Investigating how soil pH and other soil properties affect the wine grape quality

Abstract

Following the Phylloxera epidemic in the twentieth century, Vitis vinifera grapevines were grafted onto various types of rootstocks as defence mechanisms. Since then, with the protection provided by the rootstock and other factors, the quality of Maltese wine has come a long way, ever improving. Nineteen vineyards around the Maltese islands were investigated for properties pertaining to the pedology and wine grape features. Soil parameters explored were pH, electrical conductivity (EC(1:5)), nitrate concentration, and texture. Additionally, wine grape parameters investigated were those of pH, titratable acidity, tonality ratio, colour intensity, and anthocyanin content. All parameters were cross-referenced against each other using a linear regression test, Spearman's rank correlation and principal component analysis (PCA). Although foreign studies suggested otherwise, there is no significant relationship between soil pH and grape quality on a local scale. However, there is a positive correlation between nitrate concentrations and grape acidity. Furthermore, the grape parameters indicate a positive or negative relationship to one another. Since the close relationship was discovered between local pedology and wine grape results pertaining to nitrate concentrations and acidity, recommendations for further studies were highly influenced by this result. This study encountered several challenges, which unfortunately, potentially compromised the results. Regardless, the results are conclusive and indicate no relationship between the pedological and Vitis vinifera parameters, other than that linking nitrogen levels and titratable acidity - two extremely important factors for satisfactory vinification results.