Soil-Testing

An Important Step In Feeding Your Lawn Correctly

Soil-testing  is necessary to establish the proper lawn fertility program for a specific site. Soil tests can be obtained by submitting a soil sample to private soil fertility testing laboratories or to the University of Minnesota Soil-Testing Laboratory. Informational sheets and materials can be obtained through your county extension office or online at University Of Minnesota (use the link below).

The proper ratio of nitrogen, phosphorus, and potassium to apply to a lawn can only be determined by soil testing. Since nitrogen can move out of the root zone with percolating water or as a gas, soil tests for available nitrogen are not very meaningful and are generally not performed. Phosphorus and potassium move little in the soil and consequently soil tests will be valid for several years. The most important soil test is the first one so that you can establish the base levels of P and K in the soil. Subsequent sampling may not be necessary for many years if phosphorus and potassium levels are adequate.

The label on lawn fertilizer bags lists the percentages of the three primary nutrients as a series of three numbers called the fertilizer grade. As an example, a common lawn fertilizer grade is 23-0-6. In this case the fertilizer contains 23% nitrogen, phosphorus equivalent to 0% P₂0₅, and potassium equivalent to 6% K₂O.

One fertilizer grade is not best for all soils, since native soil phosphorus and potassium levels as well as previous fertilizer practices determine needs. If a soil is already high in phosphorus and potassium, a fertilizer with a grade of 21-0-0 or 46-0-0 would be sufficient, while a soil with low phosphorus or potassium would require additions of fertilizer containing phosphorus or potassium such as 20-5-10 or 23-0-6.