Carryover Effects of Yield Regulation Practices on Grape Nitrogen Composition
Photo: Thibaut Verdenal, Agroscope
A study conducted on Chasselas vines in Switzerland shows the effects of yield regulation practices on grape ripening and nitrogen composition and suggests a two-year approach for optimising quality and sustainability.
Nitrogen is an essential element for vine development and yield. It is also involved in the vinification process and substantially influences wine composition. It is therefore essential to monitor and optimise plant nitrogen use to guarantee suitable grape composition at harvest while steering technical choices towards minimising input losses with the aim of supporting sustainability.
In 2017-2018 we tested the combined effects of fertilisation and yield regulation on grape nitrogen composition on Chasselas vines. Two yield levels were implemented: for each level, foliar urea was applied at veraison for comparison with a non-fertilised control. Yield regulation consisted of fruit thinning at the ‘bunch closure’ stage. Vine development and grape composition were evaluated over two years.
Crop thinning influences grape composition over at least two consecutive years
Foliar fertilisation with urea at veraison increased the amount of nitrogen in grapes at harvest in the same year, but had no impact on grape ripeness or carryover effect on year n+1.
Thinning, for its part, encouraged grape maturity in the same year by reducing nitrogen and carbon demand without impacting nitrogen concentration. Thinning also encouraged building reserves of these same nutrients in the roots. The following year, differences were observed from the veraison stage onwards: under low-yield conditions, total soluble sugars (TSS) were higher (+25%), and titratable acidity was lower (−18%) (Figure 1). Conversely, the yeast-assimilable nitrogen concentration was constant in the fruits regardless of plant fruit load. Only the proportion of amino acids varied, allowing the musts to be distinguished according to fruit load (Figure 2).
This experiment highlighted the influence of the previous year’s yield regulation practices on carbon and nitrogen accumulation in the grapes. Consequently, the modulation of grape composition at harvest should be considered over two consecutive years.
Conclusions
- Yield regulation strongly influenced grape composition for at least two consecutive years.
- Vines reduced both nitrogen uptake from the soil and mobilisation of nitrogen from reserves (i.e. primarily in the roots) in response to the lower demand for nutrients following fruit thinning.
- Vineyard nitrogen management should be considered from a multiannual perspective to optimise grape and wine quality whilst promoting sustainable agricultural practices.
Bibliographical reference
Carryover effects of crop thinning and foliar N fertilisation on grape amino N composition.
