Corn and Soybean Intercropping Canopy Structure as Affected by Competition from Redroot Pigweed (Amaranthus retrofelxus L) and Jimson Weed (Datura srtramonium L)

In order to determine the role of plant leaf area in radiation distribution within the canopy and a better understanding of how crops and weeds intercept light a study of the complexity of plants is necessary. The effect of intercropping on leaf area distribution and dry matter accumulation in corn, soybean and weeds canopy was studied in a field experiment at a research field of Tehran University (Karaj campus), during 2007 growing season. Treatments were arranged in a factorial experiment based on randomized complete blocks with three replications. The treatments were five different mixing ratios of corn (Zea mays L.) and soybean (Glycine max L.) including 100/0, 75/25, 50/50, 25/75 and 0/100 (corn/soybean). Crops were planted at four levels of weed infestations, including weed free, infested to redroot pigweed (Amaranthus retroflexus L., AMRET), infested to jimsonweed (Datura stramonium L., DASTR) and mixed stands of both weeds species (DASTR+AMRET). Results showed that in weed free corn pure stand, 30.36% of the maximum leaf area was distributed in 90-120 cm layer, but when corn was grown with jimsonweed or infested with both weed species (DASTR+AMRET), the maximum leaf area were established in the upper layer. Soybean weed free monoculture produced 34.66% of its total biomass in the layer of 30-60 cm, but contaminated soybean with DASTR+AMRET, allocated 32.97% of its biomass in the 60-90 cm layer. In this treatment DASTR had also its maximum biomass (49.54%) in the 120-150 cm layer. Soybean canopy in monoculture couldn’t compete with weeds and was suppressed, but intercropped soybean with the corn especially in 50%: 50% mixing ratio, suppressed the weeds successfully. Therefore we can concluded that complementarily effect of corn/soybean intercropping created better condition for optimum utilization of solar radiation to successfully suppress weeds and maintain crop production.