**1. Introduction**

Plants (crops), soils, and humans are intricately interrelated. As heterotrophs, humans (and animals) largely depend on plants and/or on the plant-associated food resources. Seventeen (17) nutrient elements are varyingly required by plants in optimum level for the maintenance of their growth, metabolism, and productivity, as well as for their sustenance under adverse conditions. These elements are also called nutrients and include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn). Interestingly, N, P, K, S, Ca, Mg, B, Cl, Cu, Fe, Mn, Mo, Ni, and Zn are derived from the soil (or parent rock materials) and can also be supplied by fertilizers. On the other hand, the list of non-minerals includes C, H, and O since these elements are obtained from water, air, or both. In addition to nourishing the plants, soils also provide anchorage, air (O2), water, temperature modification, and the stabilization. As an essential plant macronutrient, P has been a key regulatory element for plant growth and metabolism. Unfortunately, P-bioavailability has been a worldwide constraint for plant growth and productivity. There must be a fine P-homeostasis in the soil-plant system in order to maintain the status of the soil-P and its efficient uptake and metabolism in plants, for optimum plant growth and productivity and eventually for attaining agricultural and environmental sustainability and the global food security.
