Organic and small farmers over chemical fertilizers. Potential Characteristic

Organic
farming has emerged as an important priority area globally in view of the
growing demand for safe and healthy food and long term sustainability and
concerns on environmental pollution associated with indiscriminate use of
agrochemicals. Though the use of chemical inputs in agriculture is inevitable
to meet the growing demand for food in world, there are opportunities in
selected crops and niche areas where organic production can be encouraged to
tape the domestic export market. Bio-fertilizers are being essential component
of organic farming are the preparations containing live or latent cells of
efficient strains of nitrogen fixing, phosphate solubilizing or cellulolytic
micro-organisms used for application to seed, soil or composting areas with the
objective of increasing number of such micro-organisms and accelerate those
microbial processes which augment the availability of nutrients that can be
easily assimilated by plants. Biofertilizers play a very significant role in
improving soil fertility by fixing atmospheric nitrogen, both, in association
with plant roots and without it, solubilize insoluble soil phosphates and
produces plant growth substances in the soil. They are in fact being promoted
to harvest the naturally available, biological system of nutrient mobilization
(Venkatashwarlu, 2008). The role and importance of bio-fertilizers in
sustainable crop production has been reviewed by several authors. But the
progress in the field

 of BF production technology remained always
below satisfaction in Asia because of various constraints.

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Need
of Bio-Fertilizers

Indiscriminate
use of synthetic fertilizers has led to the pollution and contamination of the
soil, has polluted water basins, destroyed micro-organisms and friendly
insects, making the crop more prone to diseases and reduced soil fertility.
Demand is much higher than the availability. It is estimated that by 2020, to
achieve the targeted production of 321 million tones of food grain, the
requirement of nutrient will be 28.8 million tones, while their availability
will be only 21.6 million tones being a deficit of about 7.2 million tones1.
Depleting feedstock/fossil fuels (energy crisis) and increasing cost of
fertilizers. This is becoming unaffordable by small and marginal farmers,
depleting soil fertility due to widening gap between nutrient removal and
supplies, growing concern about environmental hazards, increasing threat to
sustainable agriculture. Besides above facts, the long term use of
bio-fertilizers is economical, eco-friendly, more efficient, productive and
accessible to marginal and small farmers over chemical fertilizers.

Potential
Characteristic features of some bio-fertilizers Nitrogen fixers

Rhizobium:
It is belongs to family Rhizobiaceae, symbiotic in
nature, fix nitrogen 50-100 kg/ ha in association with legumes only. It is
useful for pulse legumes like chickpea, red-gram, pea, lentil, black gram,
etc., oil-seed legumes like soybean and groundnut and forage legumes like berseemand
lucerne. Successful nodulation of leguminous crops by Rhizobium largely
depends on the availability of compatible strain for a particular legume. It
colonizes the roots of specific legumes to form tumor like growths called root
nodules, which acts as factories of ammonia production. Rhizobium has
ability to fix atmospheric nitrogen in symbiotic association with legumes and
certain non-legumes like Parasponia. Rhizobium population
in the soil depends on the presence of legume crops in the field. In absence of
legumes, the population decreases. Artificial seed inoculation is often needed
to restore the population of effective strains of the Rhizobium near the
rhizosphere to hasten N-fixation. Each legume requires a specific species of Rhozobiumto
form effective nodules.

Azospirillum:It
isbelongs to family Spirilaceae, heterotrophic and associative in
nature. In addition to their nitrogen fixing ability of about 20-40 kg/ha, they
also produce growth regulating substances. Although there are many species
under this genus like, A.amazonense, A.halopraeferens, A.brasilense,
but, worldwide distribution and benefits of inoculation have been proved mainly
with the A.lipoferumand A.brasilense. The Azospirillumform
associative symbiosis with many plants particularly with those having the
C4-dicarboxyliac path way of photosynthesis (Hatch and Slack pathway), because
they grow and fix nitrogen on salts of organic acids such as malic, aspartic
acid. Thus it is mainly recommended for maize, sugarcane, sorghum, pearl millet
etc. Azotobacter colonizing the roots not only remains on the root surface but
also a sizable proportion of them penetrates into the root tissues and lives in
harmony with the plants. They do not, however, produce any visible nodules or
out growth on root tissue.

