Background and aim:
The presence of certain forms of nitrogen in grape must at harvest is necessary to ensure a smooth fermentation and has an influence on the final quality of the wine. A trial was set up to show the impact of the trimming height on the nitrogen composition of the must at harvest and on nitrogen fertilization efficiency.
The trial was set up in the Agroscope experimental vineyard in Pully, Switzerland. In a uniform plot of Chasselas, two variable factors were put in place: fertilization (two levels: an unfertilized control and addition of 20 kg/ha of leaf urea at veraison), and canopy height (three levels, 80, 120 and 150 cm). Canopy height was controlled by varying the trimming height. The trial was repeated for four consecutive years (2013–2016). The musts were analyzed at the time of harvest. The exposed leaf area (in m2) was estimated in August on a fully developed canopy.
Results and significance of the study:
The leaf-to-fruit ratio is an essential criterion for the physiological balance of the plant, for both carbon and nitrogen. The canopy height did not influence the efficiency of leaf fertilization. Nevertheless, a leaf-to-fruit ratio < 1.0 m2/kg was not sufficient to guarantee a proper grape maturity each year. Conversely, a leaf-to-fruit ratio > 1.5 m2/kg resulted in a moderate yeast assimilable nitrogen deficiency in the must. The leaf area had no influence on the amount of nitrogen assimilated by the plant. The amount of nitrogen in the plant therefore remained constant and hence its concentration was reduced in the volume of the biomass. In the temperate climate of the Swiss vineyard, a leaf-to-fruit ratio of 1.0–1.2 m2/kg is therefore recommended to guarantee full grape maturity, a suitable must nitrogen concentration and a sufficient nitrogen refill by storage organs. Good canopy management represents a sustainable solution that limits nitrogen deficiency in the must while minimizing the need for fertilization.
Thibaut Verdenal, Vivian Zufferey, Mélanie Huberty, Claire Melot, Ágnes Dienes-Nagy, Jean-Laurent Spring. (2021). Leaf area management affects grape nitrogen content. IVES Technical Reviews – published October 2021.
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