Effect of Crop Level and Drip Irrigation Scheduling on the Potassium Status of Cabernet Sauvignon and Carignane Vines and Its Influence on Must and Wine Composition and Quality

Abstract

Effects of crop level treatments and drip irrigation schedules on the potassium contents of grape leaves, must and wine of Cabernet Sauvignon and Carignane were studied in two field experiments and the relationships between potassium, must acids, wine pH, acidity, color, and quality assessed. The potassium status of the plant was better reflected by petiole than by blade contents and at pre-harvest better than at bloom time. Leaf, must and wine K were well correlated to each other. Antagonism between leaf K and Mg was found in irrigation scheduling and not in crop level treatments. K content rose with decreasing crop loads (crop level to pruning weight ratio) in Carignane and Cabernet Sauvignon and with increasing amount and frequency of irrigation in Cabernet, the effect being at least partially due to the crop load reduction by irrigation. All forms of tartrate and malate except the neutral tartrate salt and free malic acid were positively related to wine quality in the various crop level treatments. A positive rank correlation existed between potassium and must malic acid levels. The wine to must ratio of tartaric acid concentrations showed a positive rank correlation to must potassium levels, and this was attributed to the effect of K on tartrate precipitation. The relationships between K, acidity, pH and color were differently affected by crop load and irrigation, by the absolute K level and perhaps by the cultivars. A continuous reduction in the K status of the vines and wines indicated that in these soils an ample fertilization is necessary in order to replenish the amounts of K removed by the crop.