Conversion to organic and biodynamic viticultural practices: impact on soil, grapevine development and grape quality

Aim: The effects of integrated, organic and biodynamic management on soil quality and the growth and morphological development of Riesling grapevines were assessed during the first 4 years of a long-term field trial in Geisenheim, Germany. The overall aim was to understand the effects of these different viticultural practices on soil quality and plant morphology as the basis for product quality. Methods and results: As indicators of soil quality, earthworm abundance and the activity of selected enzymes were assessed. The vegetative and reproductive development of the grapevines, as well as their susceptibility to fungal diseases in the field, wood and grape composition, and grape yield, were investigated. Individual variables were subjected to analysis of variance. Additionally, all variables were subjected to multivariate principal component analysis. Compared with plots under integrated management, plots under the two biological treatments were characterized by higher soil quality and lower vegetative growth and grape yield, and therefore higher exposure of grapes and lower grape cluster compactness, and, probably as a result of these morphological differences, lower incidence of acetic acid rot. Principal component analysis clearly differentiated the three treatments, and showed that biodynamic management had more pronounced effects than organic management in terms of enhanced soil fertility and reduction of vegetative growth. Conclusions: In the present study, organic and especially biodynamic management resulted in a morphology favouring production of high-quality grapes. The treatments differed in terms of fertilization and plant protection methods as well as choice of cover crops. Therefore, further research is necessary with respect to root growth and the nitrogen and water uptake dynamics of vines and cover crops. The differences between grapes produced under organic and biodynamic management emphasize the need for more research on the mode of action of biodynamic preparations. Significance and impact of the study: In recent years, both winegrowers and consumers have expressed steadily growing interest in organic and especially biodynamic wine production. The present study contributes to a better understanding of the effects on grapevine growth and morphological development of shifting to these methods as a way to increase product quality.