Phosphorus (P) can be extracted from soils with various chemicals. Each extractant removes different amounts of P depending on the soil properties and the strength of the extractant.
How well does the concentration of P in an Olsen bicarbonate extraction correlate to the concentration of total P in soil? How does it compare to the P from a Mehlich 3 extraction? To see what these relationships can look like, I plotted the P concentrations on a 3-dimensional plot below. Click and drag the plot to rotate your view (some extra controls in top left corner). These are some soil samples I collected in the Wasatch Mountains in Utah.
Can you see relationships1? And what do you suppose lends to correlation or lack thereof?
1 Mehlich 3 and Olsen are more correlated with each other than they are to Total.