BiofertilizersBiofertilizers are carrier based preparations containing active strains of specific microorganisms, which help in enhancing the soil fertility either by fixing atmospheric N2, solubilization/ mineralization of P & K or decomposing organic wastes or by augmenting plant growth through producing growth promoting substances with their biological activities. Biofertilizer Agents are classified as (microbes in biofertilizers)1. N-fixer

2. P-Solubilizer/Mobilizer

3. Compost Accelerator

Biological N-Fixation:What is Biological N2 fixation?

Reduction of Dinitrogen (N2) to NH3 through biological means is termed as Biological Nitrogen Fixation

Why reduction of N2 is necessary?

Though atmosphere contains 79% of N, eukaryotes cannot utilize the N directly, unless it is reduced to NH3. Dinitrogen having triple bond and cannot be broken by higher plants.

Functions of nitrogen in the plant1. Inside the plant, Nitrogen converts to amino acids, the building blocks for proteins. These amino acids are then used in forming protoplasm, which is used in cell division. These amino acids are also utilized in producing necessary enzymes and structural parts of the plant and can become part of the stored proteins in the grain.

2. Nitrogen serves as the source for the dark green color in the leaves of various crops. This is a result of a high concentration of chlorophyll. Nitrogen combined with high concentrations of chlorophyll utilizes the sunlight as an energy source to carryout essential plant functions including nutrient uptake.

3. Chlorophyll is associated with the production of simple sugars from carbon, hydrogen, and oxygen. These sugars along with their conversion products play a role in stimulating plant growth and development along with higher protein content in the grain.

4. Nitrogen deficiency shows up in the yellowing or chlorosis of the plant leaves. The yellowing will start in the oldest leaves, and then will proceed to develop on younger leaves if the deficiency continues.

5. Plants will typically be shorter or stunted and grow slower than plants with sufficient Nitrogen. Nitrogen stress also reduces the amount of protein in the seed and plant. Tillering can also be reduced in small grains.

6. A Nitrogen deficiency can also affect the standibility of crops as grain fill occurs. If a plant is deficient in Nitrogen, it will draw Nitrogen out of the leaves and stalk for grain fill. This will weaken the stalk or stem causing standability problems.

Broadly the biological nitrogen fixing bacteria are divided into two groups

Symbiotic

Non Symbiotic In all the BNF system it is the nitogenase enzyme play crucial role in reducing dinitrogen to ammonia

Symbiotic Nitrogen Fixation

What is Symbiosis?

An intimate association between two different organisms for which the coexistence is deemed to be mutually beneficialSymbiotic Nitrogen fixation may be of three different types

Legume Rhizobium Cyanobacteria with plant/fungi

Frankia with trees

Rhizobium is symbiotic bacterium, occurs in the roots of different legumes & pulses, produce nodules and fix atmospheric dinitrogen inside the nodules. This Rhizobium present inside the nodule can be isolated and multiplied in laboratory .After appropriate multiplication the Rhizobium is mixed with carrier material in aseptic condition and used as biofertilizers for different pulse crops.

Necessity of Rhizobium Biofertilizers

Though Rhizobium occurs naturally in soil, but in most of the cases, either their population is highly insufficient or ineffective for proper nodulation traits. The low pH in the North Eastern Region is not conducive for proper nodulation that limits the Rhizobium cells to survive in adequate numbers in free living state. Under such situations the legume crops need to be inoculated with specific strains of Rhizobium inoculants each and every time.

The advantages of Rhizobium inoculation.

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Increases crop yield by 10-30%

Reduce Chemical fertilizer by 50% Leave considerable residual N (3-8kg of per bigha) after the harvest of the legume crop.

Benefiting the succeeding crop

Benefit the companion crop if grown along with legume as inter crop2) Cyanaobacteria:Cyanaobacteria are ecologically important in N2 fixing organisms especially in rice cultivation. Anabaena azollae is a small filamentous phototrophic cyanobacteria, live in a symbiotic association on Azolla(a heterosporous pteridophyte). It increases the production in rice field through fixation of nitrogen. Non-Symbiotic Azospirillum and AzotobacterNon Symbiotic Nitrogen Fixation can be divided into another three groups based on the oxygen requirements

Aerobic free-living nitrogen fixation. example-Azotobacter Microaerophillic (required low oxygen) , for example Azospirillum

Anerobic free living , for example Clostridium Out of sixteen known elements, N play vital role in crop production. Due to intensive agriculture and injudicious use of N through Chemical fertilizers jeopardize the soil ecosystem. To sustain the fertility of soils, maintenance of appropriate N2 fixing microflora is very essential. In this context, Azospirillum & Azotobacter play significant role as renewable nutrient source especially nitrogen in sustainable agricultural production.

