In order to examine the effects of biological fertilizers inoculation on radiation use efficiency (RUE) in black cumin, a field experiment was conducted based on a randomized complete block design with three replications at Agricultural Research Station, Ferdowsi University of Mashhad, Iran, during two growing seasons of 2007-2008 and 2008-2009. Treatments were: (A) Azotobacter paspali, (B) Azospirillum brasilense, (C) Glomus intraradaices, A+C, B+C, A+B, A+B+C, and control. In all treatments, except control, 15 mg of each biofertilizer were inoculated with 100 g of seeds. Results indicated that RUE fluctuated from 0.55 g.MJ-1 (control) to 0.89 g.MJ-1 (B+C). Since these fertilizers are the cause of production of many growth regulators for the plant which promote photosynthesis and accumulative DM and therefore PARa and RUE enhanced.

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