22 Role of microbes in agriculture as Bio-fertilizers

Dr Anita Singh

Introduction

Microbes or microorganism are minute living microscopic organisms which are not visible by naked eye. The study of microorganisms is called microbiology and Antonie Van Leeuwebhoek (1632-1723) is considered as father of microbiology. Microorganisms are present almost everywhere on earth. Microorganisms includes bacteria and archaea, protists, fungi, green algae. Micro-organisms can be used as bio-fertilizers to increase the crop yield. Biofertilizers are beneficial micro-organisms may have symbiotic association or may be free living in soil. To fulfill the food requirement, chemical fertilizers are used in large quantities. To increase the yield per hectre fertilizers and pesticides are used and it can be said that fertilizer is a food, and pesticide is medicine for plants in convention agriculture (Muraleedharan, 2010). Chemical fertilizer uses in agriculture make our country self-dependent in food production but leads to environmental pollution and also cause negative effects on living beings. Before adding any chemical fertilizers, the requirement of that fertilizer to soil must be analyzed. Without analyzing soil requirement and addition of more chemical fertilizers to the soil, the excess fertilizer may reach to water bodies by surface run-off or may percolates to ground water. Excess of fertilizers in water bodies reached by surface run-off leads to eutrophication condition. The side effects of indiscriminate use of chemical fertilizers in agriculture can be summarized as disturbances in the soil reaction, development of nutrient imbalances in plants, increased susceptibility to pests and diseases, reduction in legume root nodulation and plant mycorrhizal associations, decrease in soil life and environmental hazards such as water pollution and soil humus reduction (Deepali and Gangwar, 2013). It was felt from a long time to develop some low cost, effective and eco-friendly fertilizers which work without affecting nature and natural systems. Instead of using chemical fertilizers, a number of micro-organisms (like bacteria, fungi, algae) which are considered as beneficial for agriculture can be used. These agriculture beneficial micro-organisms are called bio-fertilizers. Bio-fertilizers can be defined as “a substance which contains living micro-organisms which colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrient and/or growth stimulus to the target crop, when applied to seed, plant surfaces, or soil. Whether the existence of a microorganism increases the growth of plants by making nutrients more available or replacing soil nutrients or increasing plant access to nutrients, as long as the nutrient status of the plant has been enhanced by the microorganisms, the substance that was applied to the plant or soil containing the microorganism, can be characterized as a bio-fertilizer” (Muraleedharan, 2010). Biofertilizers are mainly categories in three forms as shown in fig. 1.

The bio-fertilizers were initially identified by a Dutch scientist in 1888 there after bio-fertilizer use started with the launch of Nitragin by Nobe and Hiltner with a laboratory culture of Rhizobia in 1895 (Ghosh, 2004). In India, first commerical production of biofrtilizer started in 1956 under the supervision of N.V. Joshi. The ministry of Agriculture under the 7th plan initiated the real effort in the production, promotion and popularization of biofertilizers by implementing a scheme named “ National Project on Development and Use of Biofertilizer (NPBD)”. A National Bio-fertilizer Development Centre was established at Ghaziabad for promoting the traning programme related to production and promostion of biofertilizers along with six Regional Biofertilizer Development Centres at Banglore, Nagpur, Jabalpur, Bhubaaneshwar, Hissar and Imphal. Along with Government centres for biofertilizer production, there are many private units for the production of biofertilizers also. Government organising conferences and seminars from time to time for the promotion and utilization of biofertilizers. Different trade names of commercial biofertilizers like Rhizoteeka, Nodin, Nodosit, Rhizonit, N-Germ etc.

2. N2 bio fertilizers

Biological nitrogen fixation was discovered by the German agronomist Hermann Hellriegel and Dutch microbiologist Martinus Beijerinck. This type of biofertilizers helps in maintaining the nitrogen level in the soil. Nitrogen is required by the plants for their growth but the amount varies depending upon the crops like some crops need more nitrogen, some needs less. Biofertilizers fix atmospheric nitrogen either in the free form in soil or with legumes plants and make it available to the plant for its growth and development. Different type of nitrogen biofertilizers are used for different crops like rhizobium for legume crops, Azotobacteria for non-legume crops, blue green algae for rice. Nitrogen fixing micro-organism can have symbiotic association with plants, can live freely surrounding the plant, or can be associated with the plants. Different types of nitrogen bio-fertilizers are shown in fig. 2.

