in the soil was determined by the analysis of mineral nitrogen
(VDLUFA, 2002). For leaves analyses, 25 leaves were collected from
plants of each plot, selecting only fully grown leaves from the
central part of the newborn shoots. Determination of total nitrogen
content of the leaves was carried out by the dry combustion
method (ISO, 2008). For the analysis of potassium, leaves samples
were dissolved in a microwave oven after addition of nitric acid and
hydrogen peroxide; the analytical determinationwas performed by
inductively coupled plasma-optical emission spectroscopy (EPA,
2007).