Hi, I get confused when gardeners from the US talk about Nitrogen, Phosphorus and Potassium levels in Fertilizers. I live in Australia and our system must be different. For example a good lawn fertiliser would be N 27 PH 1.3 POT 3.3. Is there a way to convert? regards Wolfgang
here the numbers refer to actual percentage of the package weight of the supposed element. so if we have 20-20-20, that means that 20% of the weight of the package ingredients is nitrogen, 20% is phosphorous, 20% is potassium. leaving 40% of the weight for the carrier, clay etc.
NPK actually refers to N, P2O5, and K2O. In other words, 10-10-10 actually means you're guaranteed 10% nitrogen, 4.4% phosphorus, and 8.3% potassium (by weight), because 44% of P2O5 is P and 83% of K2O is K. (Why doesn't NPK just stand for NPK? Beats me.) I don't know the Australian convention, but if NPK is NPK down under, then converting is simply a matter of using the 4.4 and 8.3 percent figures. Obviously, the distinction is important if the soil is P or K-deficient or when nutrient balance is a problem. Also, I consider a 'good fertilizer' to be one that meets your lawn's needs without 'overdoing it,' one that is cost-effective and environmentally sensitive, not necessarily one with a certain NPK.