2.1. Symbiotic N2 fixing bacteria

Symbiotic association means both the partners get benefited. In this association the plant provides sugars and variety of minerals to the bacteria and bacteria provide usable supply of nitrogen to the host plant. In this symbiotic association, nitrogen fixing bacteria invades the root hairs of host plant, where they multiply in number and stimulate formation of root nodules. In root nodules, these bacteria convert free nitrogen into ammonia, which is utilized by the host plant for its growth and development. They develop the ability to fix nitrogen inside the root nodules only as they are surrounded by membrane of the host which is lined by a pink-red pigment called leghaemoglobin. There are different types of symbiotic nitrogen fixing bacteria as follows:

Rhizobia

Rhizobia is a symbiotic nitrogen fixing bacteria belong to family Rhizobiaceae (Rhizobia) and includes different genera like Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium, Mesorhizobium, and Allorhizobium (Vance, 1998). Fig. 3 shows the root nodules of rhizobia on vigna unguiculata. The bacteria infect the legume root and form root nodules within which they reduce molecular nitrogen to ammonia which is reality utilized by the plant to produce valuable proteins, vitamins and other nitrogen containing compounds (Rupali and Gangwar, 2013). Table 1 shows different rhizobium species for different legume species. Nitrogen fixing ability of varies depending upon the species Rhizobia and crop like Rhizobium leguminosarum fix 62-132 N kg/ha , R. japonicum fix 57-105 N kg/ha, R. trifoli fix 130 N kg/ha.

Fig. 3 Rhizobium root nodules on vigna unguiculata.(Source: https://commons.wikimedia.org)

Frankia

Frankia is the genus of nitrogen fixing mycelial bacterium (actinomycetes) that is symbiotically associated with non-leguminious plants. Frankia is cabale of infecting and nodulating group of eight families of mainly woody plants, called as actinorhizal plants (Benson and Silvester, 1993). Leaves of a few plants (e.g., Ardisia) develop special internal cavities for providing space to symbiotic nitrogen fixing bacteria, Xanthomonas and Mycobacterium. And these leaves provides constant source of nitrogen fertilizer to the soil.

Azolla anabaena

Azolla fixes nitrogen in association with blue green algae Anabaenaazollae. Azolla is a free floating water fern found on water surface. Anabaenaazolle is present in the leaves of Azolla. It fixes atmospheric nitrogen in paddy fields and also used as feed substitute for livestock’s. Azolla increases 10-20% yield in paddy crop and also suppresses weed growth.

2.2. Free living nitrogen fixing

Azotobacter

This is free living nitrogen fixing aerobic bacteria used as biofertilizer for non-leguminous plants like rice, cotton, mustard, vegetables. It occurs in the roots of Paspalum notatum (tropical grasses) and other spp. and adds 15-93 Kg N/ha/annum on P. notatum roots (Dobereiner et al., 1973). It also promotes the growth substances like vitamins, IAA and gibberlic acids. Increases the crop yield by 10-15 % and also help in maintaining the soil fertility.

Cyanobacteria

These are a group of one celled to many celled aquatic organisms and also known as blue-green algae like Nostoc, Anabaena, Oscillatoria, Lyngbia. They are prokaryotic organisms and phototropic in nature. In paddy fields, they play an important role by fixing atmospheric nitrogen and increases crop yield by 10-15%.

2.3. Associative Symbiotic Azospirillum–

This bacteria like Azotobacter, fix nitrogen in the rhizosphere in non-leguminous plants like cereals, millets, cotton, sugarcane, wheat, sorghum etc. This bacteria fixes nitrogen upto 20-40 Kg/Ha and also helps in uptake of plant nutrients.

3 Phosphate biofertilizers

Biofertilizers either solubilize insoluble forms of phosphate or scavenge phosphate (Fig. 4) from soil layers.

