Phosphobacteria

Introduction

Phosphobacteria are a functional group of beneficial soil bacteria that convert insoluble forms of phosphorus into plant-available forms. While phosphorus is abundant in most soils, it is often locked in mineral complexes, making it inaccessible to crops. Phosphobacteria help release this phosphorus naturally, reducing the need for chemical P fertilizers and improving nutrient use efficiency.

Scientific Description

Phosphobacteria refers broadly to multiple genera of phosphate-solubilizing bacteria (PSB), including Bacillus megaterium, Pseudomonas striata, Burkholderia, and Enterobacter. These microbes function by secreting organic acids (like gluconic acid, lactic acid) and enzymes (acid phosphatases) that break down bound phosphate compounds in the soil.

Mechanisms:

• Acidification: Release of organic acids that lower pH in the rhizosphere, releasing phosphorus from calcium, iron, and aluminum complexes.
• Chelation: Formation of chelates that bind metal ions and free phosphorus.
• Enzyme Secretion: Produces enzymes like phytases and phosphatases to break down organic P sources (e.g., phytate).
• Root Colonization: Many strains are also PGPR that stimulate root growth and enhance nutrient absorption.

Benefits

• Solubilizes Inorganic Phosphorus: Frees phosphorus from rock phosphate, tricalcium phosphate, and other insoluble forms.
• Enhances Root and Shoot Growth: Improved P uptake results in more vigorous plant growth and earlier flowering.
• Reduces Fertilizer Cost: Can reduce synthetic phosphorus requirement by 25–50% in many crops.
• Compatible with Other Inputs: Works well alongside Azospirillum, Rhizobium, Trichoderma, and mycorrhiza.
• Improves Soil Health: Boosts microbial diversity and nutrient turnover in the rhizosphere.

Uses

• Crops Benefited: Universally useful — rice, wheat, maize, pulses, oilseeds, vegetables, fruits, sugarcane, banana, plantation crops.
• Application Methods:
  • Seed treatment: 5–10 g/kg seed
  • Soil application: 2–4 kg/acre with compost or FYM
  • Seedling root dip: For vegetables and fruit saplings
  • Liquid drench: 5 mL/L water, especially in high P-fixation soils
• Ideal Conditions: Organic-rich soils with medium to low available P; effectiveness may drop in extremely acidic or alkaline soils

Trivia

• Phosphobacteria are often part of “NPK biofertilizer blends” used in integrated nutrient management.
• In some regions, phosphate rock is applied along with phosphobacteria to simulate slow-release phosphorus systems.
• PSB inoculation is especially beneficial in red and lateritic soils where P fixation is high.
• India’s ICAR and state agriculture departments have long promoted phosphobacteria use in rice, pulses, and sugarcane programs.