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

The role of rootstock in the potassium (K) content of Croatina grapevines was investigated in a replicated rootstock trial on a sandy clay loam 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 during the vegetative period. The highest K levels were induced by rootstocks 44-53 M and SO4, while the lowest by rootstocks 140 Ru, 420A, and 1202C. The rootstock effect on must K levels was particularly marked in the driest year when on average the K levels were the lowest. Potassium in musts and leaves at veraison was strictly correlated to must pH. The results indicated a different ability for K absorption, induced by rootstock, which resulted either in high leaf or musts K levels. A considerable influence due to the seasonal weather course was evident too. The results provide evidence that vine K status can be controlled to some extent with proper selection of rootstock, because of the large genetic diversity that can be exploited by rootstocks.