Response of Alfalfa (medicago Sativa L) Growth at Low Accessible Phosphorus Source to the Dual Inoculation with Mycorrhizal Fungi and Nitrogen Fixing Bacteria

The study evaluated the response of alfalfa (Medicago sativa L) to arbuscular mycorrhizal fungi (AM) species Glomus intraradices and Sinorhizobium meliloti, strain 1021 regarding the dry biomass accumulation, mycorrhizal fungi colonization, nodulation and nitrogen fixation activity. Alfalfa plants were grown in a glasshouse until the flowering stage (58 days), in 4 kg plastic pots using leached cinnamonic forest soil (Chromic luvisols – FAO) at P levels 42 mg P 2 O 5 kg-1 soil (applied as 133 mg kg soil-1 tunisian phosphorite). The obtained results demonstrated that the dual inoculation of alfalfa plants significantly increased the percent of root colonization and acid phosphatase activities in the root tissue and in the soil in comparison with a single inoculation with Glomus intraradices. Coinoculation also significantly increased the total phosphorus and nitrogen content in plant tissues. Under conditions of dual inoculation high nitrogenase activity was established, especially in the floral budding stage as compared to the single inoculation 320 Stancheva et al.