review article on biofertilizers

Review ABSTRACT: One of the challenges of globalization to developing countries is to increase agricultural production quantitatively but also to improve the quality of the product so that it can go well in the world market. Agrochemicals responsibible for making India self sufficient through Green revolution are no longer able to sustain the productivity to the extent on account of all the ill-effects it had on the agro system during the process. Biofertilizers i.e. Biological Based Product are most advanced biotechnology necessary to support developing organic agriculture sustainable agriculture, green agriculture and non-pollution agriculture.

1. Introduction: During the past four decades we have witnessed doubling of human population and a concurrent doubling of food production. On the contrary we have entered the third millennium with more than a billion people and we are facing a Herculean task of providing food to this rapidly increasing population particularly in developing country like India [Dhaliwal And Arora, 2003].(2) To cope up with the need of increasing the agricultural productivity in accordance with the population and to improve the quality of the product in terms of nutritional value has resulted in misuse and excessive use of chemical fertilizer. Poorly managed use of these chemical N and P fertilizers have created several environmental problems such as deterioration of soil quality, leaching, acidification ,denitrifiction,air pollution, reduced biodiversity, disrupting the fragile ecosystem.(1,2). Thereby to overcome these ecological problems, to minimize the use of chemical fertilizers we are now directing ourselves towards the potential use of ecofreindly approaches such as the use of Biofertilizers and Biopesticides to sustain high production, allow more efficient nutrient utilization and thereby provide solutions for present and future agricultural practices. In this review article a brief overview on the potential use of 1

“Biofertilizer”a Biological Based Product as an alternative for sustainable agriculture is being discussed.

2)What are Biofertilizers? Biofertilizers are natural and organic fertilizers.Biofertilizers are preparations containing cells of microorganisms which may be nitrogen fixers, phosphorus solublizers, sulphur oxidizers or organic matter decomposers. They are called as bioinoculants-bacterium or fungi which on supply to plant improve their growth and yield. (13) These bioinoculants can reside on the surface of the plant or form endophytic association or else interacts with other microbes in the rhizosphere or phyllosphere thereby influencing the plant growth. Production of chemical fertilizers require fossil fuel energy while microbes do not thereby proving to be cost effective ecofreindly with the simple methodology of production and thereby no hazard to the agro ecosystem(13,10) Biofertilizers thereby might assume a special significance towards development of strategies for improving productivity and economizing the production cost, minimizing our dependence on synthetic chemical fertilizers. Let us move towards a more comprehensive description of microbial biofertilizers. The most limiting nutrient for plant growth are Nitrogen(N) and Phosphorus(P).Some microorganisms used as Biofertilizers fix atmospheric Nitrogen and while others increase availability and uptake of nutrients such as ‘P’and other key micronutrients such as copper,manganese,molybdenum etc.Thereby these Biofertilizers increase the crop yield tremendously.

3] N2 Fixing Bacteria as Microbial Biofertilizers: Air consists of approximately 80% nitrogen gas (N2), representing about 6400 kg of N above every hectare of land. However, N2 is a inert, stable gas, normally unavailable to 2

