A LONG-TERM FIELD EXPERIMENT WITH COMMERCIAL FERTILIZERS AND MANURE.: II. FERTILITY LEVELS AND CROP YIELDS IN A ROTATION OF POTATOES, OATS AND HAY

Treatments in a field experiment, conducted from 1936 to 1957, included commercial fertilizers and manure. A rotation of potatoes, oats and hay was followed.Application of manure at 30 tons per acre every third year practically maintained initial levels of total nitrogen and soil organic matter. Marked decreases occurred with lower rates of manure and various commercial fertilizers applied at 1 ton per acre. Increases and decreases in adsorbed and easily acid-soluble phosphorus were directly related to the amounts of phosphatic fertilizer applied. Although the situation with respect to exchangeable potassium was not comparable there was some evidence that final values were influenced by the amounts of potassium applied.All treatments were applied for potatoes, and yield differences were much greater for this crop than for either oats or hay. Rate of fertilizer application was of primary importance for potatoes, and residual effects on the oat and hay crops from 500 or 1000 pounds of commercial fertilizer per acre were generally slight. They were much more marked from manure and where commercial fertilizer was applied at a ton per acre. Irrespective of the treatment applied, linear regression coefficients, showing yield trends with advancing rotation cycles, were positive for potatoes and negative for hay. In the case of oats they were generally negative for the lowest rates of fertilizer used and positive for the highest.