Effect of Foliar Nitrogen and Magnesium Fertilization on the Total, Protein Nitrogen and Nitrates(V) Content in Potato Tubers

The paper’s aim has been to clarify the effect of foliar fertilization with nitrogen and magnesium on the content of total and protein nitrogen in tubers of medium-early potato cv. Zebra. The experiment was conducted in three series; in the first series, in which potatoes were fertilized only with nitrogen in the total dose of 80 kg N × ha, the contribution of foliar treatment steadily increased (0, 10, 20, 30, 40 and 50 %) at the expense of soil fertilization (80, 72, 64, 48 and 40 kg N × ha); in the other two series included additional magnesium fertilization. In the second series, magnesium at a rate of 7.5 kg Mg × ha was sprayed over potato leaves; in the third series, 15 kg Mg × ha was introduced to soil. The highest average content of total and protein nitrogen was determined in potato tubers which had received exclusive nitrogen fertilization, both as foliar sprays and to soil, whereas in the variants including addition of magnesium, a slight decrease in amounts of both nitrogen forms occurred. The highest increase in the total and protein nitrogen content in potato tubers was obtained at the 10 % contribution of foliar nitrogen application. Magnesium nutrition, either as foliar or soil treatments, did not have any significant influence on the content of total and protein nitrogen in tubers. Increasing share of foliar nitrogen fertilization led to a decreased content of nitrates(V) in potato tubers tested after harvest. A similar effect appeared under the influence of additional foliar application of magnesium, whereas the same nutrient added to soil produced a reverse effect. Magnesium sprayed over leaves tended to lower the concentration of nitrates in potato tubers. When introduced to soil, it raised the content of nitrates(V) in potato tubers.