2018 ASHS Annual Conference

Nitrogen fertilization is a little studied area of hard cider apple (Malus x domestica Borkh.) production that potentially impacts tree growth, yield, fruit polyphenol concentration, yeast assimilable nitrogen in juice, and fermentation kinetics. In the spring of 2016, a multi-year nitrogen fertilization study was started on two-year old Golden Russet and Medaille d’Or tall spindle trees on G.30 rootstock in Ithaca, NY. Low (28 kg·ha^-1 N), medium (56 kg·ha^-1 N), and high (112 kg·ha^-1 N) nitrogen fertilizer treatment rates, plus an unfertilized control, were implemented by applying calcium nitrate granular fertilizer each spring. Greater nitrogen fertilizer rates resulted in increased tree size, as measured by trunk cross sectional area (TCSA) and central leader growth for both cultivars. In 2016, the low, medium, and high treatments had 28%, 25%, and 26% greater TCSAs than the control, respectively, and leaders were 36%, 46%, and 31%, longer than the control, respectively. In 2017, the high nitrogen fertilizer treatment increased TCSA by 66% relative to the control, but no other differences in tree growth were found for either cultivar. No differences in leaf nitrogen content were found among treatments for either cultivar in 2016 or 2017. Nitrogen fertilization advanced fruit maturity during the 2017 harvest. When data for both cultivars were analyzed in a single statistical model, fruit from the medium and high nitrogen treatments had an average of 0.5 and 0.8 greater starch index measurements than the control. Fruit from the high nitrogen treatment had 15% lower firmness than the control, and the high and medium nitrogen treatments had 8% and 17% lower delta absorbance reading (chlorophyll content). No differences in juice polyphenol content were found in 2017, as measured by the Folin Ciocalteu assay. Golden Russet juice from the high nitrogen treatment had 43% greater yeast assimilable nitrogen than the control. During fermentation of the Golden Russet juice, the unfertilized control produced more hydrogen sulfide (a negative attribute) than fermentations from the low and high treatment fruit. This preliminary data suggests that nitrogen fertilization in the orchard impacts tree growth, fruit quality, and fermentation kinetics. However, additional years of data are needed to determine the consistency of these results.