Application effects of biofertilizers on the growth indices of black cumin (Nigella sativa L.)

Application of biofertilizers, especially plant growth promoting rhizobacteria (PGPR) and mycorrhiza fungus is one of the most important strategies for plant nutrition compared to chemical fertilizers, especially in sustainable management of agroecosystems. In order to investigate the effect of Azotobacter and Azospirillum bacteria and Mycorrhiza fungus on the growth indices of black cumin (Nigella sativa L.), a field experiment was conducted at the Agricultural Research Station of Ferdowsi University of Mashhad during growing season of 2007. A randomized complete block design with three replications was used. Treatments included: (A) Azotobacter paspali, (B) Azospirillum brasilense, (C) the fungus of Glomus intraradaices, C+A, C+B, A+B, A+B+C, and control without using bio-fertilizers. The Azotobacter and Azospirillum inoculations were applied as liquid and the Mycorrhiza inoculation was applied in solid form on the treated seeds with Arabic resin immediately before planting. The Arabic resin was applied to increase the adherence of Mycorrhiza to seeds. In all treatments except control, the amounts of 15 mg of each bio-fertilizer were applied for 110 g of seeds. The results indicated that the inoculation of black cumin with biological fertilizers significantly increased plant height, leaf area index, dry matter accumulation and crop growth rate compared with control. The maximum plant height was observed in Azospirillum+Mycorrhiza at 89 days after emerging. The highest and lowest leaf area index was observed in B+C (0.37) and control (0.22) treatments, respectively. The fast period of vegetative growth and dry matter accumulation were observed at 40-89 days after emerging with a small decline afterwards until physiological maturity. The maximum and minimum amounts of dry matter accumulation were recorded in the B+C treatment with 66.0 gm-2, and control with 38.3 gm-2, respectively. Crop growth rate reached to its peak in 82 days after emergence followed by a decreasing trend afterwards, its highest and lowest were observed in the B+C treatment with 14.5 gm-2d-1 and control with 5.8 gm-2d-1, respectively. Also, net assimilation rate reached to its peak in 61 days after emerging followed by a decreasing trend afterwards until the end of growth and its maximum and minimum were recorded in B+C treatment (47.2 gm-2d-1) and control (39.7 gm-2d-1), respectively. Further, investigations on quantity and quality of medicinal plants including black cumin in association with biological fertilizers effects will provide additional information.