The effect of pedoclimatic conditions on the yeast assimilable nitrogen concentration on white cv. Doral in Switzerland

Aims: Agroscope investigated the efficiency of nitrogen fertilization via foliar urea application at veraison with the aim of raising the YAN (yeast assimilable nitrogen) content in the musts. The observations were conducted on the white grapevine cultivar Doral (Chasselas x Chardonnay) in several pedoclimatic conditions of the Leman wine region, Switzerland, in the years 2012 and 2013. Knowing that the YAN in must plays a key role in wine quality, the aim was finding the main parameters affecting the final YAN level in order to better control them.

Methods and results: Five plots of Doral 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/ha as foliar urea applied at veraison). Phenological development, nitrogen status and grape maturation of vines were monitored. 50 kg of grapes were harvested in each treatment. Musts were analysed after crushing and then vinified separately using a standard protocol. Wines were then analysed and tasted by an expert panel. Strong vintage and site effects were pointed out. YAN levels in musts were significantly affected by nitrogen fertilization. YAN gain in must was 56 ± 31 mg/L average. YAN gain between control and fertilised treatments was globally higher in 2013. Some sites consistently presented higher gains. The soil seemed to mainly affect vine nitrogen status by its water holding capacity and its effective root zone depth. 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, although not always significant.

Significance and impact of the study: This work has so far confirmed 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 (i.e. vintage and site). The study is ongoing in 2014 in order to better understand which parameters in the vineyard we could optimize with the aim of raising up the YAN level in musts.