Abstract

Potassium (K) is generally considered as a nutrient which significantly affects nitrogen use efficiency (NUE). This relationship was tested in a field experiment with rain-fed potatoes cultivated on a light soil. The experiment consisted of four K doses: 0, 80, 160, or 240 kg K₂O ha^-1 and two N doses: 120 or 160 kg N ha^-1. The effect of residual K was tested against the background of 90 kg K₂O ha^-1 applied to winter wheat sown consecutively. Potato yields responded positively to increasing K dose, especially in 2013, a year characterized by mild water stress in the summer months. A positive impact of K application on tuber yields was obtained in relation to the increased N dose. The harvested tuber yield showed a linear response to increasing N uptake but curvilinear to increasing K uptake, with an optimum at 170 kg K ha^-1. Thus, potato fertilized with 160 K₂O ha^-1 and with 160 kg N ha^-1 reached highest productivity. However, the most efficient use of applied nutrients, as demonstrated by analyses of the agronomic index of NUE, was a fertilizer combination of 160 K₂O ha^-1 and 120 kg N ha^-1. Elevated amounts of K fertilizer resulted in some increase of the soil K available pool. This pool in 2013, following the 2012 potato crop, was high enough to significantly increase the productivity of the consecutive winter wheat, but a similar effect did not occur in the winter of 2014.