Azotobacter:It
isbelongs to family Azotobacteriaceae, aerobic, free living, and
heterotrophic in nature. Azotobacters are present in neutral or alkaline
soils and A. chroococcumis the most commonly occurring species in arable
soils. A. vinelandii, A. beijerinckii, A. insignis and A.
macrocytogenesare other reported species. The number of Azotobacterrarely
exceeds of 104 to 105 g-1 of soil due to lack of organic matter and presence of
antagonistic microorganisms in soil. The bacterium produces anti-fungal
antibiotics which inhibits the growth of several pathogenic fungi in the root
region thereby preventing seedling mortality to a certain extent. The
population of Azotobacteris generally low in the rhizosphere of the crop
plants and in uncultivated soils. The occurrence of this organism has been
reported from the rhizosphere of a number of crop plants such as rice, maize,
sugarcane, bajra, vegetables and plantation crops.

Blue
Green Algae (Cyanobacteria) andAzolla:These belongs to eight
different families, phototrophic in nature and produce Auxin, Indole acetic
acid and Gibberllic acid, fix 20-30 kg N/ha in submerged rice fields as they
are abundant in paddy, so also referred as, paddy organisms?. N is the key
input required in large quantities for low land rice production. Soil N and BNF
by associated organisms are major sources of N for low land rice. The 50-60% N
requirement is met through the combination of mineralization of soil organic N
and BNF by free living and rice plant associated bacteria. To achieve food
security through sustainable agriculture, the requirement for fixed nitrogen
must be increasingly met by BNF rather than by industrial nitrogen fixation.
BGA forms symbiotic association capable of fixing nitrogen with fungi,
liverworts, ferns and flowering plants, but the most common symbiotic association
has been found between a free floating aquatic fern, the Azolla and Anabaena
azollae(BGA). Azollacontains 4-5% N on dry basis and 0.2-0.4% on wet
basis and can be the potential source of organic manure and nitrogen in rice
production. The important factor in using Azollaas bio-fertilizer for
rice crop is its quick decomposition in the soil and efficient availability of
its nitrogen to rice plants. Besides N-fixation, these biofertilizers or
biomanures also contribute significant amounts of P, K, S, Zn, Fe, Mb and other
micronutrient. The fern forms a green mat over water with a branched stem,
deeply bilobed leaves and roots. The dorsal fleshy lobe of the leaf contains
the algal symbiont within the central cavity. Azolla can be applied as green
manure by incorporating in the fields prior to rice planting. The most common
species occurring in India is A. pinnataand same can be propagated on
commercial scale by vegetative means. It may yield on average about 1.5 kg per
square meter in a week. India has recently introduced some species of Azolla
for their large biomass production, which are A.caroliniana, A. microphylla,
A. filiculoides and A. mexicana.

Phosphate
solubilizers: Several reports have examined the ability of different
bacterial species to solubilize insoluble inorganic phosphate compounds, such
as tri-calcium phosphate, di-calcium phosphate, hydroxyapatite, and rock
phosphate. Among the bacterial genera with this capacity are pseudomonas,
Bacillus, Rhizobium, Burkholderia, Achromobacter, Agrobacterium, Microccocus,
Aereobacter, Flavobacteriumand Erwinia. There are considerable
populations of phosphatesolubilizing bacteria in soil and in plant
rhizospheres. These include both aerobic and anaerobic strains, with a
prevalence of aerobic strains in submerged soils. A considerably higher
concentration of phosphate solubilizing bacteria is commonly found in the
rhizosphere in comparison with non rhizosphere soil. The soil bacteria
belonging to the genera Pseudomonas and Bacillus and Fungi are
more common.

Phosphate
absorbers (Mycorrhiza): The term Mycorrhiza denotes “fungus
roots”. It is a symbiotic association between host plants and certain group of
fungi at the root system, in which the fungal partner is benefited by obtaining
its carbon requirements from the photosynthesis of the host and the host in
turn is benefited by obtaining the much needed nutrients especially phosphorus,
calcium, copper, zinc etc., which are otherwise inaccessible to it, with the
help of the fine absorbing hyphae of the fungus. These fungi are associated
with majority of agricultural crops, except with those crops/plants belonging
to families of Chenopodiaceae, Amaranthaceae, Caryophyllaceae, Polygonaceae,
Brassicaceae, Commelinaceae, JuncaceaeandCyperaceae.

Zinc
solubilizers: The nitrogen fixers like Rhizobium,
Azospirillum, Azotobacter, BGA and Phosphate solubilizing bacteria like B.
magaterium, Pseudomonas striata, and phosphate mobilizing Mycorrhiza have
been widely accepted as bio-fertilizers. However these supply only major
nutrients but a host of microorganism that can transform micronutrients are
there in soil that can be used as bio-fertilizers to supply micronutrients like
zinc, iron, copper etc.,The zinc can be solubilized by microorganisms viz., B.
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 or in soils where native zinc is higher or in
conjunction with insoluble cheaper zinc compounds like zinc oxide (ZnO), zinc
carbonate (ZnCO3) and zinc sulphide (ZnS) instead of costly zinc sulphate.

