Verification of Fertilizer Recommendations in a Corn,Wheat,Soybean Rotation in TN.

The University of Tennessee (U.T.) stopped recommending phosphorus and potassium fertilizer additions on soils testing high in P or K in 2009 (Mehlich I extractant).  This was partially in response to the 2008 price increase of these materials. Through funding from the Tennessee department of Agriculture, studies (corn,wheat,soybean rotation) verifying the correctness of U.T. fertilizer recommendations were put in place (spring,2009) at locations in both middle and west TN. At both locations a combination P and K residual study (5 treatments replicated 4 times with both a P and a K control) was placed on a site testing high in both nutrients. Also, a separate P rate study and K rate study respectively (5 rates replicated 5 times) was placed at both locations on sites testing "low to medium" in those nutrients.  Three years were required to crop the High testing sites to medium values for P and K and the "low to medium" sites to low P or K respectively in every replication control plot. Sites testing High in P and K have shown no yield response to date. The now low P and K testing sites began showing somewhat consistent yield response in 2013.