Rootstock-Scion Interactions Concerning Wine Making. I. Juice Composition Changes and Effects on Fermentation Rate with St. George and 99-R Rootstocks at Two Nitrogen Fertilizer Levels

Abstract

The brush-wt/crop-wt ratio as influenced by rootstock and fertilizer treatment can be correlated to the chemical composition of the grapes. An analysis of covariance of regression data of the ogarithm brush wt/crop wt to total nitrogen in the juice indicated that this relationship was independent of variety with respect to principal (slope of regression lines). It was postulated that the significant elevation changes in these regression data were due primarily to leaf-area brush-wt variety differences or differences in pruning. The more vigorous rootstock (`St. George') yields fruit with more total nitrogen, total acid, tannin, potassium phosphorus, ammonia, and biotin, and a higher pH. The ammonium nitrate treatment had only a small effect, the only significant response being an increase in total nitrogen in the juice for the treated vines. A significant effect of year X fertilizer on ammonia content of the juice was found. The choice of rootstock for a wine variety can alter the juice composition significantly and thus affect the fermentation rate of the must to an economically important degree.