The Role of Azotobacter and Azospirillum as Biofertilizers in Agriculture

In modern agriculture, sustainable practices are gaining importance, and biofertilizers like Azotobacter and Azospirillum are revolutionizing crop production. These free-living, nitrogen-fixing bacteria offer an eco-friendly alternative to chemical fertilizers, enhancing soil fertility and boosting crop yields. This article explores their benefits, applications, and factors affecting their effectiveness, making them a valuable asset for farmers worldwide.

What Are Azotobacter and Azospirillum?

Azotobacter and Azospirillum are high-quality, free-living, nitrogen-fixing bacteria that play a crucial role in enriching soil with nitrogen, an essential nutrient for plant growth. Unlike symbiotic bacteria, these microorganisms do not require a host plant to survive or fix nitrogen, making them versatile for various crops.

• Azotobacter: An aerobic bacterium, Azotobacter thrives in oxygen-rich environments. Its key species include Azotobacter chroococcum, A. vinelandii, and A. beijerinkia. It can fix approximately 10-15 kg of nitrogen per hectare per season, though it is sensitive to acidic soils (pH below 6.0) and waterlogged conditions. Interestingly, it can still function in paddy fields, likely due to oxygen released by algae or cyanobacteria in the soil.
• Azospirillum: Another free-living bacterium, Azospirillum includes important species like Azospirillum lipoferum and A. brasilense. It is particularly effective in lowland rice fields but is also recommended for upland crops. Its nitrogen-fixing capacity mirrors that of Azotobacter, with a minimum of 10⁸ microbial cells per gram required in commercial formulations.

Both biofertilizers can be applied to seedling roots or directly to the soil, benefiting a wide range of crops such as rice, wheat, maize, millet, mustard, sunflower, sugarcane, cotton, vegetables, and more.

Benefits of Using Azotobacter

1. Nitrogen Fixation: Azotobacter can supply plants with over 10 grams of nitrogen for every gram it consumes, significantly reducing the need for chemical fertilizers.

1. Plant Growth Hormones and Enzymes: Species like Azotobacter chroococcum secrete beneficial compounds such as thiamine, riboflavin, pyridoxine, cyanocobalamin, indole acetic acid (IAA), and gibberellic acid. These promote root development, flowering, and overall plant vigor.
2. Disease Protection: Azotobacter produces antifungal and antibacterial substances that control harmful pathogens like Alternaria and Helminthosporium, protecting crops naturally.
3. Increased Crop Yields: Studies show yield improvements with Azotobacter use—15.1% in wheat, 19.5% in maize, 15.1% in tomatoes, 6.3% in chilies, and 14% in rice.

Benefits of Using Azospirillum

1. Nitrogen Fixation: Certain strains of Azospirillum can fix 5-15 mg of nitrogen per gram of carbon assimilated, with top strains exceeding 10 mg. When applied to seeds or soil, it can contribute up to 25 kg of nitrogen per hectare.
2. Growth-Promoting Substances: Azospirillum releases plant hormones, enzymes, and vitamins that enhance root growth and nutrient uptake, leading to healthier plants.
3. Yield Enhancement: Field trials report a 6% increase in wheat yield and an impressive 17.3% boost in rice production with Azospirillum application.

Application Methods

• Seed Treatment: Mix 20 grams of biofertilizer per kg of seeds with 300-400 ml of water. Coat the seeds evenly and dry them in the shade before sowing.
• Seedling Root Treatment: Dissolve 1 kg of biofertilizer in 5-15 liters of water. Dip seedling roots in the solution for 25-30 minutes, drain, and transplant into the field.
• Soil Application: Combine 6 kg of biofertilizer per acre with 100 kg of organic manure and apply before irrigation. For crops like sugarcane or potatoes, split the dose into 3 kg at 30 days and 3 kg at 60 days.

Factors Affecting Effectiveness

The performance of Azotobacter and Azospirillum depends on several environmental and management factors:

• Soil pH: Azotobacter thrives at pH 6.0-7.4, while Azospirillum prefers 6.0-7.5. Acidic soils reduce their efficiency.
• Water Levels: Moist soils enhance activity, but waterlogging hampers both bacteria due to limited oxygen availability.
• Temperature: Optimal soil temperatures range from 20-35°C for Azotobacter.
• Chemical Inputs: High levels of chemical nitrogen fertilizers inhibit their growth, while pesticides like methyl parathion or malathion can destroy them. However, fungicides like carbendazim and mancozeb are generally safe.
• Soil Type: Azotobacter excels in sandy or loamy soils with low water retention, while Azospirillum suits clayey soils with good drainage.

When and Where to Use Them

Both biofertilizers are ideal for non-leguminous crops. Use Azotobacter in well-aerated, sandy soils and Azospirillum in clayey, moderately drained soils. In uncertain conditions with standing water (not wetlands), a 50:50 mix of both can be effective.

Also Check this part – The Effectiveness of Beneficial Microbial Fertilizers in Agriculture

Conclusion

Azotobacter and Azospirillum are powerful tools for sustainable farming, offering nitrogen fixation, growth promotion, and natural pest resistance. By reducing reliance on chemical fertilizers, they support eco-friendly agriculture while improving yields. Farmers can maximize their benefits by understanding soil conditions, application methods, and compatibility with other inputs. Embrace these biofertilizers to cultivate healthier crops and contribute to a greener planet.