Quantity and quality of potato yield as influenced by unbalanced and excessive fertilization

Potato (var. Rekord) was cultivated for three years in a sandy field. It was given various levels of three fertilizers the N, P and K composition of which in percentages was 7-11-12, 18-3-12 and 27.5-0-0. The N levels were 0, 80/60, 140/120 and 300/240 kg/ha (1983/1984-85), but the P and K levels varied according to the composition of the fertilizers. In the first year the yields were high regardless of fertilization. The following years the yields were clearly highest in the plots where the fertilizer 7-11-12 was used. This was due to insufficient P and K supply in the other plots. With increasing N fertilization the starch content and mealiness of the tubers decreased and the flavor was degraded. The two higher N levels yielded a considerably higher nitrate content than was measured in tubers from unfertilized plots and those receiving the lowest levels of fertilizers. The present results point out the significance of appropriate N fertilization for potato. A certain N amount was necessary to produce a quantitatively satisfactory yield but excessive amounts had an adverse effect on the quality. P and K were of minor importance for the quality in this experiment, but abundant P and K fertilization was needed for optimum yield formation. Maintenance of soil K level proved difficult in continuous potato cultivation