Reakcija tla jedan je od najznačajnijih čimbenika koji utječu na topljivost i pristupačnost hraniva biljci. Provedeno istraživanje imalo je za cilj utvrditi u kojoj mjeri reakcija tla utječe na K/(Ca+Mg) u lišću vinove loze (Vitis vinifera L.), sorta Sauvignon bijeli (podloga SO4) na području Plešivičkog vinogorja (sjeverozapadna Hrvatska). Istraživanja su provedena u razdoblju 2009.-2011. godine na području Plešivičkog vinogorja na tlima jako kisele do kisele reakcije (lokacija Rečki gaj: pHKCl 3,54-5,01) i na tlu alkalne reakcije (lokacija Borička: pHKCl 7,01-7,41). Uzorci lišća za praćenje dinamike kalija, kalcija i magnezija te njihovog međusobnog odnosa uzimani su tri puta tijekom vegetacije (fenofaza cvatnja, šara i berba) u sve tri godine istraživanja. U sve tri godine istraživanja značajan utjecaj na K/(Ca+Mg) odnos u lišću vinove loze imala je reakcija tla te fenofaza rasta i razvoja. Širi odnos K/(Ca+Mg) u lišću vinove loze, u svim godinama istraživanja utvrđen je na tlu kisele reakcije (0,29, 0,58, 0,59) u odnosu na alkalno tlo (0,20, 0,40, 0,38). Najširi kationski odnos utvrđen je u fenofazi cvatnje (0,31-1,02), a najuži u fenofazi berbe (0,15- 0,34) u svim godinama istraživanja neovisno o reakciji tla.; Soil reaction is one of the most important factors that affects solubility and availability of nutrients to plants. The aim of the present research was to determine the effect of soil reaction on the K/(Ca+Mg) ratio in the grapevine (Vitis vinifera L.) leaves of the cultivar Sauvignon Blanc (rootstock SO4) in the Plešivica wine growing region (Northwest Croatia). The research was conducted in the period 2009-2011 in the Plešivica wine growing region on very acid to acid soil (location Rečki gaj: pHKCl 3,54-5,01) and on alkaline soil (location Borička: pHKCl 7,01-7,41). Leaves samples for monitoring the dynamics of potassium, calcium and magnesium and their mutual relationship, have been taken each year three times during vegetation (in the following phenological stages: flowering, veraison and harvest). A significant effect on the K/(Ca+Mg) ratio in the grapevine leaves was determined in respect to soil reaction and the phenological stage in all three years of research. The wider ratio of K/(Ca+Mg) in the leaves in all three years was determined on the acidic soil (0.29, 0.58, 0.59) in respect to alkaline soil (0.20, 0.40, 0.38). The widest cation ratio was determined in the stage of flowering (0.31-1.02) while the most limited ratio was determined in the stage of harvest (0.15-0.34) in all research years regardless soil reaction.