Nitrogen nutrition status of the vine: correlation between N-tester and SPAD chlorophyll indices

Knowledge of the nitrogen nutrition status of the vine is essential for long-term management of its nutrition with the aim of producing high-quality grapes. Measurement of the chlorophyll index is a fast, non-destructive and relatively inexpensive method that provides a good approximation of the nitrogen nutrition status of the vine during the growing season. Several chlorophyll meters are available on the market, each using its own measurement unit. With the aim of popularizing the use of chlorophyll meters, the interpretation thresholds of the SPAD index, measured on the vine at the veraison stage, have been established from correlation with the N-tester index, for which the thresholds are already known

Carryover effects of crop thinning and foliar N fertilisation on grape amino N composition

This article is published in cooperation with Terclim 2022 (XIVth International Terroir Congress and 2nd ClimWine Symposium), 3-8 July 2022, Bordeaux, France.Nitrogen (N) is an essential element for vine development and yield; it is also involved in the winemaking process and significantly affects wine composition. It is therefore essential to control and optimise plant N use to ensure an adequate N composition of the grapes at harvest. An improved understanding of the impact of cultivation practices on plant N metabolism would allow a better orientation of technical choices with the objective of quality and sustainability (i.e., fewer inputs, more efficiency).Our trial focused on the impacts of fertilisation and crop thinning on grape N composition. A wide crop load gradient was set up in a homogeneous plot of Chasselas (Vitis vinifera L.) in an experimental vineyard in Switzerland. Foliar urea was applied at veraison in order to compare it with an unfertilised control. Vine development and grape composition were evaluated over two years, with particular attention to the carryover effects of both fertilisation and crop thinning.Foliar N fertilisation effectively increased the amount of N in grapes at harvest in the same year, but had no impact on grape ripeness or carryover effect on year n + 1. Conversely, crop thinning improved grape maturity by reducing fruit N and C demand. Interestingly, amino N proportions could be distinguished according to crop load, while the global grape N concentration at harvest remained unchanged. Some amino acids were more affected by crop thinning than others. The concentrations of alanine, γ-aminobutyric acid (GABA), serine and threonine were reduced by crop thinning. Crop thinning had a strong carryover effect on year n + 1. The carryover impact of crop thinning on grapes in terms of both maturation index and N composition could be observed at the onset of grape ripening on year n + 1.This experiment highlighted the influence of the previous year’s agricultural practices on grape C and N accumulation before and during the ripening phase. Consequently, the modulation of grape composition at harvest should be considered over two consecutive years. These results will contribute to the improvement of predictive models and sustainable agronomic practices in perennial crops

Intensity and timing of defoliation on white cultivar Chasselas under the temperate climate of Switzerland

Aim: The objective of this work is to investigate the effects of early defoliation on cv. Chasselas under the temperate conditions of Switzerland, with particular attention to berry anatomical traits and wine sensory parameters. Methods and results: Defoliation (removal of 6 basal leaves + 6 lateral shoots per shoot) was completed during three developmental stages of grapevine, i.e., pre-flowering, late flowering and bunch closure, and at two intensity levels. The experimentation was performed repeatedly over four years. In addition to vintage effect, pre-flowering defoliation had a consistent impact on vine agronomic behaviour. The yield was highly affected by the technique (more than 30% loss). Earlier and more intense defoliation had more impact on yield, while post-berry-set defoliation had no effect on yield. Intensive defoliation also modified berry skin thickness and had a positive impact inhibiting Botrytis development. Wine composition and sensory analysis were not affected by the practice. However, pre-floral defoliation affected bud fruitfulness and vigour, i.e., trimming and pruning weights. This result noted a carryover effect that could affect vine sustainability under restrictive conditions. Conclusion: In the context of this study, pre-flowering defoliation seems to be an interesting practice to reduce vigour and control the high production potential of the cv. Chasselas. The intensity of early defoliation allows for the modulation of the impact on the yield in order to prevent excessive yield loss. Significance and impact of the study: Pre-flowering defoliation of the white cultivar represents a prophylactic solution to reduce both chemical entrants and bunch-thinning costs

Assessment of plant hydraulics in grapevine on various "terroirs" in the Canton of Vaud (Switzerland)

