The pedoclimatic conditions impact the yeast assimilable nitrogen concentration in the grapevine must and the valorisation of foliarnitrogen fertilisation

Aims: Agroscope investigated the efficiency of nitrogen fertilisation via foliar urea application at veraison with the aim of raising the yeast assimilable nitrogen (YAN) concentration in the musts. The observations were conducted over three vintages on two grapevine cultivars in several pedoclimatic conditions of the Leman wine region, Switzerland. Knowing that the YAN in the must plays a key role in wine quality, the aim of this study was finding the main parameters affecting the final YAN level in order to better control them.

Methods and results: Five plots of Doral (white grape, Chasselas x Chardonnay) and five plots of Gamaret (red grape, Gamay x Reichensteiner) were chosen over 80 km of vineyards. Pedologic profiles were realised. Vegetal materials, date of plantation and cultivation practices were kept constant for comparison purposes. Each plot was divided in two treatments of 60 vines each: a control treatment and a nitrogen fertilized treatment (20 kg N/ha as foliar urea applied at veraison). Phenological development, nitrogen status and grape maturation of vines were monitored. 50 kg of grapes from each treatment were harvested and then vinified separately using a standard protocol. YAN levels in musts were significantly enhanced by foliar-nitrogen fertilisation, but strong vintage, site and cultivar effects were pointed out: average YAN gain over 3 years was 69 ± 32 mg N/L in Doral must and 52 ± 27 mg N/L in Gamaret must. Some sites consistently presented higher gains (e.g. Doral at Villeneuve, +106 mg N/L). The bigger water holding capacity and the deeper effective root zone seemed to mainly enhance vine nitrogen status. No correlation could be established between initial leaf N content and the variation of YAN gain. YAN in must was the parameter that best explained the positive variations in wine sensory characteristics and, in the case of Doral only, was highly correlated to the overall appreciation of the wines (R2 = 0.70).

Significance and impact of the study: This work confirms that YAN level in must, in relation to climate and soil characteristics, contributes to the terroir effect on the wine quality. YAN concentration is clearly influenced by pedoclimatic conditions and cultivar. The impact of foliar-N supply is not always sufficient for a significant improvement of wine overall appreciation particularly for the cv. Gamaret. This observations may assist the development of sustainable practices to increase the YAN concentration in musts.