Over‐Fertilization Does Not Build Soil Test Phosphorus and Potassium in Ohio
2018
Fulford, Anthony M. | Culman, Steven W.
CORE IDEAS: Corn and soybean yield seldom responded to P and K fertilization over 9 yr.Soil test P and soil test K significantly decreased from values initially in the recommended maintenance range.Corn Leaf P and Leaf K was often below the sufficiency concentration. 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 (0×), an estimated nutrient removal rate (1×), and twice the estimated nutrient removal rate (2×), 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 1× rate at two of three sites for P and at all sites for K. Furthermore, the 2× 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 1× 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.
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