Certified Crop Advisor Practice Exam

What is the chemical uptake form of phosphorus?

1. PO4^3-

2. H2PO4-

3. P2O5

4. PO3^2-

The correct answer is: H2PO4-

The chemical uptake form of phosphorus in plants is H2PO4-. This form is known as dihydrogen phosphate, which plays a crucial role in plant metabolism and is readily absorbed by plant roots. Phosphorus in the soil can exist in various forms, but H2PO4- is the most bioavailable for plant uptake, particularly in slightly acidic to neutral pH conditions (around pH 6 to 7). In this form, phosphorus is involved in essential processes such as energy transfer (as part of ATP), photosynthesis, and the synthesis of nucleic acids. While phosphorus can also exist in other chemical forms, such as PO4^3- (phosphate) and P2O5 (which is a representation of the phosphorus pentoxide that describes phosphorus in fertilizers), these forms are not the primary means by which plants take up phosphorus. The PO3^2- form is less common in soil and does not typically contribute significantly to plant nutrition. Thus, H2PO4- is the optimal and most relevant form for plant absorption from the soil.