plants. Although abundant and ubiquitous in the air Nitrogen is the most limiting nutrient for plant growth because the atmospheric N is in the most stable form and is therefore not available for plant uptake. Most of N is tied up in soil organic matter. Symbiotic and nonsymbiotic microorganisms have the ability to fix N2 and convert it into NH4+, a form that can be easily absorbed by plants. These organisms convert the atmospheric Nitrogen into ammonia and amino acids which can then be used up by plants to build up proteins. This process is known as “Biological Nitrogen Fixation”. (11) The close proximity of these microorganisms to their host plants allows efficient of fixed N. These bacteria capable of N2 fixation are of following types:1) There are many free living N2 fixing bacteria in soil. 2) Some have adapted to symbiosis; intimate endophytic association with plants. 3) Some live in close association in the plant root zone (rhizosphere) without forming intimate endophytic symbiosis. Let us evaluate their use as biofertilizers. I) Symbiotic N2 fixers: (1) Rhizobia:The best known and most exploited symbiotic N2 fixing bacteria belonging to family Rhizobiacea include the genera such as Rhizobium, Bradyrhizobium etc.These bacteria infect legumes and have global distribution. However N2 fixing capability of Rhizobia varies greatly depending on the host plant species. Therefore selection of best strains must take Rhizobia host compatibility for selection of Biofertilizers. (13, 11) Legumes (such as beans, soybean, chickpea) inoculation is an old practice that has been carried out especially when local/resident rhizobial population in the soil are low.Rhizobial inoculum can be produced and applied in numerous ways such as granular, liquid or powder formulation. (11) However the success depends upon strain and environmental condition. Therefore it is essential to evaluate inoculation programme, type depending on field experiments, microbiological assays and cost benefit analysis. 3

2) Frankia: Frankia is the genus of N2 fixing actinomyctes capable of fixing N2 similar to rhizobial symbiosis. Frankia can fix N2 at normal O2 concentration at the rate sufficient to support its growth N2 fixation is accompanied by the development of terminal swelling known as vesicles in which nitrogenase enzyme are protected by restrictingO2diffusion. In addition to symbiotic properties of strain characteristics such as age of the inoculum cellular concentration and the method of preservation greatly effect the inoculum infectivity. (11) Since a universal strain adapted to different environmental host genotype does not exist, best plant Frankia combination should be selected and customized for a target area and target species. 3) Cyanaobacteria: Cyanaobacteria are ecologically important in N2 fixing organisms especially in rice cultivation. Anabaena azollae is a symbiotic heterocyst nitrogen fixing Cyanaobacteria which lies in fronds in the pores of the Azolla.(6) Contribution of the Cyanaobacteria to Total N uptake by rice seedlings was assessed using free-living and immobilized A.azollae in the presence of different combined Nitrogen sources using 15 N dilution technique.(6)

Methods(6) The cyanobiont Anabaena azollae(AS-DS )is grown in N free BG-11 medium azollae immobilized on Polyurethene(PUF) and Sugarcane waste(SCW) was used for this study. 30 days grown free living and immobilized Cyanaobacterial culture were used as inoculants. A Paddy seed (cultivar ADT36) were soaked for 12 hours in water and was later on allowed to sprout. The freely living and immobilized A.azollae were then inoculated in Nfree medium at 500 mg fresh weight Cyanaobacterial biomass along with sprouted seeds. The combined N2 in the form of urea, potassium nitrate and ammonium sulphate with 10% atom excess 15N was added at to the growth medium at weekly intervals. After 30 days rice seedling were dried, powdered, total N was determined by micro-Kjeldahl digestion and distillation method and Mass spectrometry.

4

The percent N derived from combined nitrogen source ( %Ndff) and percent N derived from Cyanaobacteria (%Ndfc) of total N content of rice seedlings were calculated using the formula. %Ndff=Atom percent excess 15 N in inoculated plant*100/Atom percent

15

N in uninoculated plant

%Ndfc=100-%Ndff Effect of inoculation of A.azollae (AS-DS)with different Combined Nitrogen on total N content and 15N recovery in rice seedlings. 15

Total N

N recovery

(mg plant) (atom excess %) Cyanaobacterial Combined N source Combined N source Contro Potassium urea NH4 Potassium urea NH4 culture

Free living

l

nitrate

1.2

3.9

5.9

SO4

nitrate

SO4

1.5

3.29

3

2.77 2.74

PUF immobilized

1.4

4.3

6.5

1.5

3.15

.89 3

SCW immobilized

1.4

4.6

7.8

2.3

2.96

.82 3

2.75

4.69

.69 4

3.11

Uninoculated

0.6

3.9

3.5

Control Interaction(p