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Utilization of Residual Fertility by Potatoes¹

ABSTRACT

Inherently the soils of Maine do not possess a high natural fertility. Analyses of virgin samples show that such soils contain about 5% of organic matter, 44 pounds of readily soluble P₂O₅ per acre, and 76 pounds of exchangeable K₂O per acre and have pH readings ranging from 4.5 to 5.0. As a result of intensive fertilization over a period of years the amount of P₂O₅ per acre has increased to about 100 pounds per acre, and the amount of K₂O has increased to about 200 pounds per acre.

The Katahdin variety of potatoes was grown. The fertilizer applications were 2,000 pounds of each of the following fertilizers: 6-0-0, 6-9-0, 6-0-9, and 6-9-9. The fertilizer was applied each time the plot was in potatoes. The yield results showed that dropping phosphorus out of the fertilizer significantly decreased the yields in all cases. In 1951 the climination of potassium did not significantly reduce the yield. In 1952 the elimination of potassium did cause a significant decrease in yield. It would appear that potatoes can mine the potassium reserves in the soil more efficiently than the phosphorus reserves.

¹ Contribution from the Agronomy Department, Maine Agricultural Experiment Station, Orono, Me.

² Agronomist and Assistant Agronomists, respectively.

Received for publication July 15, 1954.