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INFLUENCE OF N-SUPPLY AND SOIL MANAGEMENT ON THE NITROGEN COMPOSITION OF GRAPES
However, in recent years severely reduced concentrations of free amino nitrogen (FAN) were found.
These findings are relevant in connection with fermentation problems and changes in wine flavor.
There is a strong correlation between the nitrate supply of the soil and these observations.
All plant production measures which intensify reduced nitrogen and water supply, increase the risk of incomplete accumulation of amino acids in berries.
In the Rheingau region (Germany) these effects were present, whether the nitrate supply of the soil was insufficient or by altering the soil management system of vineyards with the cultivar ‘Riesling’. Amino acid concentrations in grapes from vineyards with cover crops were significantly reduced.
Furthermore a specific reduction in the concentration of arginine and glutamine occured.
The proline concentration remained constant, thus the percentage amount rose with decreasing nitrate supply of the soil.
In warm, dry years musts show high protein concentrations, resulting in reduced amounts of amino acids.
In northern, cool climate wine growing regions this effect of the vintage has a strong influence on the nitrogen assimilable by yeasts.
Furthermore, the described effects are influenced by N-reserves in woody vine parts, vine planting distance (plants per ha), canopy management, vintage (year), infestation with Botrytis sp. and the date of harvest, respectively.
Especially with regard to increasing negative aroma modifications, which are discussed in connection with abiotic and biotic stress, the amino acid concentration in grapes can serve as an important stress indicator.