Effect of irrigation on changes in berry composition of Tempranillo duringmaturation. Sugars, organic acids, and mineral elements

The impact of water availability on the yield and must composition of Vitis vinifera L. cv. Tempranillo grapes was studied over a three-year period. G rape juice composition was compared during stages II and III of the berry g rowth. The object of this study was to ascertain the effect of irrigation r egime on berry development and ripening, and hence on grape juice quality. Changes in berry weight, degrees Brix, glucose, fructose, titratable acidit y, pH, tartaric acid, malic acid, citric acid, and mineral elements were mo nitored. The evolution of sugars and acids during berry growth followed pat terns similar to those reported by previous investigators. Hence, water ava ilability did not affect the accumulation patterns of the different sugars and acids. Glucose was the predominant sugar in the berries at veraison, wh ile fructose predominated at the end of ripening, irrespective of the treat ment applied. Organic acid concentration was highest when berries were pea- sized, and it began to decrease at veraison. The rate of decrease was great er for malic acid than for tartaric acid. The concentration of tartaric aci d was higher than that of malic acid from veraison on, and differences betw een them increased as ripening progressed. The differences between malic ac id and tartaric acid were greatest in the non-irrigated treatment. Total so luble solids, and the concentration of glucose and fructose were significan tly higher in the irrigated vines than in the non-irrigated vines, mainly t owards the end of ripening, except in 1992. In that year the values for the non-irrigated vines were slightly higher, though the differences were not significant on many sampling dates. The "Brix of the irrigated grapes at ha rvest were 2.8% to 14.9% higher than in the non-irrigated grapes. The large st increase in "Brix (67% - 124% in non-irrigated grapes and 58% -117% in t he irrigated grapes) took place after veraison. Titratable acidity (TA) was significantly higher for the irrigated vines, primarily at the end of ripe ning. The TA of irrigated vines at harvest was 9.8% to 28.3% higher than th e TA for non-irrigated vines. By expressing the data for glucose, fructose, tartaric acid, malic acid, and citric acid in grams per berry, we observed the largest number of sampling dates with significant differences between irrigation treatments in the years 1990 and 1992. The concentrations for th e mineral elements followed differing trends over the course of ripening. P otassium increased until harvest time, and calcium and magnesium decreased, but sodium did not exhibit any clear trend, rising or falling on different sampling dates. Quantitatively, the values for all the parameters studied in the non-irrigated vines tended to be equal to or greater than those in t he irrigated vines, even though per-berry quantities were higher in the irr igated vines. The results show that the effect of water deficits on the com position of the grape juice was more intense in the final year of the study , when the differences in soil water availability between treatments were g reatest. The results further suggest that the higher yields in irrigated vi nes did not have any adverse effect on grape must composition and hence on grape juice quality, because on the whole synthesis and accumulation proces ses were able to offset any dilution effects.