P- Fixation Concept

Nature of Phosphate in soil:
P plays important role in plant nutrition is highly reactive element in the soil which is mostly insoluble form in the soil. Phosphate anions are negatively charged in the soil. Plant take two forms of phosphate i.e primary orthophosphate(H2PO4-) and secondary orthophosphate (HPO4-2). Plant take primary orthophosphate (H2PO4-) anions 10 times than secondary orthophosphate (HPO4-2).

P reaction in soil
Every type of Soil naturally contains four types of Cations such as Calcium (Ca),
Magnesium (Mg), Ferrous (Fe) and Aluminum (Al)


When chemical phosphate comes in contact with These Cations (Ca,Mg, Fe And Al) resp. phosphorus get fixed in to the soil and forms Calcium phosphate solid, Manganese phosphate solid, ferrous phosphate solid and Aluminum phosphate solid. Because of this fixed phosphate solid phosphorus become unavailable to plant

Effect of pH on P availability
In alkaline soil P get fixed by excess calcium Cations in the soil.
In acidic soil P get fixed by excess Aluminum Cations in the soil