Biofertilizers

Biofertilizers are living organisms, mostly microorganisms like bacteria, fungi, algae, and actinomycetes, that enhance soil fertility and promote plant growth by fixing atmospheric nitrogen, decomposing organic matter, and making essential nutrients more available to plants. They offer a sustainable, environmentally friendly alternative to chemical fertilizers, helping in the long-term health of the soil and the environment.

1. Types of Biofertilizers; Biofertilizers can be categorized based on the nutrients they help in providing or the mechanisms they employ to improve plant growth. The major types are as follows:

a) Nitrogen-Fixing Biofertilizers; These biofertilizers contain microorganisms that can convert atmospheric nitrogen into a form that plants can utilize, making them an important source of nitrogen in soil, especially in nitrogen-deficient soils.

• i) Rhizobium: A symbiotic bacterium that forms nodules on the roots of leguminous plants (e.g., peas, beans, lentils). Action: It fixes nitrogen from the atmosphere and converts it into ammonia, which is then used by the plant. Use: Primarily for leguminous crops, as they have a symbiotic relationship with Rhizobium.
• ii) Azotobacter: A free-living nitrogen-fixing bacterium. Action: It fixes atmospheric nitrogen in the soil, providing it to non-leguminous plants. Use: Used in crops like cereals (wheat, maize), vegetables, and fruits.
• iii) Azospirillum: A nitrogen-fixing bacterium that lives on the roots of non-leguminous plants. Action: It fixes nitrogen in the soil and promotes plant growth by producing growth hormones like auxins. Use: Used on crops like maize, wheat, and sorghum.
• iv) Anabaena: A cyanobacterium (blue-green algae) found in rice paddies. Action: It helps in fixing nitrogen, which benefits paddy crops.

b) Phosphorus-Solubilizing Bio fertilizers; These biofertilizers contain microorganisms that convert insoluble forms of phosphorus into soluble forms, making it more available to plants.

• i) Phosphate-Solubilizing Bacteria (PSB): These bacteria solubilize fixed phosphorus in the soil by releasing organic acids like citric and lactic acid. Examples: Bacillus, Pseudomonas, Micrococcus.
• ii) Mycorrhizal Fungi (AMF): These fungi form a symbiotic relationship with plant roots, enhancing nutrient absorption. Action: Mycorrhizal fungi not only help plants absorb phosphorus but also provide protection from soil-borne diseases. Use: Applied to a variety of crops such as cereals, vegetables, and fruit trees.

c) Potassium-Solubilizing Biofertilizers; These biofertilizers contain microorganisms that release potassium from insoluble compounds in the soil, making it available for plant uptake.

• i) Bacillus mucilaginosus: A bacterium that solubilizes potassium from soil minerals like mica and feldspar. Action: Converts potassium into available forms for plants. Use: Applied to a wide range of crops.

d) Organic Matter-Decomposing Biofertilizers These biofertilizers contain microorganisms that break down organic material into humus, improving soil structure and nutrient content.

• i) Trichoderma spp.: A group of fungi used in soil to decompose organic matter and suppress soil-borne plant pathogens. Action: Decomposes organic material and acts as a biological control agent, protecting crops from diseases like root rot and wilt.
• ii) Vermicompost Bacteria and Fungi: These microorganisms are present in vermicompost, a product of the decomposition of organic materials by earthworms. Action: Enhance the breakdown of organic matter and improve soil fertility by adding beneficial microbes.

e) Plant Growth-Promoting Rhizobacteria (PGPR) These microorganisms help promote plant growth by producing growth hormones such as auxins, cytokinin, and gibberellins, as well as by outcompeting harmful pathogens.

• i) Pseudomonas spp. and Bacillus spp.: These bacteria promote plant growth through the production of growth-promoting substances. Action: Improve root development, enhance nutrient uptake, and provide protection from pathogens.
• ii) Enterobacter spp.: Known for promoting growth in both cereals and vegetables. Action: Enhance soil fertility by fixing nitrogen and producing growth hormones.

2. Methods of Application of Biofertilizers Biofertilizers can be applied in several ways depending on the type of microorganism, crop, and soil conditions.

Seed Treatment

• Coating: Biofertilizer is mixed with a binder (e.g., gum or clay) and coated onto seeds. This ensures that the microorganisms come into contact with the seed during germination.
• Soaking: Seeds are soaked in a solution of biofertilizer before sowing, ensuring that the microorganism attaches to the seed coat.

Soil Application

• Broadcasting: The biofertilizer is mixed with soil or compost and broadcasted on the soil surface before planting.
• Drilling: Biofertilizer is mixed with the seed and applied directly to the soil in a drill or planter. This ensures that microorganisms come in contact with the seed and root system.
• Furrow Application: Biofertilizers can be applied in the furrows during planting, especially for crops grown in rows.

Foliar Application

• Spraying: Biofertilizers are dissolved in water and sprayed directly onto the plant leaves. This is particularly effective for certain types of microorganisms like PGPR, which can be absorbed by the plant tissues through the leaves.

Irrigation Application (Fertigation)

• Drip Irrigation: Biofertilizers can be dissolved in water and applied through drip irrigation systems, allowing microorganisms to reach the root zone efficiently.
• Flood Irrigation: Biofertilizers can also be applied through conventional irrigation channels, especially in rice paddies.

Benefits of Biofertilizers

• Environmental Benefits
• Eco-friendly: Biofertilizers are natural products that do not harm the environment. Unlike chemical fertilizers, they do not cause water pollution or soil degradation.
• Sustainability: Biofertilizers contribute to sustainable agricultural practices by replenishing soil nutrients naturally, without depleting the soil or affecting its long-term health.

• Agronomic Benefits
• Improved Soil Health: By increasing organic matter and microbial activity, biofertilizers improve soil texture and fertility.
• Enhanced Nutrient Uptake: Biofertilizers help in the efficient uptake of essential nutrients such as nitrogen, phosphorus, and potassium.
• Improved Crop Growth: They enhance root development, which leads to better crop establishment and growth.
• Disease Resistance: Some biofertilizers, such as Trichoderma spp., act as biocontrol agents, suppressing soil-borne pathogens.
• Increased Yields: Biofertilizer-treated crops show improved yields due to enhanced nutrient availability, better disease resistance, and healthier plants.

• Economic Benefits
• Reduced Fertilizer Costs: Biofertilizers reduce the need for expensive chemical fertilizers, thereby lowering input costs for farmers.
• Higher Profits: With improved crop yields and reduced reliance on chemical fertilizers, farmers experience better profitability.
• Sustainability in Farming: Farmers can reduce dependence on synthetic fertilizers, contributing to the long-term health of their soils and reducing costs associated with soil degradation.

• Limitations of Biofertilizers
• Limited Shelf Life; Biofertilizers are living organisms, and their effectiveness diminishes over time. They require proper storage conditions, such as low temperature and humidity, to maintain their viability.
• Dependence on Environmental Conditions; Biofertilizers’ effectiveness is influenced by soil pH, temperature, moisture, and other environmental factors. For example, Rhizobium works best in soils with a neutral pH and sufficient moisture.