DBFarms17 - 3/24/2017 12:27 Please be careful with advice on here... Again, another factor is needed when converting pounds per acre of phosphorus and potassium in their oxide forms into number of ppm in their elemental forms: 0.4364 and 0.8302, respectively. Why? Please explain how converting to elemental forms is important in regards to a soil test, since the labs themselves do not even do it? Or at least I don't know of any..... For example, to convert 100 pounds per acre of phosphate fertilizer (P2O5) to ppm of elemental phosphorus, just multiply 100 by 0.5 and then by 0.4364 to get 21.8 ppm of phosphorus. Similarly, 100 pounds per acre of potash fertilizer (K2O) will increase soil potassium (K) by 41.5 ppm. The conversion equations are below. More conversions are available in Table 2. Pounds of nutrient applied per acre × 0.5 = increment of the nutrient in soil (ppm) Pounds of phosphorus pentoxide applied per acre × 0.5 × 0.4364 = increment of phosphorus in soil (ppm) Pounds of potassium oxide applied per acre × 0.5× 0.8302 = increment of potassium in soil (ppm) I think you are taking an inexact science and adding a lot of unneeded complexity. The soil is a living, moving entity. As such, the soil test is just a snapshot in time....similar to a tissue sample. And the tests themselves are not 100% reliable (see pic). This is why "ranges" are used in trying to make recommendations I believe. We want to have adequate availability of nutrients, but it is not as simple as adding "X" lbs of potash will get us "Y" on the soil test potassium. If anything, I have learned that nothing in the soil is absolute.
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Fertilizer Advice
