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Phosphate is a primary component in the chemical fertilizer which is applied in modern agricultural production. Phosphorus, the main component of phosphates, is the second most important nutrient for plant after nitrogen, and for this reason it is often a limiting factor. Phosphorus is especially important in terms of sustainable agriculture since it has the capability to improve soil fertility and crop yields. Phosphorus is involved in all major metabolic processes including photosynthesis, energy transfer, signal transduction, macromolecular biosynthesis, and respiration. It also is involved in root ramification and strength and seed formation and can increase disease resistant capabilities.

Phosphorus can be found in the soil in both inorganic and organic forms and makes up approximately 0.05% of soil biomass. However, only 0.1% of that phosphorus present can be absorbed by plants. This is due to poor solubility and phosphorus’ high reactivity with elements in the soil such as aluminum, calcium, and iron, causing the phosphorus to be fixed. Traditionally, phosphorus has been added to the soil through chemical fertilizers, but the long-term effects of this include eutrophication and soil fertility depletion, so people have looked to other sources.

For phosphorus, an alternative to chemical fertilizers is rock phosphate, which is a valuable natural source of phosphorus already in some soils. In India, there are almost 260 million tons of rock phosphate. However, rock phosphate is a non-renewable resource and because of modern agricultural practices, it is becoming increasingly scarce. However, rock phosphate reserves will be depleted in 50–100 years; peak phosphorus will occur in about 2030. The phenomenon of peak phosphorus is expected to increase food prices as fertilizer costs increase as rock phosphate reserves become more difficult to extract.

A way to make rock phosphate more effective and last longer is to implement microbial inoculants such as phosphate-solubilizing microorganisms, known as PSMs. A source of these PSMs is compost or the recycling of human and animal waste. Specific PSMs have also been isolated and can be added to soil. These PSMs solubilize the phosphorus that is already in the soil and uses processes like organic acid production and ion exchange reactions to make that phosphorus available for plants. When these PSMs are present, there has been an increase in crop growth, particularly in terms of shoot height, dry biomass, and grain yield.

The phosphorus made available by the PSMs can be taken up by the plants on their own, though this uptake is made even more efficient by the presence of mycorrhizae. Mycorrhiza is a type of fungus in the soil that is well-equipped to absorb nutrients, including phosphorus. Nearly all plants have formed symbiotic associations with mycorrhizae. This fungus can increase uptake in soil with limited available phosphorus, such as places with high levels of iron and aluminum where the phosphorus is often fixed. Mycorrhizae can also release certain organic acids that solubilize otherwise unavailable phosphorus.