Optimising nitrogen management for cool climate vineyards

Nitrogen (N) is an essential nutrient for vine health, as it contributes to shoot and bunch development and serves as an important nutrient source for yeast to convert juice to wine during the fermentation process. In most commercial vineyard operations, supplementary N from synthetic fertilisers is necessary to guarantee sufficient yields. Excess N can however result in unbalanced vines, promoting vegetative growth at the expense of fruit quality. Supplied N that is not taken up by vines can result in negative environmental consequences, such as the contamination of groundwater and waterways, and the release of the potent greenhouse gas nitrous oxide. The majority of N research that has previously been performed has been in warm, Mediterranean climates. However, these findings are not always applicable to cool climate vineyards. As plantings in cool climate wine regions increase due to the changing climate, further work is necessary to determine appropriate N fertilisation guidelines. This thesis serves to provide guidelines for successful N fertilisation strategies in cool climate wine regions based on a better understanding of vine nitrogen physiology, more efficient nitrogen fertigation practices in the field, and an evaluation of vine N prediction methods. i) Physiology of vine nitrogen uptake, partitioning, and remobilisation The timing of N application can have a significant impact on vine N status and where N is partitioned and stored in the vine. The first chapter of this thesis explores how four N fertiliser application timings (evenly spread, budbreak ‚Äö- bloom, bloom ‚Äö- veraison, veraison ‚Äö- harvest) impacts NUE, N storage (perennial components), and N remobilisation in 1 year old potted Vitis vinifera L. cv. Pinot Noir using labelled 15N over two consecutive seasons in a cool climate wine region. The veraison to harvest (VH) treatment resulted in less vigorous (reduced dry matter) and less productive vines. N application timing did not impact fertiliser N uptake by perennial vine organs, yet a decrease in overall vine fertiliser uptake and reduced NUE was observed in the VH treatment due to differences in the N uptake of annual organs. No significant differences between vine N uptake of the other N application timings, or organ partitioning between treatments, was observed. ii) Fertigation practice in the vineyard One of the main challenges in cool climate winemaking is to reach acceptable (>140 mg N L\\(^{-1}\\)) yeast assimilable N (YAN) concentrations, without increasing vine vigour and negatively impacting wine composition. Yet very few studies have observed the impact of N fertiliser rate from the vine through to the finished wine. The second chapter of this thesis focuses on how N application rate (0, ~18, ~36 kg N ha\\(^{-1}\\)) and irrigation (commercial and double commercial rates) impacts vine vigour, vegetative growth, yield, grape/juice composition and wine composition in Vitis vinifera L. cv. Pinot Noir and Chardonnay over three consecutive growing seasons. Increasing N rate significantly improved YAN concentrations across both varieties in 2 out of 3 growing seasons, with the 36 kg N ha\\(^{-1}\\) rate associated with increasing YAN to acceptable levels. Irrigation had no significant impact on YAN concentrations. Treatment influences on vine vegetative growth, yield, and grape and wine composition were marginal and inconsistent, and were largely influenced by climatic conditions. iii) Non-destructive predictability of vine canopy N status The ability to monitor N rates throughout the season, and adjust when necessary, is an important part of successful fertilisation management. Leaf tissue analysis is the current method employed by industry to determine grapevine N status, yet it is destructive, expensive and time intensive. The wine industry would benefit from a rapid, non-destructive method to estimate vine N status in the field. The third chapter of this thesis investigates the ability of commercial sensors (GreenSeeker, Crop Circle ACS-430, SPAD-502) and Fourier transform near infrared spectroscopy (FT-NIRS; benchtop and portable) to predict vine leaf N concentration in Vitis vinifera L. cv. Pinot Noir and Chardonnay, through comparison to the industry standard method of leaf elemental analysis over two consecutive growing seasons. The reliability of the proximal sensors to predict vine N content was dependent on variety and sampling time. FT-NIRS demonstrated a strong ability to predict vine N content independent of season, sampling time and variety. Benchtop FT-NIRS showed the strongest predictability over both seasons (r\\(^2\\) = 0.94, RMSECV = 0.071 ‚Äö- 0.104, RPD = 3.88 ‚Äö- 4.05), yet the portable FT-NIRS also showed potential (r\\(^2\\) = 0.76, RMSECV = 0.205, RPD = 2.03). These findings provide tangible options for cool climate growers to improve N resource management and wine composition. Practical cool-climate wine region N fertiliser recommendations and future research directions are discussed.