Grape composition changes during conversion to organic and biodynamic cultivation

This study deals with the changes observed in the first year of conversion to organic and biodynamic cultivation in a vineyard growing Rhine Riesling and Pinot blanc grafted onto SO4 and trained using the simple pergola system in a hilly area in Trentino (Italy). Three farming methods were compared: conventional (CONV; chemical weeding under the rows, grass mowing between rows, mechanical topping and airoperated leaf removal, cluster thinning with gibberellic acid), organic (ORG; soil working under the rows, grass mowing between rows, rolling up the canopy along the furthest wire, air-operated leaf removal and hand fining) and biodynamic (BIOD; soil working under the rows, deep ripping between rows, side-shoot removal by hand, green manure in alternate rows, 2 soil treatments with horn manure 500, 3 leaf treatments with horn silicate 501). The cluster weight, real fertility, yield/vine and Ravaz index were measured. Sugars, total acidity, pH, tartaric and malic acids, K and the assimilable nitrogen of grapes harvested from 10 parcels for each variety at ripeness were measured. In both varieties, BIOD farming showed a higher cluster weight, yield/vine and Ravaz index, while the differences between ORG and CONV were significant in terms of cluster compactness in both varieties and cluster weight and botrytis attack only in the case of Riesling. As regards grape composition, technologically speaking the main differences observed were in pH - slightly lower in the ORG and BIOD plots - and above all in yeast assimilable nitrogen (YAN), while no statistically significant differences were found for °Brix. ORG and BIOD grapes had half the YAN content of the CONV grapes