Today, the use of suitable cropping systems as an effective way to increase stability and improve the crop production have been considered by agricultural specialists. By creating diversity through intercropping, cropping systems will has found more dependence to internal and renewable resources and increases their stability. Such systems will provide an optimum conditions for the management of resources, while increase the diversity of production and reduce risks and losses. In order to study the effects of different levels of nitrogen and planting pattern on quality and quantity yield in mixed intercropping of berseem clover ( Trifolium alexandrinum L.) and barley ( Hordium vulgare L.) under conditions of weed interference, a field experiment was conducted in the research farm of Isfahan University of Technology, Iran, during March 2014 to July 2014 under irrigated system. The experiment was arranged in a split plot based on randomized complete block design with three replications. The main plots were involved different nitrogen rates in three levels (0, 30, 60 kg/ha) and sub plots were included different planting patterns of two crops in six levels (100% berseem clover + 100% barley, 100% berseem clover + 75% barley, 100% berseem clover + 50% barley, 100% berseem clover + 25% barley, pure stand of berseem clover and pure stand of barley), with additive series technique. Results showed that the highest yield of fresh forage, dry forage, crude protein and crude fiber were obtained by application of 60 kg/ha nitrogen in 100% berseem clover + 25% barley treatment while maximum percentage of crude protein was obtained at the same level of nitrogen but in pure stand of berseem clover treatment and the most percentage of crude fiber was achieved without nitrogen application in pure stand of barley treatment. The highest amount of light was received by canopy at level of the 60 kg/ha nitrogen in 100% berseem clover + 25% barley treatment. The maximum Land Equivalent Ratio (LER= 1.45) and Aggressivity Index (AI= 0.43) for dry forage were achieved at 100% berseem clover + 25% barley treatment. The maximum biomass of weeds were obtained when 60 kg/ha nitrogen applied in pure stand of bersem clover and the minimum biomass of weeds were achieved in mixed intercropping system of 100% berseem clover + 25% barley. In general, results showed that mixed intercropping of berseem clover and barley and application of 60 kg/ha nitrogen is much more efficient than pure stands, resulting in the highest yield. Also, combination of these crops could be reduce growth of weed. Keywords: forage crops, intercropping, land equivalent ratio, weed interference
