All fertilizer labels have three, prominently displayed, bold numbers. This designation, known as the fertilizer grade, is a national standard. The percentage of each element displayed on the label is guaranteed by a statement of analysis. Blends contain particles of more than one color.
Manufacturers produce various grades, often depending on the target crop.
Single element fertilizer sources are also available for each primary nutrient. Use the same procedure for calculating the amounts of phosphate and potash. The remaining weight is filler, usually sand or granular limestone. The most reliable way to select an appropriate fertilizer grade is to have your soil tested. The soil test report will recommend a fertilizer grade appropriate for the intended crop.