In order to determine the effect of different plant densities in bean cultivars, an experiment was conducted as factorial layout based on a randomized complete block design with three replications at Agricultural Research Station, Ferdowsi University of Mashhad, during growing season the 2014-2015. Factors included four bean cultivars (such as Akhtar, D-81083Line, Naz and Goli), and three plant densities (including 13.3, 20 and 40 plants.m-2). Study has addressed some indicators including leaf area index (LAI), amount of absorbed radiation, dry matter accumulation and radiation use efficiency (RUE) in bean cultivars at different plant densities. The trend of increasing dry matter accumulation in all cultivars entered to the linear growth phase on the 20th day after planting and reached to its maximum on the 70th day after planting. The highest dry matter was obtained in Goli (300.4 g.m-2) and Naz (285.1 g.m-2) cultivars which was 32 and 30% higher compared to Akhtar and 30 and 28% higher compared to D-81083Line cultivar, respectively. The highest radiation use efficiency (2.2 g.MJ-1) was obtained in treatment at density of 40 plants.m-2 and was in Goli (2.01 g.MJ-1) and Naz (1.98 g.MJ-1) cultivars. With increasing plant density, maximum leaf area index in bean cultivars increased gradually to its highest level (40 plants.m-2) and due to plants ghosting, continued to decrease. This result can be used for modeling of leaf area. With increasing plant density due to increasing of leaf area index, the amount of absorbed radiation increased and therefore the time to reach maximum dry matter accumulation decreased and dry matter accumulation increased.

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