**4. Environmental concerns**

The productivity of many agroecosystems is largely modulated by plant P-nutrition. Unfortunately, mainly as a result of phosphate extraction, fertilizers application, wastes generation, and P-losses from cropland, humans have perturbed the global P-cycle, which has tripled the global P-mobilization in land–water continuum and also increased P-accumulation in most soils [33]. Owing to the importance of P to life, and the considering the soil to water-sourced P as the major contributor for eutrophication in surface water bodies (and also in natural terrestrial habitats), the maintenance of the P-status of most world soils and its efficient use in agriculture have been focused in recent years. In particular, to attend the prevailing very low availability of Pi for plants/crops, intensive fertilization of crop plants with P-fertilizers (mainly as N-P-K fertilizers globally) is being adopted. Unfortunately, only 10–20% of applied Pi can be absorbed by plants, and rest can remain in the soils as legacy P. Thus, mainly intensive fertilization of crop plants with P-fertilizers has both impeded phosphate rock (non-renewable resource); and has also increased the fertility status of natural waters (eutrophication) due to legacy P (past P surpluses) in soils, sediments, and wastes. Elevated P levels in eutrophic water bodies cause increased growth of algae and large aquatic plants, leading to decreased levels of dissolved O2, and/or algal toxin (produced by algae blooms) and eventual severe impacts on the health of aquatic biota, as well as that of humans and animals. The feeding of the crops with P but not the soils has been suggested in order to properly manage P in the food chain [34]. Thus, unscientific use of fertilizers has eaten away most soil nutrients, disturbed the soil-P balance, inhibited healthy plant growth, and provoked eutrophication and thus has become a major concern in sustainable agriculture production systems worldwide.
