Bio-fertilizers: classification and characteristics

Introduction

• Modern sustainable agriculture focuses on improving productivity while maintaining soil health and minimizing environmental pollution.
• Bio-fertilizers play a vital role in this by enhancing nutrient availability to crops through biological processes.

Definition

• Bio-fertilizers are living microorganisms which, when applied to seed, plant surface, or soil, promote plant growth by increasing the availability or supply of primary nutrients to the host plant.
• According to the National Project on Organic Farming (NPOF, India):
• “Bio-fertilizers are products containing carrier-based (solid or liquid) living microorganisms which are agriculturally useful in terms of nitrogen fixation, phosphorus solubilization, or nutrient mobilization.”

Importance of Bio-fertilizers

• Enhance soil fertility through biological nitrogen fixation, phosphorus solubilization, and mobilization of nutrients.
• Reduce dependence on chemical fertilizers.
• Improve soil microbial activity and soil structure.
• Promote eco-friendly and sustainable farming.
• Cost-effective and safe for the environment.
• Increase nutrient uptake and crop yield naturally.

Mechanism of Bio-fertilizers

Bio-fertilizers act through various mechanisms:

• Biological Nitrogen Fixation (BNF) – Conversion of atmospheric N₂ into plant-usable form (NH₃).
• Phosphorus Solubilization – Conversion of insoluble P (like rock phosphate) into soluble forms.
• Phosphorus Mobilization – Mycorrhizal fungi help in mobilizing P from deeper soil layers.
• Production of Growth Hormones – Indole acetic acid (IAA), gibberellins, cytokinins.
• Decomposition of Organic Matter – Enhances nutrient release.
• Disease Suppression – By producing antibiotics or competing with pathogens.

Classification of Bio-fertilizers

• Bio-fertilizers are classified based on the type of nutrient they fix or mobilize, and the microorganisms involved.
• Nitrogen-Fixing Bio-fertilizers

• Phosphorus-Solubilizing and Mobilizing Bio-fertilizers

• Bio-fertilizers for Other Nutrients

Plant Growth-Promoting Rhizobacteria (PGPR)

• Include beneficial bacteria that colonize the rhizosphere and promote plant growth through:
  • Nutrient solubilization.
  • Hormone production (IAA, GA, Cytokinins).
  • Antagonism against pathogens.
  • Stress tolerance.

Examples: Pseudomonas fluorescens, Bacillus subtilis, Serratia marcescens.

• Organic Waste Decomposers

6. Characteristics of an Efficient Bio-fertilizer

An ideal bio-fertilizer should possess the following qualities:

• High microbial population (at least 10⁷–10⁹ viable cells/g or ml).
• Strain specificity to particular crops or soil conditions.
• High survival rate under storage and field conditions.
• Non-toxic and eco-friendly to plants, animals, and humans.
• Quick establishment and multiplication in the rhizosphere.
• Compatibility with fertilizers and pesticides.
• Efficient nutrient fixation or solubilization ability.
• Longer shelf life (preferably 6–12 months).
• Carrier material should maintain microbial viability (e.g., peat, lignite, charcoal).
• Easy application (seed treatment, soil application, or root dipping).

7. Forms of Bio-fertilizers

1. Methods of Application

1. Advantages of Bio-fertilizers

• Improve soil fertility and structure.
• Reduce chemical fertilizer requirement by 25–50%.
• Increase yield by 10–30%.
• Maintain soil microbial balance.
• Reduce greenhouse gas emissions.
• Enhance soil organic carbon and water-holding capacity.
• Support sustainable and organic farming systems.

1. Limitations

• Require proper storage and handling.
• Sensitive to high temperature and sunlight.
• Effectiveness depends on soil type, pH, and moisture.
• Slower in response compared to chemical fertilizers.
• Specific to crops and ecological conditions.

1. Examples of Commercial Bio-fertilizer Products in India