Yield and Growth Indices of Corn/Soybean Intercrop under Simultaneous Competition of Redroot Pigweed and Jimsonweed

In order to investigate the effect of corn/soybean intercrop on their yield and growth indices under competition with redroot pigweed (Amaranthus retroflexus L.) and jimson weed (Datura stramonium L.), a field study was carried out in Karaj during 2007 growing season. Treatments were arranged in a factorial experiment based on randomized complete blocks with three replications. Experimental factors were five different mixing ratios of corn (Zea mays L.) and soybean (Glycine max L.) including: 100: 0 (corn/soybean), 75: 25, 50: 50, 25:75 and 0: 100 with four levels of weed infestations: weed free, infestation to redroot pigweed, infestation to jimsonweed and co-occurrence of both weeds. Weed density was 15 plants per meter of row. Results showed that corn leaf area index, dry matter accumulation and crop growth rate was maximum in 75:25 (corn: soybean) ratio. The highest land equivalent ratio (1.33) and the most amount of corn yield (10875 kg ha-1) was also observed in this ratio, but decreased as the proportion of corn was decreased in mixture. The maximum corn yield loss occurred from multiple weed competition treatments. LAI, CGR, dry matter accumulation and grain yield (5898.3 kg ha-1) were maximum for soybean pure stand but showed a decreasing trend with decreasing soybean ratio. Appearance of high LER in all intercropped plots even in weed infested treatments indicate to profitability of intercropping as a non-chemical strategy for weed management.