Corn (Zea maysL.) was grown for six consecutive years, beginning in 1966, on Groseclose silt loam to determine the effects of fertilization on leaf composition, yields, and on the changes in available K in the soil. Plant nutrients consisting of five levels each of N, P and K were applied annually in a central composite rotatable design. All plant residue was removed each year when the corn was harvested and the plots were seeded without fertilization to rye as a cover crop.