effects of corn canopy on seedling emergence of seven weed species

in this research corn were planted in 3 densities (8, 12, 16 plant/m2) in two planting patterns (single and double-row) with seven summer weed species, including redroot pigweed, green foxtail, annual bluegrass, common lambsquarter, jimsonweed, black nightshade and johnsongrass were planted. temperature, quality and quantity of light reaching to soil surface were measured and the number of emerged seedlings for each weed species was countered in three sampling dates. temperature fluctuation wasn't affected by density and planting patterns and was reduced with canopy formation. in all weed species 3 seedling emergence patterns were observed. in small seed species, redroot pigweed had one germination flush, so it was not respond to crop canopy. the number of emerged weed seedlings of annual bluegrass, common lambsquarter and green foxtail were significantly higher in bareground than under corn canopy. in double-row planting pattern was higher compared to the single-row and had three germination flushes. the number of emerged seedlings in the species with relatively large seeds had no significant difference between bareground and under corn canopy in jimsonweed and black nightshade. but it increased in johnsongrass under corn canopy compare to the bare ground. in all three species it was higher in double-row compare to single-row pattern. jimsonweed had three germination flushes but blacknightshade and johnsongrass had 1 germination flush.