Historically, soil testing has been used to quantify availability of essential plant nutrients to field-grown crops. However, contemporary soil tests are based on philosophies and procedures developed several decades ago, without significant changes in their general approach. For a soil test to be accurate, one needs to clearly understand the physico-chemico-physiological processes at the soil-root interface and, an understanding of soils and plant root systems as polycationic systems is essential. It is this knowledge that leads to sound prescriptive soil nutrient management inasmuch as soil nutrient bioavailability vis-à-vis fertilizer application is concerned, because, of all the factors which govern sustainability in crop production, the nutrient factor is the most important, yet, it is also least resilient to management. This book focusses on the thermodynamics of soil nutrient bioavailability, especially, of most important plant nutrients, phosphorus and potassium, among major nutrients, and zinc among micronutrients. It proposes a paradigm shift in the approach to global soil testing procedures