Abstract
The interaction of mechanized pruning systems and soil organic amendment can affect vine vegetative and reproductive growth. However, since organic amendments supply several mineral elements, namely heavy metals, this study aimed to understand the effects of the interaction between these two practices on the mineral composition of wine. Two field trials were implemented in ‘Syrah’ vineyards in two Portuguese wine regions (Lisboa and Tejo). Mechanical hedge pruning was compared with hand spur pruning and four different organic amendments were tested: biochar, municipal solid waste compost, cattle manure and sewage sludge. The nitrogen (N), phosphorus (P) and potassium (K) wine contents were significantly reduced by mechanical pruning while calcium (Ca) and magnesium (Mg) contents were tendentially higher in this pruning system. Mechanical pruning also reduced the content of some minor elements, such as arsenic (As), molybdenum (Mo) and nickel (Ni). In 2014, the year with the higher reproductive growth, some other elements also decreased as a consequence of the mechanical pruning (gallium - Ga; lithium – Li; rubidium - Rb, thallium – Tl; yttrium - Y). Concerning the organic amendments, sewage sludge was associated with the wines with the lowest P and iron (Fe) content. Ca content was tendentially higher in municipal solid waste compost and sewage sludge treatments. Mechanical pruning and organic amendments had different effects on the mineral composition of wine, according to each specific element. However, the legal limits, recommended by OIV and established by European Union, as well as the technical limits, adopted by winemakers, were never exceeded and the interaction of both practices does not seem to be a problem in what concerns to the mineral composition of the produced wines.
Highlights
The mineral content of wines depends on several aspects, including environmental conditions, soil, grape variety, and viticultural and enological practices
The results presented in this work correspond only to the last three years of the research project, since, in 2012, no significant effects were observed in wine mineral composition
Since some viticultural data are important to understand the effects of the studied factors on mineral composition of wines, some of the data already reported in Botelho et al (2020), are presented: Mechanical pruning induced a significant increase in bud load (MAN – 13.9 buds/vine; mechanical pruning (MEC) – 54.9 buds/vine) and in the shoot number per vine (MAN – 20.4 shoots/vine; MEC – 32.6 shoots/vine) and in yield (MAN – 4.74/kg/vine; MEC – 6.23/kg/vine)
Summary
The mineral content of wines depends on several aspects, including environmental conditions, soil, grape variety, and viticultural and enological practices. Some elements must be determined due to their toxicological and physiological properties and some others can lead to wine spoilage (Catarino et al, 2006, 2008a). There are other factors that can affect wine mineral content, namely soil amendments and fertilizers, irrigation water, atmospheric pollution, pesticides, contact with materials during transport, vinification and ageing processes, and enological processing aids and additives (Catarino et al, 2008b; Volpe et al, 2009). The precipitation of K and Ca as tartrate salts starts during alcoholic fermentation and remains during the ageing period. Heavy metals precipitate as insoluble salts, namely as sulfides, a phenomenon that is favored by the addition of sulfur dioxide during winemaking (Ribéreau-Gayon et al, 2000)
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