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Fig. 1. Map of the Morrow Plots. U, unamended; U-NPK, unamended until 1955, currently fertilized for corn with 224 kg N ha–1, Bray-1 P = 56 kg ha–1, and exchangeable K = 336 kg ha–1; H-NPK, treated with manure, limestone, and rock phosphate from 1904–1966 and subsequently fertilized for corn with 336 kg N ha–1, Bray-1 P = 112 kg ha–1, and exchangeable K = 560 kg ha–1; M-NPK, treated with manure, limestone, and rock phosphate from 1904–1954 and since fertilized as with the U-NPK treatment; M, manured. The subplots studied are shaded.
