Influence of Foliar Nitrogen and Magnesium Fertilization on Concentration of Ash Micronutrients in Potato Tubers

Abstract

Abstract: The paper contains a discussion of the results of an experiment concerning the effect of foliar nitrogen and magnesium fertilization on the concentration of ash macronutrients in edible potato tubers of a medium-early cultivar called Zebra. The trials were based on a three-year, two-factorial field experiment, carried out in 2005–2007 at the Research Station in Tomaszkowo, owned by the University of Warmia and Mazury in Olsztyn. The applied fertilization consisted of 80 kgN, 35 kgP and 100 kgK ha. The first experimental factor comprised foliar nitrogen fertilization in the range of doses (8; 40) kgN ha accompanied by simultaneously diminished doses of soil nitrogen fertilization. The second factor included three series: without magnesium, with magnesium introduced to soil in a rate of 24 kg ha and with magnesium sprayed over potato leaves in a rate of 12 kgMg ha. Tuber samples were analyzed for the concentrations of phosphorus, potassium, magnesium and sodium. The content of these macronutrients tended to decrease under the influence of the increasing nitrogen fertilization, with the exception of phosphorus, whose concentration rose in the series unfertilized with magnesium under the effect of 8 and 16 kgN, and the concentration of sodium, which continued to increase in the Mg fertilized series up to the rate of 24 kg of N applied as a foliar fertilizer. The mean Ca : P = 0.28, Ca : Mg = 0.39 and K : Ca = 11.9 ratios suggest very poor calcium supply of the potato cultivar. In contrast, very broad ratios between K : (Ca + Mg) = 3.32 and K : Mg = 4.60 prove that the concentrations of potassium and magnesium were relatively high. The foliar application of nitrogen, tested in this experiment, had a significant effect on the ratios between ash elements in tubers. It has been demonstrated that as the top-dressing rate of nitrogen increased, the Ca : P and Ca : Mg ratios narrowed while the ratios of K : (Ca + Mg) and K : Ca were broader. The applied fertilization had no effect on the K : Mg ratio.