**3. Forms of phosphorus in soil**

The total P in soil is a combination of both inorganic and organic forms. Generally, the inorganic P is higher than the organic P because it accounts for around 50–85% of soil total P [42]. The inorganic P constitutes some active forms of P like calcium P (Ca-P), iron P (Fe-P), and aluminum P (Al-P) and inactive forms like occluded P, reductant soluble P, and residual P [43, 44]. The concentration of total P ranges from 50 to 3000 ppm in soils, but it has little contribution to the bioavailability of P in soils [45]. The solution P, which meets the plant's requirement, is available in very low concentrations (around 0.05 ppm) in soil [46].

Organic P consists of inositol phosphates, phospholipids, and nucleic acids. Inositol phosphates exist as a dominant pool of organic P in soil because the other two forms are highly susceptible to microbial degradation [47]. Globally, the share of organic P in total soil P is observed between 1 and 30% [48, 49]. In Indian soils, this share varied from 10 to 50% [50]. However, the contribution of organic P may increase up to 80% in forest and grassland ecosystems [51].