Potential role
of bio-fertilizers in agriculture

The incorporation
of bio-fertilizers (N-fixers) plays major role in improving soil fertility,
yield attributing characters and thereby final yield has been reported by many
workers. In addition, their application in soil improves soil biota and
minimizes the sole use of chemical fertilizers. Under temperate conditions,
inoculation of Rhizobium improved number of pods plant-1, number of seed
pod-1 and 1000-seed weight (g) and thereby yield over the control. The number
of pods plant-1, number of seed pod-1 and 1000-seed weight. In rice under low
land conditions, the application of BGA+ Azospirillumproved
significantly beneficial in improving LAI and all yield attributing aspects.

It
is an established fact that the efficiency of phosphate fertilizers is very low
(15-20%) due to its fixation in acidic and alkaline soils and unfortunately
both soil types are predominating in India accounting more than 34% acidity
affected and more than seven million hectares of productively and
salinity/alkaline affected. Therefore, the inoculations with PSB and other
useful microbial inoculants in these soils become mandatory to restore and
maintain the effective microbial populations for solubilization of chemically
fixed phosphorus and availability of other macro and micronutrients to harvest
good sustainable yield of various crops.

Effect of Azospirillumand
Azotobacterinoculation on the growth, yield and quality of vegetables:

Plant
height and biological yield have been affected significantly by co-inoculation
followed by single inoculation because this biofertilizer can enhance absorbed
of nitrogen by plant. Thus, it can be said that for obtaining maximum grain
yield as well as profit from tomato, soil should be inoculated with Azotobacter
with Azospirillum (Ramakrishnan and Selvakumar,2012). Seed treatment with
Azotobacter in okra not only reduced the nitrogen dose through inorganic
sources but enhances the overall productivity and production levels both in
terms of fruit as well as seed yield (Bhusanet
al.,2013).Gupta et al.,(2010)
reported that Both the inoculants i.e.Azospirillum
and Azotobacter in combination with 75% chemical nitrogen recorded highest
values for all the parameters whereas B1N1 (Azospirillum + 50% R.D.F) affects
yield contributing traits like bulb weight, bulb diameter, bulb volume which
ultimately affected the yield were increased by the application saving 25% of
nitrogen.Azospirillum inoculation not only improved yield and nutritional value
but also extended storage life and product quality in lettuce grown under salt
stress and explore the possibility of establishing nurseries and/or growing
vegetables in world regions where the salt limits the production (Fasciglioneet al.,2015).

Azospirillum
spp.
and Azotobacter spp. favored the growth and yield of crop under
hydroponic strawberry in comparison the witness even when the nutrients of leaf
did not differ on a large scale.

spinach seed inoculation with 300 g phosphorein in
the presence of 100% N (full recommended nitrogen dose) plus 66.7 or 33.3% of
the recommended P2O5 dose, or with 300 g Azotobacter in
the presence of 100% P (full recommended P2O5 dose) + 50%
of the recommended nitrogen dose significantly increased plant growth and seed
yield with best quality. Bio-fertilizers can partially substitute chemical
fertilizers, which could reduce production coast and subsequently environmental
pollution load (Assioutyet al.,2005).
Azospirrilium and Azotobactor improved yield, nutritional
value, extended storage life partially substitute chemical fertilizers, which
could reduce production coast and subsequently environmental pollution load.

Effect of VAM (Vesicular Arbuscular
Mycorrhizae) inoculation on the growth, yield and quality of vegetables:

