Corn and Soybean Yields during 11 Years of Phosphorus and Potassium Fertilization on a High-Testing Soil
1991
Mallarino, A. P. | Webb, J. R. | Blackmer, A. M.
Fertilization during the past two decades has increased the number of soils testing high in P and K; this increase has created the need for more information concerning how these soils should be fertilized. A study was conducted from 1979 to 1989 on a high-testing (28 ppm for P, 170 ppm for K) Kenyon loam (fine-loamy, mixed, mesic, Typic Hapludoll) soil in northeastern Iowa to determine the effects of P and K fertilization on soil test values and yields of corn (Zea mays L.) and soybean (Glycine max L. Merr.) grown in rotation. Factorial combinations of 0, 20, and 40 lb P/acre and 0, 60, and 120 lb K/acre were applied annually to each crop. For both nutrients, the greatest rates of application caused increases in soil test values, and the smallest rates caused decreases in these values. Analyses of variance showed that 11-yr means for yields of corn and soybean were not significantly affected by either P or K fertilization. Occasional positive yield responses to fertilization were observed in individual years, but these responses often did not pay fertilizer costs. The results at this site suggest that corn and soybean producers could increase their profits by not applying P or K fertilizers to high-testing soils.
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