What is the conversion factor for phosphorus (P) to phosphorous pentoxide (P2O5)?

The conversion factor for phosphorus (P) to phosphorous pentoxide (P2O5) is based on the molecular weights of the two substances. Phosphorus has a molecular weight of approximately 31 g/mol, while phosphorous pentoxide has a molecular weight of about 142 g/mol. To convert phosphorus to phosphorous pentoxide, you use the ratio of their molecular weights.

To perform the conversion, you can use the following calculation:

1 mole of P (31 g) corresponds to 1 mole of P2O5 (142 g). Therefore, the conversion factor is calculated as:

142 g of P2O5 / 31 g of P = 4.58.

However, for practical use in nutrient management where we often deal with balanced nutrient applications, we typically express the amount of phosphorus needed in terms of P2O5 to align with common fertilizer labeling, which results in 2.27 when considering that to get the equivalent amount of phosphorus from P2O5, you divide the molecular weight of P2O5 by that of phosphorus.

Thus, for nutrient management practices, using the value of 2.27 allows for a straightforward conversion when applying fertilizers in forms that contain phosphorus in various ratios and