Field-Scale Response to P
Measuring field-scale response to P, K, or both is fairly easy to accomplish using yield monitor data. Yields can be compared from side-by-side strips with and without P/K to see how large the response is, where it is occurring in the field, and to monitor and understand patterns of P and K response on a given landscape or farm.
Soil tests are designed to predict the probability of a yield response to P and K. On-farm measurement tells you much more accurately whether you got a response and how large it was. Soil tests are interpreted based on experiments done under different conditions and on different soils than are likely to exist on your farm.
Yield responses to P may depend on how much P is being supplied by your subsoil.
The University of Missouri is starting a small project to assist producers with this type of on-farm P/K response test. Please email Peter Scharf (firstname.lastname@example.org) if you are interested in participating.
Powerpoint presentation on field-scale P/K response trials
2011 project report