Microbial Mobilization of Soil Phosphorus and Sustainable P Management in Agricultural Soils

Phosphorus plays a vital role in maintaining soil fertility and securing global food supply by being crucial for plant, human and animal life. Globally phosphorus is mined from geological sediments and most of the mined P is added to agricultural soils to meet the critical need of crop plants for agronomic productivity. However, recovery of P by plants is abysmally low and major amount of added P is fixed in the soil creating a need for addition of P fertilizer. Microorganisms play a fundamental role in mobilizing inorganic and organic P in the soil and the rhizosphere. Wide variety of bacteria, fungi and endophytes solubilizes insoluble P through the production of organic acids, a feature which is genetically controlled and can be suitably manipulated to produce efficient transgenic strains. Plant inoculations with phosphate solubilizing microorganisms (PSMs) during field studies, however, had inconsistent effect on plant growth and crop yields due to variations in soil, crop and environmental factors affecting the survival and colonization of the rhizosphere. Increasing availability of soil P through microbial inoculation will necessitate identification of the most appropriate strains, preparation of effective formulations, and introduction of efficient agronomic managements to ensure delivery and survival of inoculants and associated improvement of P efficiency.