POTASSIUM CONTENT OF GRAPEVINE DURING THE VEGETATIVE PERIOD - THE ROLE OF THE ROOTSTOCK

The role of rootstock in the potassium (K) content of Croatina grapevi nes was investigated in a replicated rootstock trial on a sandy clay l oam soil in Oltrepo Pavese, Italy. Each rootstock was significatively different in terms of K absorption ability. The effect of the seasonal weather on the level of must K was strictly linked to the rainfall du ring the vegetative period. The highest K levels were induced by roots tocks 44-53 M and SO4, while the lowest by rootstocks 140 Ru, 420A, an d 1202C. The rootstock effect on must K levels was particularly marked in the driest year when on average the K levels were the lowest. Pota ssium in musts and leaves at veraison was strictly correlated to must pH. The results indicated a different ability for K absorption, induce d by rootstock, which resulted either in high leaf or musts K levels. A considerable influence due to the seasonal weather course was eviden t too. The results provide evidence that vine K status can be controll ed to some extent with proper selection of rootstock, because of the l arge genetic diversity that can be exploited by rootstocks.