investigation of corn/cowpea intercropping effect on suppresing the weeds

in order to study the weeds frequency and dry matter in corn and cowpea sole cropping and intercropping systems, an experiment using replacement and additive techniques was conducted using different combination of intercropping in seven levels with ratio of 1:1 (50% corn + 50% cowpea), 1:2 (33% + 67%), 2:1 (67% + 33%), (100% + 20%), (100% + 10%), 100% corn and 100% cowpea, two levels optimal and high plant density. a factorial experiment was conducted in the form of randomized complete block design (rcbd) with three replications at the research farm of agriculture college of zanjan university on 2007.results showed that the maximum yield of corn (8844 kg/ha) was obtained from intercropping system with ratio of 20% cowpea additive and the maximum yield of cowpea (640.5 kg/ha ) from the mxing ratio of 1:2 (33% maize+67% cowpea).the plant density and cropping pattern has influenced the dry matter of weeds. additive intercropping systems and sole of corn was affected on weeds control and dry matter decrease those to cropping systems others. in intercropping pattern of replacement method (33%cowpea+67% corn), was obtained least of weed dry matter. plant density and cropping pattern levels has significant effect (?=0.01) on weeds dry matter. the study of relative frequency of weed species indicated that red root pigweed (amaranthus retroflexus) 38% with density was the dominant species and chenopodium album, amaranthus albus, ipomoea hederacea, acroptilon repens, sophora pachycarpa, echinochloa crus-galli, xanthium pensylvanicum, and salsola kali respectively were the next category. values of ler>1 (land equivalent ratio) more than one in intercropping systems of additive increase 100% corn+20% cowpea and replacement 33%cowpea+67% corn, the advantage to intercropping systems showed a sole cropping.