Rootstock and potassium fertilization, in terms of phenology, thermal demand and chemical evolution, of berries on Niagara Rosada grapevine under subtropical conditions

ABSTRACT

This study aimed to assess the effect of rootstocks (IAC 572 and IAC 766) and potassium fertilization at different concentrations (0, 75, 150 and 300 kg·ha^-1 K₂O) on the phenology and thermal demand of the Niagara Rosada grapevine, and to evaluate the development of chemical traits during maturation stage. The length of the main phenological stages was recorded within two production seasons. Total thermal demand was calculated using the degree-day concept. The berries’ titratable acidity and soluble solids contents were determined during maturation. Results indicated that IAC 572 and IAC 766 rootstocks along with potassium fertilization had no influence on the phenological cycle or thermal demand of the Niagara Rosada grapevine. The production cycle lasted 144 to 148 days with thermal demands ranging from 1,465.2 to 1,615.1 degree-days. For better grape quality, i.e., with a balance between soluble solids and acidity levels, it is estimated that the grape harvest is carried out around 21 to 24 days after the veraison.

Key words
table grapes; grafting; chemical characteristics; degrees-day; potassium fertilization