In nature, there are a number of useful soil micro organisms which can help plants to absorb nutrients. Their utility can be enhanced with human intervention by selecting efficient organisms, culturing them and adding them to soils directly or through seeds. The cultured micro organisms packed in some carrier material for easy application in the field are called bio-fertilisers. Thus, the critical input in Biofertilisers is the micro organisms.
Bio-fertilisers are living microorganisms of bacterial, fungal and algal origin. Their mode of action differs and can be applied alone or in combination.
Based on type of microorganism, the bio-fertilizer can also be classified as follows:
Bio-fertilizer are mostly cultured and multiplied it the laboratory. However, blue green algae and azolla can be mass-multiplied in the field.
Characteristics Features of common Biofertilizers
|Name||Crops suited||Benefits usually seen||Remarks|
|Rhizobium strains||Legumes like pulses, groundnut, soybean||10-35% yield increase, 50-200 kg N/ha.||Fodders give better results. Leaves residual N in the soil.|
|Azotobacter||Soil treatment for non- legume crops including dry land crops||10-15% yield increase- adds 20-25 kg N/ha||Also controls certain diseases.|
|Azospirillum||Non-legumes like maize, barley, oats, sorghum, millet, Sugarcane, rice etc||10-20% yield increase||Fodders give higher/enriches fodder response. Produces growth promoting substances. It can be applied to legumes as co-inoculant|
|Phosphate Solubilizers (there are 2 bacterial and 2 fungal species in this group)||Soil application for all crops||5-30% yield increase||Can be mixed with rock phosphate.|
|Blue-green algae and Azolla||Rice/wet lands||20 -30 kg N/ha, Azolla can give biomass up to 40-50 tonnes and fix 30-100 kg N/ha||Reduces soil alkalinity, can be used for fishes as feed. They have growth promoting hormonal effects.|
|Microhizae (VAM)||Many trees, some crops, and some ornamental plants||30-50% yield increase , enhances uptake of P. Zn, S and Water.||Usually inoculated to seedlings.|
Each packet (200g) of inoculant is mixed with 200 ml of rice gruel or jaggery solution. The seeds required for one hectre are mixed in the slurry so as to have uniform coating of the inoculants over the seeds and then shade dried for 30 minutes. The treated seeds should be used within 24 hous. One packet of inoculant is sufficient to treat to 10 kg seeds. Rhizobium, Azospirillum, Azotobacter and Phosphobacteria are applied as seed treatment.
Seedling root dip
This method is used for transplanted crops. Five packets (1.0 kg) of the inoculants are required for one ha and mixed with 40 litres of water. The root portion of the seedlings is dipped in the solutions for 5 to 10 minutes and then transplanted. Azospirillum is used for seedling root dip particularly for rice.
4 kg each of the recommended biofertilizers are mixed in 200 kg of compost and kept overnight. This mixture is incorporated in the soil at the time of sowing or planting.
Use of VAM Biofertilizer
Use of Blue Green Algae (BGA)
Use of Azolla