VERTICAL LEAF AREA AND DRY MATTER DISTRIBUTION IN POTATO CANOPY IN RESPONSE TO WEED COMPETITION

To study the competitive effects of redroot pigweed (Amaranthus retroflexus) and lambsquarter (Chenopodium album) on potato, an additive experiment was conducted in the spring of 2004 and 2005 in split-split plot based on randomized complete block design with 4 replications at the Seed Potato Production Station of RAN in Firouzkooh. Treatments were included 2 weed species in main plots (Amaranthus retroflexus and Chenopodium album), weed density in sub plots (2, 4 and 8 plants per meter of row) and relative time of weed emergence in sub-sub plots (8 and 4 days prior to potato and the same time with potato emergence in 2004 and the same time with potato, 2 and 4 weeks after potato in 2005). Results showed increasing weed density resulted in reduction in potato Leaf Area Index(LAI), but leaf area distribution in canopy layers was not affected and maximum Leaf Area Distribution(LAD) was recorded in second layer (20-40 cm) of canopy in all treatments. In 2004, redroot pigweed in 2, 4 and 8 plants per meter of row put 29, 42.1 and 44.6 percent of LAI above the potato canopy, respectively. These amounts for lambsquarter were 30.6, 38 and 43 percent. By this mechanism, redroot pigweed and lambsquarter intercepted 54.8 and 53.3 percent PAR above the potato canopy in 2005 and 39.6 and 34.9 percent in 2005, respectively. increasing density of lambsquarter and redroot pigweed and sooner emergence of weeds resulted in more potato yield reduction