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MODULE 2 - OVERVIEW AND CHARACTERISTICS OF BIOFERTILIZERS Classfication of Biofertilizer  Overview on characteristics of organisms used in biofertilizers 1) Rhizobium Rhizobium is a genus of Gram negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitro...

MODULE 2 - OVERVIEW AND CHARACTERISTICS OF BIOFERTILIZERS Classfication of Biofertilizer  Overview on characteristics of organisms used in biofertilizers 1) Rhizobium Rhizobium is a genus of Gram negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen fixing association with roots of legumes. Rhizobium fixes atmospheric nitrogen symbiotically with legumes. Legumes can obtain their nitrogen from the atmosphere via the activity of nitrogen fixing bacteria of the genus Rhizobium. Rhizobium colonizes the roots of specific legumes to form tumour like growth called root nodules. Nodules act as a factories of Ammonia production. Rhizobium is abundant in soil and all of them not able to nodulate all types of legumes. On the basis of ability of rhizobium to form effective nodules with specific legumes are called Cross Inoculation. There are seven cross inoculation groups. With the formation of bacteroids a red pigment haemoglobin accumulate between the bacteroids is called “Leghaemoglobin”. The amount of leghaemoglobin and bacteroid production had direct relations with amount of N2 fixed by legumes. The process of N2 fixation is wholly dependent on the activity of enzyme “Nitrogenase” which is present in bacteroids. 2) Azospirillum It is an associative microphillic nitrogen fixer commonly found in association with roots of cereals and grasses. High N2 fixation capacity, low energy requirement and abundant establishment in the roots of cereals and tolerance to the high soil temperature (30 to 40° C). Due to these characteristic of Azospirillum, they are more suitable under tropical conditions. Due to high ability of N2 fixing and beneficial response under saline condition maintained high nitrogenase activity. They have ability to fix atmospheric nitrogen and produce phytoharmones. Azospirillum application observed that there was increased in yield with wide variation i.e. 10 to 64%. Most common species is Azospirillum brasilence is used and when applied with Azotobacter chrococcum production synergistic effect on yield of maize, sorghum and barley. 3) Azotobacter Azotobacter not only provides the nitrogen but produce variety of growth promoting substances like gibberllins, vitamin B and antifungal substances. Azotobacter has also ability to produce compounds against fungal pathogen like Fusarium and Alternaria. Due to these characteristics of Azotobacter there was increased germination and vigour of young plants. Another important characteristics of Azotobacter associated with crop improvement is excretion of Ammonia in the rhizosphere in the presence of root exudates and helps in nutrient uptake by plant The results from larger number of experiments conducted in last four decades have shown positive response to Azotobacter application on a crop like cereals, millets , vegetables, cotton and sugarcane and increased the crop yield by 10 to 30% Azotobacter 4) Blue Green Algae (BGA) It is also called Cyanobacteria. BGA are photosynthetic nitrogen fixing organisms passes nitrogen fixing species cells called “Heterocysts”. This algae is suitable to rice ecosystem and its abundance in rice field and is often referred as paddy organisms. It uses sunlight as a energy source and water as a source reducing agent for photosynthesis and nitrogen fixation. Most of the N2 fixing BGA of rice fields are filamentous consisting of vegetative celles including specialized called heterocysts. Heterocysts act as a micronodule for synthesis and N2 fixation BGA also synthesize and liberate growth promoting substances such as auxin and amino acids. They supply additional humus to soil improve aeration to rice roots and reduce the toxicity of sulphides. Example : Nostoc 5) Anabaena - Azolla Azolla is a primitive free floating water fern. There are six azolla species and out of these six species, Azolla pinnata is most common fern in India. It is grown in a ditches and natural ponds along with other weeds. The Azolla usually forms green mat over the water which often becomes reddish due to accumulation of anthocyanin pigment. It has an algal symbiont Anabena azolla with a central cavity. Anabaena - BGA known for Nitrogen fixation is associated with aquatic weeds. Azolla growing in paddy fields upto 25 to 30 kg N/ha and recent studies indicate that incorporations of azolla also reduces the requirement potash fertilizer to the tune of 25 to 35 %. 6) P-Solublizers Next to Nitrogen, Phosphorus is very important nutrient for plants and microorganisms. These insoluble soil phosphates are solubilized by a group of microorganisms are called phosphate solubilizing microorganisms. These PSM producing organic and inorganic acids and phytase enzymes and solubilize insoluble phosphate to soluble forms and make them available to crops. The PSM are bacteria, fungi and actinomycetes and they are as under : Bacillus megatherium, Aspergillus acva, Bacillus substilis , Penicillium digitatum , Pseudomonas striata , Trichoderma spp. Pseudomonas rathonis. It can also be used to enrich the compost. 7) VAM fungi These organisms are commonly found in association with agricultural crops, shrubs, tropical trees. VAM is differ from PSM. VAM do not solubilize the insoluble phosphorus but assimilate phosphorus, zinc and other nutrients for their own need i.e. for growth and reproduction and in addition translocate them in different forms to the roots of host crops. There are 120 species of VAM and they are associated with wheat, maize, soyabean, potato, grapes, banana, tea, sugarcane, coffee, etc. crops. These fungi formed by non-septate zygomycetous species belonging to genera Glomus gigaspora and Acuolospora entrophospora. VAM increases root absorbing surface like phosphorus, zinc, copper, potassium, aluminium, manganese and magnetite from the soil to the root cortex and increases the growth of associated plants by producing auxins and antibiotics, etc.