Influence of factors on phosphorus availability

In natural systems, phosphorus is present in the form of phosphates, which are formed when phosphorus reacts with air oxygen. The availability of phosphorus to plants depends on its condition in the soil.

The state of phosphorus in the soil:

1) Fixed phosphorus:

• The largest pool of phosphorus in the soil that is not available to plants.
• It dissolves very slowly.
• It consists of insoluble inorganic phosphate compounds (primary minerals) and organic phosphorus compounds.

2) Active phosphorus:

• It is easily released and is the main source of phosphorus for plants.
• It is composed of inorganic phosphate adsorbed to soil particles, secondary phosphate minerals (phosphate bound to cations such as calcium and aluminum) and organic phosphorus, which is easily mineralized.

3) Dissolved phosphorus:

• The smallest pool available for plant uptake.
• Consists mainly of inorganic phosphates, with a small amount of organic phosphorus.
• It is quickly depleted and constantly replenished from the active pool.

Factors affecting phosphorus availability:

1) soil pH:

• The optimal pH range for phosphorus availability is 6.0 to 7.0.
• A low pH binds phosphate to aluminum or iron, while a higher pH binds it to calcium.

2) Soil type:

• Heavily weathered soils have a high sorption capacity, which reduces the availability of phosphorus.
• Less weathered and organic soils have a lower sorption capacity.

3) Clay content:

• Increases sorption capacity due to the large surface of clay particles.

4) Organic matter:

• Higher levels of organic matter usually lead to greater phosphorus availability for crops.

5) Other anions:

• Anions such as bicarbonate, carbonate, silicate, sulfate or molybdate compete for sorption sites, reducing phosphate adsorption.

6) Climate and soil conditions:

• Soil temperature, moisture, aeration and salinity affect the rate of phosphorus mineralization.

Phosphorus loss is often associated with erosion and leaching. Phosphate bound to soil particles is carried away with eroded sediment.

Recommendations:

• Control the pH of the soil
• Analyze the soil type
• Maintain a high organic matter content
• Avoid erosion and leaching

All of this will help improve phosphorus availability!