Using foliar applications of magnesium and potassium to improve yields and some qualitative parameters of vine grapes (Vitis vinifera L.)

In a three-year field experiment (2011-2013) we assessed the effect of magnesium (MgSO4) and potassium (K2SO4) applied as foliar applications both separately (3.86 kg Mg/ha or 12.44 kg K/ha) and in combination (1.93 kg Mg/ha + 6.22 kg K/ha) on yields of grapes of cv. Zweigelt and some qualitative parameters of the grapes. The applications were repeated 4 times in stages BBCH 15-19; 55; 75 and 83. The experiment was carried out on soil well supplied with Mg and K in the subsoil layer. In terms of average 3-year results the grape yields were by 11.2% (MgSO4), 13.9% (K2SO4) and 6.6% (MgSO4 + K2SO4) significantly higher than the untreated control. The sugar content of grapes (sum of glucose and fructose) was lower (mostly insignificantly) by 0.5-4.3% in all the fertilized treatments than in the untreated control. Fertilization had no significant impact on the pH of must (juice) and ranged between 3.02 and 3.25. The content of titratable acids in the must ranged insignificantly between 8.73 and 10.86 g/L, and average values were the highest in the untreated control. On the basis of these results it is evident that separate applications of Mg and K have a positive effect, in particular in that they stimulate grape yields, and at the same time the effect of the year is significant.