3.1. P Solubilizing Biofertilizers

P solubilizing biofertilizers includes phosphate Solubilising Bacteria (like Pseudomonas fluorescens, Bacillus megatherium var. phosphaticum, Acrobacter acrogens, nitrobacter spp., Escherichia freundii, Serratia spp., Pseudomonas striata, Bacillus polymyxa) and phosphate solubilising fungi (Aspergillus niger, Aspergillus awamori, Penicillium digitatum, etc.). These fungi and bacteria have phosphate solubilizing capacity and increases the cop yield 10-20 % (Cooper, 1959). Phosphobacterin are the bacterial fertilizers, firstly prepared by the USSR scientist.

3.2. P Mobilizing Biofertilizers

P mobilizing biofertilizers includes arbuscular mycorrhiza (like Glomus sp., Gigaspora Sp., Acaulospora sp., etc.), ectomycorrhizal (Laccaria sp., Pisolithus sp., Boletus sp., etc.) and orchid mycorrhiza (Rhizoctonia solani). Arbuscular mycorrhiza (AM) are symbiotic association between the fungi and roots of some specific higher plants. This is a symbiotic association, so both the partners are benefitted. The fungi absorbs nutrients like manganese, phosphorus, iron, zinc, etc. from the soil and pass it to the plant. VAM fungi or endomycorrhiza occurs in the roots of crop plants. VAM fungal hyphae increases nutrient uptake, stimulate root and shoot length, uptake of water, and heavy metal tolerance to plants. Orchid mycorrhiza are symbiotic relationship between fungi and Orchidasease family plant roots.

4.Silicate solubilizing bacteria

Silicate solubilizing bacteria (SSB) can play an efficient role in soil by solubilizing insoluble forms of silicates. Silicates accelerate plant growth, and increases leaf area for photosynthesis and abiotic stresses. Bacillus sp. plays an important role in silicate solubilisation. The accumulated Si not only improves growth and yield of these plants but is also involved in induction of systemic resistance (ISR) against pests and diseases (Vijayapriya and Muthukkaruppan, 2010).

5.Plant Growth Promoting Rhizobacteria (PGPR)

The group of bacteria (like Bacillus spp. and Pseudomonas fluorescence. Serratia spp. and Ochrobactrum spp.) that colonize roots or rhizosphere soil and beneficial to crops are referred to as plant growth promoting rhizobacteria (PGPR). They are also called as microbial pesticides. The PGPR inoculants currently commercialized that seem to promote growth through at least one mechanism; suppression of plant disease (termed Bio-protectants), improved nutrient acquisition (termed Bio-fertilizers), or phyto-hormone production (termed Bio-stimulants). (Mohapatra et al., 2013).

6.Methods of application

There are four types of application method of bio-fertilizers- seed treatment, soil treatment, seedling treatment and set treatment. Table 2 shows different types of bio-fertilizers and there application method on different crops.

6.1 Seed treatment

This method is mainly used for cereals (wheat, sorghum, maize, etc.), oilseeds (groundnut, mustard, sunflower), pulses (cowpea, green gram, black gram, etc.). In this treatment, a suspension culture is prepared by mixing bio-fertilizer and water in ratio of 1:2 (like 200g bio-fertilizer in 400 ml water). Then the culture suspension was sprinkled over the seeds heap and mixed properly by hand to make a thin coating of bio-fertilizer on seeds. Then the seeds are spread in shade for some time for dying and then sowing. One packet (200g) is sufficient to treat 10-12 kg seed.

6.2 Soil treatment

In this method, mixture of bio-fertilizer and soil (or cattle manure) sprinkled with water is spread into the soil at sowing time. The amount of bio-fertilizer varies with duration of crop like for short duration crop like less than 6 months, 10-15 packets (200g each) mixed with 40-60 kg of organic mature or soil per acre of land. And for long duration crops, the amount increase from 20-30 packets of bio-fertilizer (200g each) mixed with 80-120 kg of organic manure or soil per acre of land.

6.3 Seedling treatment

This method is applied for crops like paddy, onion, chilly etc., where the seedlings are dipped in bio-fertilizer suspension. Bio-fertilizer is mixed water in the ratio of 1:10 (200g bio-fertilizer in 2 litres of water). The root tips of the plants are dipped in the suspension for 15-30 minutes and transplant immediately.

