Effect of nitrogen and iron synergistic application on physiological growth, berry quality, and flavonoid content of wine grapes

This study evaluates and contrasts the concurrent application of nitrogen (N) fertilizer and diverse forms of iron (Fe) fertilizer on the physiological growth and components of wine grape berries. The objective is to provide both theoretical insights and practical support to enhance berry quality and optimize wine fermentation processes. Eight treatments were established encompassing two main treatments (without urea and with urea application) and four sub-treatments (ferrous sulfate, ferrous gluconate, EDTA-Fe, and ferric citrate). Results indicate that the synergistic application of N fertilizer and chelated Fe fertilizer significantly improves the photosynthetic characteristics of grape leaves, leading to a remarkable enhancement in leaf chlorophyll content (13.7–83.9%). Moreover, the combined application of N and Fe fertilizers significantly boosts berry tannin levels (11.2–21.5%), anthocyanins (2.8–117%), and total phenols (1.9–41.2%). Additionally, there is a notable increase in the relative abundance of amino acids and flavonoids, contributing to an augmented yield (3.9–36.1%). Correlation analysis suggests that the synergistic application of N and Fe improves berry quality by augmenting N and Fe content in the leaves, promoting photosynthesis, improving water-use efficiency, and increasing leaf chlorophyll content. Overall, the comprehensive score of the principal component analysis reveals that the synergistic application of N fertilizer and chelated Fe fertilizer has the most significant effect, leading to substantial improvements in the quality and yield of the berries. These findings provide critical theoretical support for future fertilizer strategies aimed at enhancing the quality and nutritional value of berries and wine.