In alkaline soils, what forms insoluble phosphorus?

In alkaline soils, calcium precipitates are the primary factor that leads to the formation of insoluble phosphorus. This occurs due to the high pH levels typically associated with alkaline soils, where calcium (Ca) can combine with phosphate ions to form calcium phosphate compounds. These compounds, such as hydroxyapatite, have low solubility in alkaline conditions, which significantly reduces the availability of phosphorus for plant uptake.

The precipitation of calcium phosphate is crucial for understanding nutrient availability in alkaline soils, as it can limit the effective use of fertilizers that contain phosphorus, ultimately impacting plant growth and crop yields. Therefore, the formation of these insoluble compounds is a critical concern for nutrient management practices in agriculture, especially in regions with alkaline soil conditions.