6.4 Set treatment

This method is applied for sets of sugarcane, pieces of potatoes and base of banana suckers. In this method the ratio of bio-fertilizer to water is 1:50 (1 kg of bio-fertilizer in 50 liters of water. The planting material pieces are immerged in bio-fertilizer suspension for 30 mins after that dried in shade for some time before planting. After plantation, the field is irrigated within 24 hours.

Table 2 Different types of bio-fertilizers and there application method on different crops

a)Benefits of bio-fertilizers

 Increase the crop yield by providing nutrients to plants. They are safe and eco-friendly.

Leaves no traces of toxins or harmful chemicals into soil and in plants. Increases the fertility of the soil.

They suppress diseases in plants as well as harmful microorganisms is soil. Increase the nutrient uptake by the plants. 

They also produce growth hormones.

They are safe to handle as compared to chemical fertilizers. Decreases the dependence on chemical fertilizers.

Increases the nutritional quality of final product.

b)Bio-fertilizer Production and Commercially available bio-fertilizers

There is a long list of companies dealing with bio-fertilizer production like National Fertlizer Limited Company, Niku Bio-Research Lab, Nitro Laboratories, Orgaman, Orrisa Agro Industries Corporation Ltd etc., are producing bio-fertilizers. Fig. shows the diagramatic representation for production of biofertilizers. Tamil Nadu Agricultural University produce different types of biofertilizers and cost of their biofertilizers are as Azospirillium Rs. 40/kg, Liquid biofertilizer Rs. 300/lit, Phosphobacteria Rs. 40/kg, Rhizobium Rs. 40/kg, Azotobacter Rs. 40/Kg, VAM Rs. 30/kg and Azolla Rs. 5/Kg (Source: http://agritech.tnau.ac.in)

Fig. 5 showing procedure for large scale production of bio-fertilizers

National Fertilizers limited Company

National Fertilizers Limited (NFL) (A Government of India Undertaking) is producing biofertilizers and the company made record production & dispatches of Bio-fertilizers of 567 MT & 619 MT respectively against previous best of 506 MT (2014-15) & 605 MT (2013-14) respectively. 530 MT of Bio-fertilizers valuing 3.01 crore was sold during 2015-16 (annual report of NFL, 2016). Some products of this company are as shown in table (Source NFL)

Niku Bio-Research Lab

The Niku Bio Res.Lab.was established in the year 1997 at 613, Nana Peth, Pune. The name itself signifies N=Natural, I=Input, K=Complete and U=Utilisation. In short Niku means complete utilization of natural inputs for enhancement of crop yields. Table         shows types of bio-fertilizers presentally produced by the laboratory (Source Niku Bio- Research Lab)

References

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Deepali and Gangwar, K.K. (2013) Biofertilizers: an eco-friendly way to replace chemical fertilizers. Krishiseva

Farmer, B. H. (1986). “Perspectives on the ‘Green Revolution’in South Asia”. Modern Asian Studies. 20 (01): 175–199. doi:10.1017/s0026749x00013627.

Ghosh, N. (2004) Promoting Bio-Fertilizers in Indian Agriculture, Research Project conducted at the Institute of Economic Growth for Ministry of Agriculture.

Hazell and Peter B.R. (2009). The Asian Green Revolution.IFPRI Discussion Paper. Intl Food Policy Res Inst. GGKEY:HS2UT4LADZD.

Mohaparta, B., Verma, D.K., Sen, A., Panda, B.B. and Asthir, B. (2013). Bio-fertilizers- a gateway to sustainable agriculture. Popular Kheti 1(4):97-106

Vance, C.P. (1998). Legume symbiotic nitrogen fixation: agronomic aspects, In H.P. Spaink, A. Kondorosi, and P.J.J. Hooykaas (eds.), The Rhizobiaceae (pp. 509-530). Dordrecht, the Netherlands: Kluwer Academic Publishers.

Vijayapriya, M. and Muthukkaruppan, S.M. (2010) Isolation and Screening of Silicate Solubilizing Bacteria and Its Biocontrol Nature against Pyricularia oryzae. International Journal of Recent Scientific Research, 4, 87-91.