Which ion is primarily used for phosphorus uptake in alkaline soils?

In alkaline soils, phosphorus is primarily taken up by plants in the form of the HPO4^2- ion. This occurs because in alkaline conditions, the pH of the soil increases, which affects the solubility and availability of phosphorus species. As the pH rises, the dihydrogen phosphate ion (H2PO4^-) tends to convert to monohydrogen phosphate (HPO4^2-) as it loses protons.

The HPO4^2- form is stable at higher pH levels and is more available for plant uptake during these conditions. Conversely, the phosphate ion (PO4^3-) is less soluble in alkaline conditions and thus not readily available for absorption by plants. The PO2- ion, which is not a common form of phosphorus found in soils, is generally not involved in the uptake process. Understanding the speciation of phosphorus in relation to soil pH helps in managing soil fertility and improving crop production in various soil types.