Rate of Phosphorus and Potassium Buildup/Decline with Fertilization for Corn and Wheat on Nebraska Mollisols

Abstract A 12‐yr study was conducted on four Mollisols in Nebraska to evaluate response of corn ( Zea mays L.) and wheat ( Triticum aestivum L.) to P and K fertilizers and to determine the rate of buildup or decline of these nutrients in soil. Rates of P were 0, 11, 22, and 33 kg ha −1 applied annually or in less frequent applications of higher rates in order to maintain the same average seasonal amount, along with 27 and 54 kg annual K rates ha −1 in association with 22 kg P. The P and K fertilizers were broadcast and incorporated before planting with an appropriate blanket N treatment for the two crops. Positive yield response to applied P resulted when soil test P by Bray and Kurtz no. 1 procedure was below 15 mg kg −1 for corn and 22 mg kg −1 for wheat. No positive yield response to applied K was measured in these soils of high exchangeable K but rather a yield depression was observed at the high K rate. No significant differences in yield existed between annual applications of P and the heavier less frequent applications. Soil test P level was maintained by annual P rates of 4 to 13 kg ha −1 on the eastern soils, with none applied in the west, and was more than doubled on all soils at the end of the experimental period with 33 kg applied. Three of the soils evidenced distinct increases in soil test K without K application; the fourth a slight decline. Results from P fractionations of the test soils are reported to aid in interpreting the yield results.