Survey of the Nitrogen Nutrition of Chasselas and Petite Arvine Musts in the Valais

A survey conducted by the Experimental Station for Viticulture and Oenology has furthered our understanding of nitrogen nutrition management practices in the vineyard and wine cellar for the Chasselas and Petite Arvine grape varieties in the Valais, highlighting potential avenues for improvement.

In 2023, a questionnaire was sent to the producers of the Vitival network in the Valais regarding the 2022 vintage. Forty-six wine estates in the Valais took part, responding to several questions concerning their practices both in the vineyard and in the cellar.

The results show that few producers apply foliar nitrogen and measure the assimilable nitrogen in the musts. This could explain sluggish fermentation, particularly in the case of Petite Arvine.

Application of foliar nitrogen to vines and analyses of assimilable nitrogen in musts not common

In 2022, the majority of individuals surveyed (89% for Chasselas, 85% for Petite Arvine) did not apply foliar nitrogen to their vines (a practice prohibited in organic and biodynamic agriculture, and not very widespread in conventional viticulture) (Figure 1).

Scarcely one-quarter of respondents analysed the assimilable nitrogen in the must (Figure 2). Over 60% of the analyses showed a content of under 140 mg/L, the recommended threshold for achieving alcoholic fermentation (AF) within a reasonable period of time based on sugar concentration and oenological practices. 

Petite Arvine affected by sluggish alcoholic fermentation

In response to the question on stuck or sluggish AF, Petite Arvine appears to be more affected than Chasselas, accounting for 54% of cases versus 18% for Chasselas (Figure 3). Grape variety is one of the factors that may influence the nitrogen content of the musts, which could explain the higher occurrence of fermentation slowdown in the case of Arvine. Moreover, due to the concentration of assimilable nitrogen present in the must, sluggish fermentation due to a lack of assimilable nitrogen may also affect the aromatic quality (i.e. the fine bouquet) of the wines.

Inputs usually applied at the start of alcoholic fermentation

According to the findings of the questionnaire, one-third of the participants use nitrogen-based inputs at different stages of AF. The results show that the majority of respondents add these inputs when yeast is added (24% for Chasselas, 22% for Petite Arvine) and in the first third of AF (33% for Chasselas, 22% for Petite Arvine). Use is less frequent in the middle of and at the end of AF. Ammonium phosphate is the nitrogen-containing input most commonly used by the participants.

Participants were also questioned on the use of non-nitrogen inputs over the course of AF. The findings show that these inputs are applied mainly in the first phase of fermentation, particularly upon the addition of yeast (11% for Chasselas, 13% for Arvine) and one-third of the way into AF (15% for Chasselas, 11% for Arvine). In the middle and at the end of AF, non-nitrogen inputs are seldom applied, if at all. Generally speaking, the most commonly used inputs are sugar in the rehydration phase, yeast hulls, inactivated yeast, enzyme preparations and tartaric acid.