The purposes of this study were evaluate the effects of biofertilizers inoculation on growth indices, yield and radiation use efficiency (RUE) in black cumin under Mashhad climatic conditions. This field experiment was carried out based on a randomized complete block design with three replications. This experiment was performed at Agricultural Research Station, Ferdowsi University of Mashhad, Iran, during two growing seasons 2007–2008 and 2008–2009. Treatments were (A) Azotobacter paspali, (B) Azospirillum brasilense, (C) Rhizophagus irregularis, A+C, B+C, A+B, A+B+C and control. In all treatments, except control, 100 g of seeds were inoculated with15 mg of each biofertilizer. Results indicated that leaf area index (LAI) and accumulative dry matter (DM) showed an increasing trend up to 1863°C d and a short declining trend afterwards. The relation between accumulative DM and absorbed photosynthesis active radiation (PARa) was linear. Radiation use efficiency (RUE) fluctuated from 0.55 gMJ−1 (control) to 0.89 gMJ−1 (B+C). Inoculation with biofertilizers enhanced root development and hence availability of moisture and nutrients, particularly nitrogen and phosphorus. Since these ecological fertilizers produce many growth regulators for the plant which promote LAI and accumulative DM and therefore yield, PARa and RUE enhanced.

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