The extractant used for available phosphorus in soils is

The extractant used for available phosphorus in soils is 0.5 M NaHCO₃, (Olsen). It is the most widely used method in P extraction for Routine fertility purposes, although it was initially proposed for neutral and alkaline soils.
An extractant is a liquid used to remove a solute from a solution. Here, in Olsen method uses NaHCO₃ extractant that can remove Ca-Phosphates and phosphate absorbed on the surface of surfaces of calcium and magnesium carbonates along with Al-phosphates. Phosphorus is extracted from the soil with 0.5 M NaHCO₃ at a nearly constant pH of 8.5.