Aims: The aim of this paper is to study the relevance of different physiological indicators concerning vines hydraulic in relation to estimations of the soil water reservoir on various « terroirs » in Switzerland. Methods and results: Different physiological indicators like leaf and stem water potentials, carbon isotope discrimination and a model of transpirable soil water were used. A close relationship was observed between pre-dawn leaf water potential and the soil water holding capacity (SWHC) from about thirty study sites over a period of three years. Conclusion: The different assessments of plant hydraulics (leaf water potential, carbon isotope discrimination technique, model of transpirable soil water) were in good agreement with the soil water holding capacity. Significance and impact of study:The results confirm the importance and the possibilities to estimate plant water ability in relation with soil water holding capacity and climatic factors

Nitrogen dilution in excessive canopies of Chasselas and Pinot noir cvs

Aims: The impact of canopy management on the nitrogen (N) content in grapevines was studied. Methods and Results: Two trials were carried out between 2001 and 2010 on Vitis vinifera cvs. Chasselas and Pinot noir. The observed factors of variation were the intensity of lateral shoot removal for the first trial and the severity of shoot trimming for the second trial. The N content was evaluated in parallel by leaf diagnosis, the chlorophyll index and the yeast available N concentration (YAN) found in the musts. When the yields were the same, a significant dilution of N in proportion to the development of the leaf area was revealed. Treatments resulting in excessive leaf area presented N deficiency in the leaves and the musts. Conclusion: The N content in both the vines and grapes was influenced by the canopy management (lateral shoot removal and shoot trimming), and the magnitude of the response appeared to be even greater in the absence of water stress. In addition, the risk of N deficiency was found to increase beyond a maximum value of the leaf-fruit ratio. Significance of the study: Canopy management has a significant influence on the N content in foliage and grapes, and the risk of N deficiency increases under a situation that produces an excessive leaf area

Vine water status as a parameter of the « terroir » effect under the non-irrigated conditions of the Vaud viticultural area (Switzerland)

Aims: The aim of the study was to assess whether, for vineyards in Vaud (Switzerland), vine water status might be a major natural factor in determining wine sensory characteristics, i.e., responsible for the so-called « terroir » effect. Methods and Results: The impact of vine water status on fruit and wine characteristics was examined for 23 non-irrigated locations with different soil water holding capacities during three seasons (2007-2009). In 2009, a close relationship was observed between δ13C and soil water holding capacity. Furthermore, the level of vine water status influenced both fruit and wine composition. Berry weight was strongly correlated to vine water status. The highest grape soluble solids content (SSC) at harvest was reached when water deficit was mild. Wine colour was related to vine water status: wine made from grapevines with low water status showed a significantly higher colour density. However, sensory analysis did not discriminate between wines from different water conditions. Conclusion: In a dry year like 2009, vine water status was related to soil water holding capacity and determined grape and wine characteristics. However, no clear relationship was observed between wine sensory characteristics and vine water status. Significance and impact of the study: This study confirms the importance of soil in determining grape and wine characteristics through its effect on vine water status

Soil parameters impact the vine-fruit-wine continuum by altering vine nitrogen status

Aims: A three-year study was conducted in the Vaud vineyards of Switzerland to evaluate the effects of « terroir » on the ecophysiology and fruit composition of Vitis vinifera L. cv. Doral (a white variety) and the characteristics of the produced wine. Methods and results: The impact of soil on the vine-fruit-wine continuum was evaluated at 13 sites during three seasons. Except for soil, the vineyards presented almost identical climatic characteristics and used similar cultivation techniques. We monitored the nitrogen status of the vines by measuring yeast assimilable nitrogen (YAN) in the must. The soil modulated vine nitrogen status by its fertility and rooting depth. Low vine nitrogen status induced a high soluble solid content, low malic acid content, and high pH in fruits and resulted in small berries and low vine vigour. Wines were produced in a standardised manner from each site; then, they were subjected to sensory and chemical evaluation. YAN in musts was the parameter that best explained the variation in wine sensory characteristics. Wines made from grapes with low YAN values had negative sensory characteristics such as astringency and low aromatic complexity. Conclusion: This work provided evidence of how soil can influence fruit composition and the sensory attributes of wine. Vine nitrogen status in relation to soil characteristics was a key parameter contributing to the terroir effect. Significance and impact of the study: This study focuses on the whole vine-fruit-wine continuum and uses scientific rigour to investigate the terroir effect over a number of vintages. Key words: terroir, vine nitrogen status, soil effect, wine quality, vinefruit- wine continuu