Radiative and thermal effects on fruit ripening induced by differences in soil colour

One of the intrinsic parts of a vineyard “terroir” is soil type and one of the characteristics of the soil is it’s colour. This can differ widely from bright white, as for some calcareous soils, to red, as in “terra rossa” soils, or black, as in slate soils. The aim of this study was to assess how soil colour can influence vineyard microclimate and fruit properties including aroma precursors. After flowering, (BBCH 79) a loess-type soil (control) was covered with a thin layer of three different materials: a) black coarse slate, b) red clay brick, and c) white pumice. The vines (Vitis vinifera L. cvs. Riesling and Pinot noir) were trained to a vertical shoot positioning (VSP) system. Surface colour had significant effects on the quantity and quality of reflected radiation into the fruiting zone. The pumice covered soil showed the highest amount of reflected – and the highest ratio of red-to far red light, important in phytochrome mediated enzyme activity in the fruit.
Large thermal effects on soil surface temperature and on berry skin temperature were found. By varying the distance of clusters to the ground, the temperature of berry skins declined rapidly within the first 0.3 m when fruit was exposed to the red, white or natural coloured soil. In contrast, over coarse ground slate the absolute berry surface temperature was higher and remained constant over the same distances. Berry ripening was affected by surface colour and preliminary results indicate that altered vineyard microclimate has effects on berry composition.