Abstract
In order to study the effect various nitrogen and intercropping ratios on grain yield and some morphological traits of corn (Zea mays L.) and sunflower (Helianthus annus L.), a field experiment was conducted at the research farm of Agricultural Faculty of Islamic Azad University of Shoushtar (Khouzestan), in 2006. The split-plot set of treatments was arranged within a randomized complete block with three replicates. Treatments were various nitrogen rates (50, 100 and 150 kg N ha-1) as main-plots and different ratios of intercropping corn and sunflower (pure stand of corn, intercrop 75% corn plus 25% sunflower, 50% corn plus 50% sunflower, 25% corn plus 75% sunflower and pure stand of sunflower) in sub-plots. The results showed that the lowest and the highest grain yield were specified for corn (980 and 1225 g m-2), and for sunflower (346 and 387 g m-2) at 50 and 150 kg N ha-1, respectively. While in intercropping the highest and the lowest grain yield of corn were obtained in pure stand (1265 g m-2), and in 25% corn plus 75% sunflower ratio (957 g m-2). This was also valid for sunflower and resulted in decrease of grain yield of sunflower in 75% corn:25% sunflower intercrop. The oil percent of sunflower increased with decreasing sunflower proportion in intercropping. In addition increasing nitrogen levels resulted to increased land equivalent ratio (LER). So the highest (1.7) and the lowest (1.4) LER based on grain yield was achieved in 25% corn:75% sunflower and 50% corn:50% sunflower intercrops, respectively where 150 kg N ha-1 was applied.