AMF colonized with several cereal, vegetables,
fruits and industrial crops. Among the species studied, G. mosseae showed
better colonization and improved plant growth, yield, nutrient uptake, water
use efficiency and disease resistance. However, mycorrhizae exhibited better performance
in low P added soil(Naheret al.,2013).
The application of biofertilizer containing beneficial microbes showed
promoting effect on the growth and improvement of nutrient properties on tomato
seedlings through a 40-day field study. The inoculation with VAM fungi can
significantly increase the root mycorrhizal dependency. The presence of mycorrhizal
fungi had different influence on the population of G. fasciculatum and G.
intraradiceswas able to stimulate the introduced beneficial bacterial
growth and mycorrhizal dependency in the rhizosphere soil (Ramkrishnan and
Selvakumar,2015). Nutrients (Ca, K, Mg, P, Fe and S and Si) uptakes of
cowpea (V. unguiculata) varieties
showed that varieties and the effect of treatments were significantly
different. Maximum uptake of nutrient was attained in mycorrhizal plants. Our
results are supported by the Singh et al. (2004), Sharma (2004)andGhazala
(2005) who reported that nutrient uptake of mycorrhizal plants was higher when
compared with non-mycorrhizal one. One of the most dramatic effects of
mycorrhizal infection on the host plant is the increase in phosphorus. AMF have
been shown to improve immobile nutrients uptake such as P, Zn and Cu (George
2000, Liu et al., 2002). Mycorrhizal fungi can also improve absorption
of phosphorus (Kalipada and Singh, 2003) potassium (Liu et al., 2002),
magnesium (Liu et al., 2002), copper (George, 2000), zinc (Jamal et al., 2002,
Habte and Osorio, 2002, Chen et al., 2003) and calcium (Liu et al.,
2002). AMF Glomus mosseae Mycorrhizal colonization was higher in
the control than in saline soil conditions. Shoot and root dry matter yields
and leaf area were higher in mycorrhizal than in nonmycorrhizal plants. Total
accumulation of P, Zn, Cu, and Fe was higher in mycorrhizal than in nonmycorrhizal
plants under both control and medium salt stress conditions. Shoot Na
concentrations were lower in mycorrhizal than in nonmycorrhizal plants grown
under saline soil conditions. The improved growth and nutrient acquisition in
tomato demonstrate the potential of AMF colonization for protecting plants
against salt stress in arid and semiarid areas(Karaki,2000).  Arbuscularmycorrhizal
fungi Glomus monosporum, G. vesiculiferum, G. deserticola, G. intraradices, G. mosseaeshowed their effect on plant
growth and fruit production of tomato (Lycopersiconesculentum Mill.) cv. Trust inoculated with Fusariumoxysporum f. sp. radicis-lycopersici (FORL) under near-commercial
greenhouse conditions. Inoculation with G.
monosporum and G. mosseae significantly increased fruit yield
and fruit number of tomato plants grown hydroponically in sawdust. Plant height
and plant dry weight increased significantly when inoculated with G. monosporum and G.
mosseae. Further, plants inoculated with G.
monosporum and G. mosseae showed significantly lower forl root
infection than the untreated control plants(Utkhede,2006).AM inoculation also
significantly increased shoot dry matter and the number of flowers and fruits.
The fruit yields of M+ plants under severe, moderate, mild drought-stressed
conditions were higher. Furthermore, M+ plants produced tomato fruits that
contain significantly higher quantities of ascorbic acid and total soluble
solids (TSS) than M? plants. Mycorrhizal effects increased with increasing
intensity of drought. The overall results suggest that mycorrhizal colonization
affects host plant nutritional status, water stratus and growth under field
conditions and thereby alters reproductive behavior, fruit production and
quality of fruits under both well-watered and drought-stressed
conditions(Subramanian,2006).Mycorrhizal colonization is common in tomato
plants and well documented as a mycotrophic plant (Kubota et al.,2005).
Mycorrhizal inoculation was also beneficial for lady’s finger (Abelmoschus esculentus). And showed
growth and yield improvement of lady’s finger with mycorrhizal inoculation. G.
mosseae was able to colonize lady’s finger and showed a synergistic effect with
plant growth promoting rhizobacterial (PGPR) isolate UPMB10 (Radziahet al.,
2007). A significant increase in plant biomass, yield and zinc uptake of lady’s
finger was observed with microbial inoculation. AMF have been observed to
improve growth of brinjal (Solanum melongena L.) and showed that
application G. intraradices on
brinjalseedling, significantly affected the shoot length, shoot diameter,
number of leaves, shoot fresh weight, shoot dry weight, root fresh weight and
root dry weight.

Conclusion                                      

Bio-fertilizers
being essential components of organic farming play vital role in maintaining
long term soil fertility and sustainability by fixing atmospheric di-nitrogen
(N=N), mobilizing fixed macro and micro nutrients or convert insoluble P in the
soil into forms available to plants, there by increases their efficiency and
availability. Currently there is a gap of ten million tones of plant nutrients
between removal of crops and supply through chemical fertilizers. In context of
both the cost and environmental impact of chemical fertilizers, excessive
reliance on the chemical fertilizers is not viable strategy in long run because
of the cost, both in domestic resources and foreign exchange, involved in
setting up of fertilizer plants and sustaining the production. In this context,
organic manures (bio-fertilizers) would be the viable option for farmers to
increase productivity per unit area.