Soil tests are used to estimate the probability of yield response to P and K fertilizers. Current technology makes it easy to routinely measure yield response to P and K on-farm, doing the same job as soil testing but more accurately. Our objective was to evaluate on-farm response to P and K and to develop ideas for how this information can be used in making management decisions. Strips were left unfertilized during the normal P-K application for several producers. Analysis of yield monitor data showed that response to P and K was not profitable in any of the fields studied, despite low soil test levels. A concept for continued monitoring is developed that will trigger P and K application at removal rates once it becomes profitable.