**3. Why we worry of phosphorus use efficiency**

Phosphorus use efficiency has become burning issues in recent times due to several reasons [24]. Unlike N, the amount of P is less-abundant, finite resource, less-available, and poor mobility in the soil, being one of the most inaccessible elements for plants. Its deficiency is a major constraint to agricultural production, and it affects an area of over 2 billion hectares worldwide that is on about 70% of the world's arable land [25]. Remarkably, usually only about 10–30% of the P fertilizer applied in the first year is taken up by the roots, with a substantial part accumulated in the soil as residual P not readily available for plants [26]. This may be due to nature of P that can bound to calcium in alkaline soils and readily complexed to charged Al and Fe oxides and groups hydroxyls on clay surfaces in acidic soils [23]. In addition, agricultural phosphorus (P) run-off is a primary factor in the eutrophication of aquatic and marine ecosystems and has also led to blooms of toxic cyanobacteria [27] and can contain heavy metals such as cadmium that may accumulate in arable soils. Moreover, organic material present in the soil (e.g., from manure or crop residues) can also bind phosphate ions as well as phytate (inositol compounds). In order to avoid a future food-related crisis, phosphorus scarcity needs to be recognized and addressed in contemporary discussions on global environmental change and food security, alongside water, energy, and nitrogen [28].
