BIOFERTILIZER - AN INTRODUCTION

 BIOFERTILIZERS

• Generally, the term "Fertilizer" is used for "Fertilizing material or Carrier", meaning any substance which contains one or more of the essential elements (nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, iron, manganese, molybdenum, copper, boron, zinc, chlorine, sodium, cobalt, vanadium and silicon). Thus, fertilizers are used to improve the fertility of the land.
• Biofertilizers may be defined as “Substances which contains living strains of microorganisms (bacteria, fungi and algae) that colonize the Rhizosphere or the interior of the plants and promote growth by increasing the supply or availability of primary nutrients to the target crops, when applied to soils, seeds or plant surfaces”.
• Biofertilizers infuse nutrients by natural processes such as synthesis of growth promoting substances, fixing atmospheric nitrogen and solubilizing insoluble nutrients in the Rhizosphere.

Need of Biofertilizers

• In recent years, it is being noticed that excessive exposure to chemical fertilizers and pesticides which not only deteriorate soil health but also create several environmental impacts as global threat.
• Increasing application of chemical fertilizers in agriculture make country self dependent in food production but it depreciates environment and cause harmful impacts on living beings.  
• The heavy use of synthetic fertilizers for past many decades has led to depletion of essential nutrients from soil, contamination of the soil with harmful and non-degradable substances, pollution of water resources and destruction of friendly insects and essential microorganisms from the soil.
• The global demand for fertilizers is much higher than the availability.
• The costs of chemical fertilizers are also increasing every other day, making them unaffordable by marginal and small farmers. 

Types of Biofertilizers

I) Nitrogen fixers

• Free living or Asymbiotic or Non – symbiotic Nitrogen fixers

1. Aerobic Heterotrophs– Azotobacter sp., Achromobacter sp.  & Beijerinckia sp.
2. Aerobic Autotrophs– Nostoc sp., Anabaena sp., Colothrix sp. and Blue Green Algae (BGA).
3. Anaerobic Heterotrophs – Clostridium sp., Klebsiella sp. and Desulfovibrio sp.
4. Anaerobic Autotrophs – Chlorobium sp., Chromnaticum sp., Rhodospirillum sp. and Methanobacterium sp.

• Symbiotic Nitrogen fixers – Rhizobium sp., Bradyrhizobium sp., Azhorhizobium sp., Frankia sp., Blue Green Algae and Anabaena azollae.
• Associative symbiotic Nitrogen fixers – Azospirillum sp. and Herbaspirillum sp.
• Endophytic Nitrogen fixers – Gluconacetobacter sp. and Burkholderia sp.

II) Phosphorous solubilizers

• Bacteria – Bacillus megaterium var phosphaticum, Bacillus subtilis, Bacillus circulans, Bacillus polymyxa and Pseudomonas striata.
• Fungi – Aspergillus awamori and Penicillium sp.

III) Phosphate mobilizers

• Arbuscular mycorrhiza (AM) – Glomus sp., Gigaspora sp., Acaulospora sp., Scutellospora sp. and Sclerocystis sp.
• Ectomycorrhiza – Laccaria sp., Pisolithus sp., Boletus sp. and Amanita sp.
• Ericoid mycorrhiza – Pezizella ericae
• Orchid mycorrhiza – Rhizoctonia solani

IV) Potassium mobilizers – Frateuria aurentia

V) Silicate and Zinc solubilizers – Bacillus sp.

VI) Manganese solubilizers – Penicillium citrinum

VII) Silicate solubilizers – Bacillus mucilaginous

VIII) Plant Growth Promoting Rhizobacteria (PGPR)

Benefits of Biofertilizers

• Eco-friendly
• Protect the environment from pollutants since they are natural fertilizers.
• Cost-effective.
• Restore soil nature fertility.
• Improve soil texture and yield of plants (20 to 30 %).
• Activates soil biologically.
• Fix atmospheric nitrogen in the soil and root nodules of legume crops and make it available to the plant.
• Solubilise the insoluble forms of phosphates like tricalcium, iron and aluminium phosphates into available forms.
• Scavenge phosphate from soil layers.
• Replace chemical nitrogen and phosphorous by 25 %.
• Produce phytohormones and antimetabolites which promote root growth.
• Destroy many Phytopathogens present in the soil.
• Provides resistance against high temperature, salinity and drought.
• Proved to be effective even under semi-arid conditions.
• Decompose organic matter and help in mineralization in soil.
• When applied to seed or soil, biofertilizers increase the availability of nutrients and improve the yield by 10 to 25 % without adversely affecting the soil and environment.

Caution in the use of Biofertilizers

• Biofertilizer packets need to be stored in cool and dry place away from direct sunlight and heat.
• Never mix biofertilizers with fungicides and other chemicals.
• Do not keep used solution overnight.
• Right combinations of biofertilizers have to be used.
• As Rhizobium is crop specific, one should use for the specified crop only.
• While purchasing one should ensure that each packet is provided with necessary information like name of the product, name of the crop for which intended, name and address of the manufacturer, date of manufacture, date of expiry, batch number and instructions for use.
• The packet has to be used before its expiry, only for the specified crop and by the recommended method of application.
• It is important to use biofertilizers along with chemical fertilizers and organic manures.
• Biofertilizers are not replacement of fertilizers but can supplement plant nutrient requirements.

Limitations of Biofertilizers

• Unavailability of suitable strain due to lack of availability of specific strain.
• Unavailability of suitable carrier.
• Lack of awareness among farmers.
• Inadequate human resources and inexperienced staff.
• Soil characteristics like salinity, acidity, drought; water logging affects the use of biofertilizers.