I. Forms and Availability of Phosphorus in Soil Soil phosphorus can be categorized into two major classes based on its chemical properties:  organic phosphorus  and  inorganic phosphorus . The vast majority exists in forms not readily available to plants, such as insoluble inorganic phosphates bound to iron, aluminum, and calcium, or as organic phosphorus compounds (e.g., phytates, phospholipids). Plants primarily absorb  orthophosphate ions (H₂PO₄⁻ or HPO₄²⁻)  from the soil

Ammonium Polyphosphate (APP) , CAS No. 68333-79-9 , is a high-performance, low-nitrogen, high-phosphorus polymeric phosphate compound...