Azospirillum This genus includes spirally curved bacteria which not only lives in rhizosphere of grasses but can also enter root cortex. It is an associative micraerophilic (low oxygen requirement) Nitrogen fixer which not only colonizes root mass and fixes N2 in close association with plant in an environment of low O2 tension. These bacteria induce plant roots to secrete mucilage substances which creates low O2 environment and helps to fix atmospheric Nitrogen. It has a wide host range, high N2 fixation capacity, low energy requirement, tolerance to high soil temperature thereby makes these suitable for tropical conditionThe positive aspect of this inoculant is that they produce plant growth promoting substance in addition to fixing the Nitrogen.Azospirillum biofertilizers is made of live cells of bacteria requied oxygen and free-living habitat.

Azotobacter:

This is a group of bacteria which are free living nitrogen fixer. The mechanism by which plants inoculated with Azotobacter derive its benefits such as increased biomass ,Nitrogen uptake is attributed to increase in nitrogen input by Biological nitrogen fixation, development and branching of roots ,production of plant growth hormones, vitamins, enhancement in uptake of nitrate, ammonium orthophosphate, potassium and iron improved water status of the plant and antifungal compounds. Estimation of Nitrogen fixation by free-living bacteria is difficult.Azotobacter biofertilizers can be used in non-legume crops mostly grown under upland condition.

Benefits of Azospirillum and Azotobacter inoculants

Benefits the crops by 15-25 kg of N/ha/Season

Grain yield is increased by 10-20%

Vegetative growth and leaf yield increased by 10-30%

Secretes growth promoting and antibiotic like substances

Can supplement 50% of nitrogenous fertilizer requirement by the crop.Microbes in Phosphate absorptions:1. Phosphate Solubilizing Microorganisms (PSM)What are the Importance of P-Solubilizing Microorganisms Phosphorus (P) is one of the major essential macronutrients limiting plant growth owing to its low bioavailability in soils.

Fertilizer P tends to be fixed soon after application and becomes mostly unavailable, resulting in low recovery by crops and a considerable P Fixation in soils

Microorganisms able to solubilize and mineralize P pools in soils are considered to be vital.

Bacteria are the predominant microorganisms that solubilize mineral P in soils, as well as mineralize the Organic P.

Bacillus & Pseudomonas are two major genera of Phosphate Solubilizing Bacteria. 2. Phosphate absorbers through Mycorrhiza- Aspergillus and Penicillium forms mycorizal associations belongs to fungi.Mechanisms of Inorganic P-Solubilizition

The main mechanism of inorganic P solubilization is through a decrease in pH. Another mechanism is by secretion of Organic acids such as Oxalic/Propionic/ Fumeric /Gluconic/Acetic/Citric/-Ketogluconic acid.Organic acid due to its dissociation, the Organic Anions make strong complex with Ca/Al/Fe and release phosphate into solution. Organic Cation such as H+ make complex with phosphate and may release into solution3. Role of phosphate in plant growth Photosynthesis and storage of sunlight energy

Formulation of simple sugars

Use of sugars and starches for growth

Transfer of energy during plant chemical reactions

Maintenance and transfer of plants genetic code

Development of new plant cells

Germination, size, number and viability of seed

Phosphate is key for: Quick emergence, Early vigor, Root growth, Maturity, Quality YieldZinc solubilizers Microbes:The zinc can be solubilized by microorganisms viz., Bacillus subtilis, and Saccharomyces sp. These microorganisms can be used as bio-fertilizers for solubilization of fixed micronutrients like zinc. The results have shown that a Bacillus sp. (Zn solubilizing bacteria) can be used as bio-fertilizer for zinc in soil instead of costly zinc sulphate

Fungi and their potential as biofertilizer

Types of Mycorrhizas

mycorrhizas were divided into the following three groups :(i)Ectomycorrhiza.It is found among gymnosperms and angiosperms. In short roots of higher plants generally root hairs are absent. Therefore, the roots are infected by mycorrhizal fungi which, in turn, replace the root hairs (if present) and form a mantle. The hyphae grow intercellularly and develop Hartig net in cortex. Thus, a bridge is established between the soil and root through the mycelia. Hyphae from the fungi extend from the mantle into the soil, which increases the surface area for water and mineral absorption. (ii)Endomycorrhiza (arbuscular mycorrhizae).The morphology of endomycorrhizal roots, after infection and establishment, remain unchanged. Root hairs develop in a normal way. The fungi are present on root surface individually. They also penetrate the cortical cells and get established intracellulary by secreting extracellular enzymes. Endomycorrhizas are found in all groups of plant kingdom.Arbuscular mycorrhizas, or AM (formerly known as vesicular-arbuscular mycorrhizas, or VAM), are mycorrhizas whose hyphae enter into the plant cells, producing structures that are either balloon-like (vesicles) or dichotomously branching invaginations (arbuscules). The fungal hyphae invaginate the cell membrane. The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them.

