Introduction Crop density enhancement is a method to increase yield per unit area. The spatial distribution of plants is related to radiation absorption. Therefore, it could play an effective role in photosynthesis and yield, since Crop Growth Rate (CGR) is a function of used radiation energy in photosynthesis. Totally, increasing radiation absorption efficiency and yield need sufficient leaf area and suitable distribution of leaves in canopy. Ahmad et al., (2002) planted sesame with different inter row- spacing (30, 45 and 60 cm), they reported that the maximum plant height and economic yield were obtained from inter row- spacing of 45 cm. Rahnama and Bakhshandeh (2006) planted sesame with different inter row- spacing (37.5, 50 and 60 cm) and the results showed that the number of capsules per plant, seed weight as well as seed oil per plant, increased with increasing inter row- spacing. Karasan et al., (2007) reported that decreasing inter row- spacing resulted in seed yield enhancement and reduction in number of capsules per plant. Material and Methods An experiment using split-plot based on randomized complete blocks design was performed. The experiment was carried with three replications in two years (2012 and 2013) at the agricultural research station of Ferdowsi University of Mashhad. For this purpose, the main plot was the density per square meter with three levels (30, 40 and 50 plants per square meter) and the sub main plot was planting pattern (rectangle, square and rhombic). The size of each plot was 2×3 meters. The distance between plots and blocks were 0.5 and 1 meter, respectively. Intra row- spacing for rectangle planting pattern for densities of 30, 40 and 50 plants per square meter was 6, 5 and 4 cm, respectively. In square and rhombic planting patterns, 2 lines was planted in each row and inter row- spacing for densities of 30, 40 and 50 plants per square meter were 18, 16 and 14 cm. economic yield measured at the end of growth season. In order to study the arrangement and planting density over two years of experiment, combined analysis was performed with SAS ver 9.1 and diagrams were plotted by using EXCEL 2010. Comparison of data mean was performed with LSD test at the level of 5%. Results and Discussions Interaction between planting pattern and density had significant effect on total dry matter, yield, the number of seeds per capsule and the number of capsules per plant. Harvest index, 1000 seed weight and the number of branches per plant were affected by plant density. Maximum dry matter was obtained from rhombic planting pattern with density of 50 plants per square meter and it was 8 and 13% more than squares and rectangles planting pattern, respectively. The highest yield was achieved from density of 50 plants per square meter in rhombic planting pattern at a rate of 1100 g m-2 in the year 2012. Maximum number of capsules per plant and seed were achieved from density of 30 plants per square meter in rhombic planting pattern with amount of 47 and 19.2, respectively in the year 2012. Increasing plant density from 30 to 50 plants per square meter decreased 1000 seed weight about 13 percent. Increasing plant density from 30 to 50 plants per unit area leads to lower harvest index (from 31 to 28 percent). Conclusions In order to achieve the highest total dry matter and economic yield, diamond planting pattern and density of 50 plants per square meter were better than the other. With reducing the density per unit area, biomass per plant increases due to less competition for light, nutrients and water. The maximum number of seeds per capsule and number of capsules per plant were obtained from diamond planting pattern with a density of 30 plants per square meter so it seems that at low densities, growth and branching of the plant increases because of enough space but there is no efficient use of the environmental resources. It's concluded that 50 plants per square meter in the diamond pattern is a suitable combination of treatments
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