The nitrogen (N) critical level in leaves and maximum technical efficiency (MTE) doses contribute to the grape yield, must quality, and fertilizers rationalization. This study aimed to define sufficient ranges and critical levels in leaves and maximum technical efficiency doses to obtain high yields and quality must in grapevines grown in sandy soil in a subtropical climate. ‘Chardonnay’ and ‘Pinot Noir’ grapevines were subjected to the annual application of 0, 10, 20, 40, 60, and 80 kg N ha−1 in a vineyard. The nitrogen concentration in leaves at flowering and veraison, grape yield and grape must chemical parameters (total soluble solids—TSS, total titratable acidity—TTA and total anthocyanins—TA) were evaluated. The N critical level in leaves at flowering was different between grapevines cultivars, but this was not observed in leaves at veraison. It was possible to estimate MTE for ‘Chardonnay’ grapevines, in the evaluated growing seasons. In the range of higher probability of the N critical level in leaves, the TSS and TTA variables showed opposite responses, for both cultivars. This study proposes different N critical levels for red and white grapevines, in a subtropical climate.