Extinction Coefficient, Radiation Use Efficiency, Leaf Area and Dry Matter Distribution in Corn Canopy (Zea mays) under Competition with Pigweed (Amaranthus retroflexus L.)

In order to study the effect of completion with redroot pigweed on dry matter and leaf area distribution, leaf area, extinction coefficient and radiation use efficiency (RUE) in corn canopy (Zea mays L.) under competition with redroot pigweed (Amaranthus retroflexus L.) an experiment was conducted at Seed and Plant Improvement Institute (SPII), Karaj, Iran. Field study was carried out based on RCBD with 3 replication with redroot pigweed density (0, 3, 5, 8, and 10 plant per m of row) and time of emergence (same time with corn, 2-3 and 4-5 corn leaf stage). Results indicated that early emergence of redroot pigweed significantly distributed leaf area and dry matter to upwards of canopy layers and significantly increased yield loss (%) in compare to other treatment. Corn yield loss was 34% in early-emerged pigweed and decreased to 25 and 12 percent in 2nd and 3rd time of emergence respectively. Due to significantly decrease of corn LAI and increase redroot pigweed LAI in near the bottom of the corn canopy, the most value extinction coefficient observed in near the bottom. Result is also indicated that emergence of redroot pigweed in same time and 3rd time of emergence have minimum of extinction coefficient (K) (0.38) and maximum RUE (3.2 MJ), respectively. Generally, it is concluded that weed control until corn 4-5 leaf stage would be essential to reduce corn yield loss.