The response of Irish potatoes to different amounts and ratios of nitrogen, phosphoric acid and potash when grown in continuous culture

Abstract

In these experiments various amounts of either a 6-12-12 or an 8-12-12 fertilizer were compared as well as a standard amount of different grades having various ratios of N, P and K. Green Mountain and Katahdin varieties were used, yields were determined and data on specific gravity and keeping qualities obtained. The experimental area had been used for growing potatoes for a number of years previous to the beginning of the experiment and was in a high state of fertility. Little response to increasing the application of P2O5 or K2O above the minimum used was obtained. There was a consistent increase in yield resulting from increased nitrogen applications up to about 120–130 pounds per acre. Only relatively small differences in specific gravity of the tubers or in keeping quality was noted as resulting from the different fertilizer treatments. No significant increase in yield resulted from using more than 2000 pounds per acre of a 6-12-12 grade or 1750 pounds of an 8-12-12 per acre. Continuous potato culture with heavy applications of fertilizer results in accumulations of P2O5 and K2O in the soil. The fertilizer grade and amount needs to be adjusted accordingly in order to obtain the most economical return. It is concluded that under these conditions the ratio of N, P and K in the fertilizer should be gradually changed from the customary 1-2-2 to one approaching a 1-1-1 ratio for continuous potato culture. An application of 1500 to 2000 pounds per acre of an 8-12-12, 10-10-10 or similar fertilizer will probably supply all the nutrients needed by the potato crop.