 days before or simultaneous with potato, light absorption for lambsquarter is beyond potato canopy with 52.9, 53.2 and 50.9 and they are 63, 56.3 and 52.9 for pigweed. By increasing density and quickening in weed growth as well as decreasing in light absorption by potato canopy, potato function fell down significantly.