Much of the phosphorus (P) fertilizer applied across the US is applied using a variable rate (VR) strategy. Often we interpolate soil P data and use standard soil test interpretations to develop VR prescriptions. We need to critically examine this approach. Can traditional soil test critical values (the soil P concentration below which we expect P fertilizer response) and fertilizer recommendation systems be used under a VR management strategy? How precise are interpolated soil test maps? These questions and others will be examined as we discuss ongoing research into VR-P.

Potassium, as a non-mobile nutrient, is commonly thought to stay put in soils; however, this should not imply that soil test K levels are constant throughout the year. Seasonal variability in soil test K from spring to fall (often higher in spring and lower in fall) creates issues for soil sampling and interpreting soil test results for fertilizer applications. This session will cover soil K dynamics and approaches to mitigate seasonal K variability to improve nutrient management decisions.

Leveraging spatial analytics to calibrate fertilizer recommendations improves the efficiency of applied fertilizers. In many cases, fertilizer recommendations have not been recently updated, in part due to a lack of funding and man-power. Today's technology and the analytical capabilities allow for the optimization of field specific fertilizer recommendations that fit grower management styles and soils.