Over-Fertilization Does Not Build Soil Test Phosphorus and Potassium in Ohio

Appropriate P and K fertilizer recommendations for corn (Zea mays L.) and soybean [(Glycine max (L.) Merr.] in Ohio are essential, as water quality and nutrient management issues in the region have intensified over the last several years. The objectives of this study were to: (i) evaluate corn and soybean grain yield response to P and K fertilization, (ii) examine soil test phosphorus (STP) and potassium (STK) and corn Leaf P and Leaf K trends, and (iii) compare the ability of soil and leaf tissue testing to reflect corn and soybean response to fertilization. We evaluated three P and K fertilizer rates, no fertilizer (0x), an estimated nutrient removal rate (1x), and twice the estimated nutrient removal rate (2x), in corn-soybean rotations at three sites over 9 yr. Grain yield was generally non-responsive to P and K fertilization, with only 9 of 42 site-years yielding significantly positive responses. Soil test P and K started in the maintenance range, but significantly declined with the 1x rate at two of three sites for P and at all sites for K. Furthermore, the 2x rate of P and K failed to build STP and STK at any site, with significant declines at one site. The results revealed an inability to maintain initial STP and STK levels with the 1x rate and call into question the suitability of current fertilizer P and K recommendations aimed at maintaining STP and STK. These recommendations require updating to better reflect fertilizer needs of modern corn and soybean.