Soil testing is a key component for determining the need for phosphorus (P) and potassium (K) fertilization. Also, if fertilization is required, test results guide the rate of application recommended to optimize production. Through extensive field research, specific soil tests are calibrated against the expectation of response to applied P and K; that is, they provide both a relative index of the availability of P and K to the crop being grown and an indication of the magnitude of yield increase one might expect when nutrients are applied, thus providing the interpretation of text results.