Effect of Weed Interference on Performance of Grain Corn (Zea mays L.) At Different Plant Densities

In order to evaluate the effect of weed interference and plant density on performance of grain corn, an experiment was carried out as split-plot based on randomized completed bloke design (RCBD) with three replications at the Agriculture Research Station, University of Tabriz, Iran in 2009. Plant density levels including: 5, 7, 10 and 16 plant/m -2 was allocated to the main plots and weed interference at three levels including: weed free, once in a row weed interference and perfect weed interference were assigned to subplots. The results showed that weed interference on grain yield, 1000 seed weight, kernel weight and number of ear had a significant effect. With increasing of natural weed interference during growth period, grain yield, 1000 seed weight, kernel weight and number of ear decreased. Also, interaction between weed interference and plant density was significant in kernel weight of ear. Between different densities the greatest grain yield with 1020 g/m -2 obtained from 16 plant/m -2 and weed free treatment. Weeds in treatments of once in a row weed interference 50 percent and treatments of perfect weed interference in long of growth period 75 percent grain yield decreased. Results showed that with increasing plant density, corn can increase its competitiveness with natural weeds of field increased the grain yield. Generally, the results indicate that the sensitivity to weeds interference especially in low plant density due to the effect of early competitive start may influence extremely the yield of maize.