(iii)Ectendomycorrhiza.In the roots of some of the gymnosperms and angiosperms, ectotrophic fungal infection occur. Hyphae are established intracellularly in cortical cells. Thus, symbiotic relation develops similar to ecto- and endo-mycorrhizas.Benefits from Mycorrhizas to Plants

(i)They increase the longevity of feeder roots, surface area of roots by forming mantle and spreading mycelia into soil and, in turn, the rate of absorption of major and minor nutrients from soil resulting in enhanced plant growth.

(ii)They play a key role for selective absorption of immobile (P, Zn and Cu) and mobile (S, Ca, K, Fe, Mn, Cl, Br, and N) elements to plants. These are available to plants in less amount (Tinker, 1984).

(iii)Some of the trees like pines cannot grow in new areas unless soil has mycorrhizal inocula because of limited or coarse root hairs.

(iv)VA mycorrhizal fungi enhance water uptake in plants,(v)VA mycorrhizal fungi reduce plant response to soil stress such as high salt levels, toxicity associated with heavy metals, mine spoils, drought and minor element (e.g. Mn) imbalance.

(vi)VA mycorrhizal fungi decrease transplant socks to seedlings. They produce organic 'glues' which bind soil particles into semistable in aggregates. Thus, they play a significant role in augmenting soil fertility and plant nutrition.

(vii)Some of them produce metabolites which change the ability of plants to induce roots from woody plant cuttings and increase root development during vegetative propagation.

(viii)They increase resistance in plants and with their presence reduce the effects of pathogens and pests on plant health.

COMPOSTINGComposting is a process of biological decomposition of organic waste that is carried out by a group of active micro-organisms (bacteria and fungi) which break down the cellulolytic material and hasten the process of composting under aerobic condition at an elevated temperature.

Factors influencing composting are Number and species of micro-organisms, Oxygen levels, Particle size, Nutrient levels, Temperature, pH etc.Advantages of composting:-Reduction of volume and weightSoil conditionerMeans of land reclamationQuality of soil making it more productiveCompost increases soil aerationIt makes heavier soils easier to tillReduces soil erosionBuffer effect as a protection against that of chemical fertilizerMethods of Application:- 1. Seed treatment- Rhizobium, Azotobacter and Azospirillum, PSM, VAM - vesicular-arbuscular mycorrhizas (Inoculation of seedlings on the seedbed)2. Soil Application-Cynobacteria, Rhizobium, Azotobacter and Azospirillum, PSM, VAM (Inoculation of potted soil)3. Seedling root dip- Azotobacter and Azospirillu, PSM4. Waste Decomposers a) 1.Compost pit decomposition b) 2.Field (in situ) decompositionBenefits from Biofertilizers

Following are benefits from the biofertilizers :

(i)It is a low cost and easy technique, and can be used by small and marginal farmers.

(ii)It is free from pollution hazards and increase soil fertility.

(iii)On application of algal biofertilizers increase in rice yields ranges between 10-45 per cent and about 40-50 Kg N is left over in the soil which in turn is used for the subsequent crops (Venkataraman, 1972). after 3-4 consequent years, the algal effects become consistent and there is no need of using this practice as the parental inoculum is sufficient for growth and multiplication.

(iv) Cyanobacteria secrete growth promoting substances like IAA, IBA, NAA, aminoacids, proteins, vitamins, etc. They add sufficient amount of organic matter in soil.

(v)Cyanobacteria can grow and multiply under wide pH range of 6.5-8.5. Therefore, they can be used as the possible tool to reclaim saline or alkaline soil because of their ameliorating effect on the physico-chemical properties of the soil.

(vi) Rhizobial biofertilizer can fix 50-150 kg N/ha/annum.

(vii)Azotobacter and Azospirillum, besides supplying N to soil, secrete antibiotics which act as pesticides

(viii)Azolla supplies N, increases organic matter and fertility in soil and shows tolerance against heavy metals.

(ix)The bioferilizers increase physico-chemical properties of soils such as soil structure, texture, water holding capacity, cation exchange capacity and pH by providing several nutrients and sufficient organic matter.

(x)The mycorrhizal biofertilizers make the host plants available with certain elements, increase longevity and surface area of roots, reduce plant response to soil stresses, and increase resistance in plants. In general, plant growth, survival and yield are increased.Disadavantages of biofertilizers:

1. Their effects are is slower than chemical fertilizer

2. Biofertilizers are sensitive to temperature and humidity changes, hence difficult to store

3. Theyve much lower nutrient density than chemical fertilizers. Farmer would need to use large quantity to get the same yield.4. Some of them need special type of machines for spraying in the farm.5. In rural and remote areas, often its hard to find a retailer selling biofertilzers.