Corn and Soybean Yield Response to Phosphorus and Potassium Fertilization in Ohio.

In Ohio, phosphorus (P) and potassium (K) recommendations for corn and soybean were last updated in 1995 with the Tri-State Fertilizer Recommendations. Water quality and nutrient management issues in the state have stimulated interest in re-evaluating these recommendations after more than 2 decades. Therefore, the objectives of this study were to i) determine soil test P and K critical levels that indicate likelihood of crop response to P and K fertilization, ii) determine sufficiency ranges for early reproductive (R1) tissue of non-responsive corn and soybean. From 2014-2016 we conducted over 90 on-farm trials in P in corn and soybean and over 75 trials in K for corn and soybean in Ohio. All trials were replicated and randomized and employed both large strip trials and small plot trials formats. Soil test P and K, leaf tissue concentrations at R1, grain nutrient concentrations at harvest and grain yields were measured on all trials. Soil tests values ranged greatly, with soil test phosphorus values from 8 – 377 mg P kg^-1 soil, and soil test potassium values from 55 - 563 mg K kg^-1 soil (Mehlich-3). Overall, grain yield responses to P or K fertilization were rarely observed with <5% of trials for both P and K demonstrating statistically significant responses. Overall, our results suggest that current fertilizer recommendations in Ohio are not too low and that current critical levels for soil test P and K provide a very conservative range for corn and soybean.