Effects of the Annual Nitrogen Fertilization Rate on Vine Performance and Grape Quality for Winemaking: Insights from a Meta-Analysis

Figure 7

Contour plots of the density surfaces for which either the Mitscherlich law or a logistic curve could be reasonably fitted to the ridgeline points. The fitting was obtained by density-weighted generalized reduced gradient (GRG) nonlinear optimization of the sum of squared deviations between calculations and observations of the trial-normalized grape quality parameters. (a) Anthocyanin concentration. (b) Total polyphenol index. (c) Yeast assimilable nitrogen.

(a)

(b)

(c)