Productivity and quality of grapes of CV. Isabel submetidas a adubacao potassica

Grapevine 'Isabel' grafted on rootstock 'SO4' and 'IAC 766' and planted on ungrafted Nitosol were treated annually with increasing concentrations of [K.sub.2]O, 0; 60; 120 and 180 kg [ha.sup.-1] for 5 wine-growing seasons (2007/08,2008/09,2009/10,2010/11 and 2011/12). The experimental design was banded with five replications, with six plants per replication and the treatments in a 4x3 factorial design, with 12 treatments, corresponding to four doses of potassium fertilization and the three rootstocks. The stage of berries peel color change, stems were collected to determine the nutrient content in the grape leaves. At the time of harvest it was evaluated vegetative and productive behavior, such as productivity, weight pruning, Ravaz index, and analytical characteristics of berries, total soluble solids, titratable acidity and pH were evaluated. Increased potassium fertilization does not represent a gain in productivity in cv. Isabel nor the accumulation of soluble solids in grapes. K and Mg in petioles of grapes are influenced by the form of cultivation (grafted or ungrafted). 'Isabel' vines grown on ungrafted have less capacity to accumulation of K and higher of Mg in the petioles. Under the conditions of the soil that was developed the research is not justified potassium fertilization of the vineyard.