Conversion factors: plants and their nutrients

In practice, it looks like this: Gardener A from Germany has problems with his plants and asks the community for advice. Gardener B from Canada wants to help and asks Gardener A for more information and then uses the analysis of the nutrient solution (from Gardener A) as a guide. Gardener A mentions a P value of 100 ppm, but calculates with the phosphorus pentoxide (P₂O₅). Gardener B, however, assumes that the P value is P in its elementary form and advises Gardener A to at least halve the P value. If gardener A were to implement this without questioning, he would probably have further problems (P deficiency), since the conversion factor from P to P₂O₅ is 2.2914. In other words, the P value of 100 ppm (P₂O₅) of gardener A corresponds to a P value of gardener B of 43.64 ppm (P).

In order to avoid problems of this kind, one should always pay close attention to the form of the respective nutrient. If in doubt, it is always worth checking again before making any adjustments to the nutrient solution.

Here is an overview of the most important conversion factors:

Calcium
Calcium (Ca) zu Calciumoxide (CaO): 1,399
Calcium Oxide (CaO) and Calcium (Ca): 0.7147

Magnesium
Magnesium (Mg) to Magnesium Oxide (MgO): 1.658
Magnesium Oxide (MgO) to Magnesium (Mg): 0.6032

Phosphorus
Phosphorus (P) to phosphorus pentoxide (P₂O₅): 2,2914
Phosphorpentoxid (P₂O₅) to phosphorus (P): 0.4364

Potassium
Potassium (K) to Potassium Oxide (K₂O): 1.205
Potassium oxide (K₂O) to potassium (K): 0.8302

Sulfur
Sulfur (S) to sulfur dioxide (SO₂): 1,998
Sulfur dioxide (SO₂) to sulfur (S): 0.501

Sulfur (S) to sulfur trioxide (SO₃): 2,497
Sulfur trioxide (SO₃) to sulfur (S): 0.4

Sulfur (S) to sulfate (SO₄): 2,996
Sulfat (SO₄) to sulfur (S): 0.334

Nitrogen

Nitrogen (N) to nitrate (NO₃): 4,427
Nitrate (NO₃) to nitrogen (N): 0.226

Nitrogen (N) to ammonium (NH₄): 1,288
Ammonium (NH₄) to nitrogen (N): 0.777