Effect Of Corn Density And Spatial Arrangement On Redroot Pigweed (Amaranthus Retroflexus L.) Growth Indices

In order to study the effect of corn density and spatial arrangement on growth and physiological indices of redroot pigweed (Amaranthus retroflexus L.) a field experiment was carried out at Esfahan agricultural research station 2003. Treatments were arranged in a factorial split experiment based on RCBD with three replications. Factorial arrangement of corn densities (74000 and 111000 plant ha-1) and planting patterns (single row, rectangular twin row and zigzag twin row) formed the main plots. Split-plots referred to pigweed densities (0, 4, 8 and 12 plant m-1). In addition three experimental plots pigweed pure stand (4, 8 and 12 plant m-1) established in each block. In order to determine pigweed leaf area and dry matter accumulation, destructive sampling of pigweed started at 29 days after corn emergence with 14 days interval. Results indicated that pigweed leaf area index (LAI), total dray matter accumulation (TDM) and weed growth rate (WGR) decreased in corn existence. More corn density, more decrease in weed growth, in such a manner dense corn population, lead to 26.2, 16 and 19.7 percent loss in pigweed LAI, TDM and WGR respectively. These indices influenced more by corn twin row patterns compare to single rows, also effects of zigzag twin row were higher than rectangular twin row, in such a manner in the highest pigweed density, zigzag twin row reduced pigweed LAI, TDM and WGR about 7.9, 4.1 and 6.1 percent more than rectangular twin row pattern. Finally results showed that corn planting pattern effect on pigweed growth indices were lower than corn density. So extending of twin row patterns with increase density of corn can develop its competition ability and suppress the pigweed growth without chemical herbicide application.