DIFFERENTIAL-EFFECTS OF CANOPY MANIPULATION AND SHADING OF VITIS-VINIFERA L-CV CABERNET-SAUVIGNON - PLANT NUTRITIONAL-STATUS

The effects of canopy manipulation and shading on crop quantity and qu ality as well as plant physiology in Vitis vinifera have already been studied by many authors while the plant nutritional status changes ind uced by such treatments present many unexplained aspects. Partial clus ter and leaf removals were performed on Vitis vinifera L. cv. Cabernet Sauvignon at veraison (40% berries coloured) for two years to give fo ur treatments: Control (C), Cluster Thinning (CT), Leaf Removal (LR), and Cluster Thinned + Leaf Removal (CT+LR) plots. At veraison, one hal f of these plots were shaded using a 50% shading net. The correlations between elemental contents of different organs showed that only potas sium (K) in the leaves and stems were positively related, while for th e other macro- and micro-elements, no relationship or negative links w ere obtained. Shading needs only 14 days to modify the nitrogen (N) an d phosphorus (P) in leaves. At harvest, N was depressed in leaves of c luster-thinned vines and enhanced in leaf-removed ones. Such changes a re discussed on the basis of photosynthetic data which support the hyp othesis that canopy manipulation involves modifications in both leaf b iochemical and photochemical activities.