Concept of Lime Potential comes from which law?

The concept of Lime potential comes from Schofield's Ratio Law. As per the law, the lime potential is a measure of the sum of the activities of calcium and magnesium hydroxides in the solution and is, therefore, a measure of the base status of the soil solution.
The lime potential is a simple function of the chemical potential of calcium hydroxide, lime. The mathematical expression of lime potential is pH - 0.5 pCa.