Nitrogen and potassium fertilization of potato

Fourteen one-year N- and K-fertilization experiments for potato were carried out on coarse mineral soils on different sites in Finland. The nitrogen fertilization (from 50 to 156 kg/ha N) was given in the form of ammonium nitrate limestone, and the potassium (42—179 kg/ha K) in potassium sulphate. The nitrogen fertilization affected significantly both the yield and the quality of the tubers. The maximum tuber yield was achieved at the nitrogen application rate of 110 kg/ha. The economically most advantageous fertilization rate was 80 kg of nitrogen per hectare, if only the amount of the yield was taken into account. The nitrogen fertilization weakened the quality of the tubers. The weight and the size of the tubers increased, but the starch content of the tubers decreased as a result of the nitrogen fertilization. The starch yield also turned out to be the smallest at the heaviest nitrogen fertilization. Further, the biggest rate of nitrogen weakened the flavor of the tubers, depressed their mealiness, and increased slightly their discoloration when raw. The fertilization had no effect on the darkening of cooked potatoes. In these one-year experiments, the increase of the potassium fertilization from 42 kg/ha K did not have a significant effect on the yield and the quality of the tubers.