A LONG-TERM FIELD EXPERIMENT WITH COMMERCIAL FERTILIZERS AND MANURE: III. FERTILITY LEVELS, CROP YIELDS, AND NUTRIENT LEVELS IN CORN, OATS, AND CLOVER

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Abstract
Changes in adsorbed plus easily acid-soluble phosphorus in soil were generally proportional to the amounts of phosphorus applied.All treatments were applied in the corn year and the phosphorus content of fertilizers was reflected in the per cent total phosphorus in tissue samples of corn and the succeeding oat and clover crops. Application of fertilizers containing increasing percentages of potassium consistently increased the per cent total potassium in com and oats but not in clover. However application rates of manure were invariably reflected in the percentages of total phosphorus and potassium in all crops. With 20 tons of manure corn, oats, and clover contained 0.33, 0.28, and 0.27% phosphorus and 2.51, 1.92, and 1.42% potassium.Application of fertilizers with increasing percentages of nitrogen did not produce significant yield differences in any of the crops. However, use of fertilizers containing increasing percentages of phosphorus or potassium resulted in significantly increased corn yields. All crop yields were significantly higher with 20 tons of manure than with 1000 lb of 4-8-8 fertilizer. With this rate of manure corn produced 3.18 tons of dry matter, oats approximately 52 bu, and hay 2 tons of dry matter per acre.
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