Comparison of vineyard nitrogen application practices and winery nitrogen management

Abstract

The timing of Nitrogen (N) application is critical for altering vine development, the N directed to berries and reserves. Stress on the vine, or nutrient and irrigation management, might give the accumulated reserves a critical role during grape maturation in the following season, influencing berry composition and wine quality. The aim of this project was to clarify the link between N input and reserves on fruit and wine composition under different environmental conditions. A Semillon field trial was conducted in South Eastern Australia over two growing seasons. N fertiliser was applied at 0 and 50kg/ha and either at bloom or after harvest. These N treatments were combined with moderate water stress applied from two weeks before veraison for four weeks or without water stress applied. Berries were collected during ripening to investigate the accumulation of N compounds and other compositional changes within the fruit. Wood and root samples were collected to determine the influence of N reserves on grape maturation. Different N and water supply regimes influenced vine performance in both seasons. Water stress lowered yield due to reduced berry size and increased sugar accumulation in the fruit. However, interactive effects of N supply at bloom and later water stress resulted in decreased sugar concentrations in berries at harvest.

Root N levels generally decreased for N0 treatments during the experiment, while post-harvest N application elevated root N till bloom. The N status of vines affected the form and concentration of must nitrogenous compounds. Yeast available nitrogen (YAN) increased during ripening and affected fermentation kinetics through winemaking. N application increased YAN levels, while N deficiency resulted in delayed and sluggish fermentations in both seasons. The adjustment to a common YAN level with diammoniumphosphate (DAP) to all musts reduced fermentation times. But the impact of delayed and slower fermentation rates due to vineyard N deficiency was still present in the YAN adjusted batches. Different vineyard management practices altered N reserves and ultimately vine performance. The results also indicate a limited effectiveness of N supplementation in the winery and suggest further benefits from optimisation vineyard N management.