Effect of weed competition on yield, yield components maize cultivar Early 704 (the second culture) in Lorestan Kuhdasht

In order to effect of weeds relative time of emergence on single cross 704 Corn (Zea mays) yield was studied in different density levels of the mentioned weed. The experimental design was split plot based on Randomized Completed Block Design (RCBD) with three replications in 2012 was carried out in Koohdasht, Lurestan. The emergence time was considered in 3 levels of E1, E2 and E3 (emergence of the weed 14 days earlier, 7 days earlier and simultaneously with corn, respectively) as main plots and density of weed in 6 levels of D1, D2, D3, D4 and D5 (0, 4, 8, 12, 16 and 20 plants per m2, respectively) as subplots. The height, laef area index (LAI) of corn decreased with earlier emergence time and increasing the density of the Weeds. Also, earlier emergence time of weeds at high densities lead to the reduction in yield component (ear length, diameter and weight, number of seed row in ear, number of seed in row and thousand seed weight). The results showed that a decreasing in grain and biological yield of Corn, as the emergence time of Corn delayed in comparison with the emergence time of weeds. The maximum reduction in grain and biological yield of Corn was observed in 14 days earlier emergence of weeds compared to Corn in high density of this weed (20 plants per m2) with 100 and 99 percent respectively, as Corn plants were put in canopies of weeds plants. Totally, based on the results of this research it can be stated that as the number of the earlier emergence days of weeds compared to the Corn increase, the competitive potential of the Corn reduces and an intense decrease is being observed in its yield. Though, the increase in density of the weed resulted in grain and biological yield reduction, there was no difference between the process of reduction in high densities of weed.