OUT OF many micro organisms which are identified as bio fertilizers, Azospirillum, Phosphorus Solubilising Bacteria (PSB) and Vesicular Arbuscular Mycorrhizae (VAM) have a significant role in mulberry nutrition. Integrated use of these bio fertilizers will help in ensuring sustained productivity in mulberry.
Azospirillum stimulates mulberry growth and increases the number, length and weight of roots besides bud development. It invades the internal parts of the root. Where it promotes root hair development and branching. It fixes the atmospheric nitrogen in the roots of mulberry and produces plant growth hormones.
Application of Azospirillum at 20 kg/ ha/ yr with well-decomposed farmyard manure in five split doses reduces nitrogenous fertilizer application by 25 per cent.
Innoculation with Azospirillum also improves the economic characteristics of silkworm and silk.
It improves larval characteristics (like larval weight, pupal weight, cocoon weight, shell weight and shell percentage) and silk characterestics (like silk filament length and weight of silk).
Role of phosphorus
Phosphorus plays a major role in the balanced nutrition of plants to increase crop productivity. Only water soluble phosphorus is useful for the crop plants.
The availability of phosphorus can be increased by applying phosphorus solubilising bacteria (PSB).
It enhances the phosphorus use efficiency, produces the plant growth promoting substances, and also improves soil fertility and productivity.
The application of PSB at 10 kg/ ha/ yr with well-decomposed farmyard manure in five split doses reduces the quantity of phosphotic fertilizer by 25-30 per cent. Vesicular Arbuscular Mycorrhizae (VAM) is well known for their ability to absorb nutrients from the soil, particularly phosphorus. VAM plays a significant role in nutrient cycling in ecosystem.
The external mycelium extends several centimetres from the root surface and it then passes the depletion zone surrounding the root and exploits soil microhabitats beyond the nutrient depleted area where the small rootlets or root hairs cannot thrive.
Inoculation of VAM either individually or in combination with Azospirillum enhances the shoot and root length, number of leaves and the growth of plants.
There is an increase in plant height, shoot biomass and leaf weight of mulberry due to combined inoculation of Azospirillum and VAM.
The growth substances produced by Azospirillum are continuously released from root surface into the rhizosphere where the colony ofAzospirillum grows with photosynthate supplied by the host plant. Inoculation of Azospirillum influences VAM infection of mulberry roots.
Mycorrhizal colonisation increases the Azospirillum chroococcumpopulation in the rhizosphere and maintains it at a high level for a longer period of time.
The beneficial effect of free-living nitrogen fixing organisms on plant growth is mainly due to hormone production in addition to nitrogen fixation. PSB survives for a longer period in the rhizosphere of mycorrhizal roots.
The PSB renders more phosphorus soluble, while VAM enhances its uptake.
Department of Sericulture TNAU, Coimbatore