Predicting grapevine canopy nitrogen status using proximal sensors and near-infrared reflectance spectroscopy

Background: The current method employed by industry for tissue analysis to determine grapevine nitrogen (N) status is expensive and time intensive. Aims: This study explored the use of proximal sensors and Fourier transform near infrared spectroscopy (FT-NIRS) to predict vine (Vitis vinifera L.) canopy N status over two growing seasons in Southern Tasmania, Australia. Methods: The GreenSeeker, Crop Circle ACS-430 and SPAD-502 proximal sensors were used to measure vine canopies (cv. Pinot Noir and Chardonnay) at three sampling dates (January, February, March) in the 2017/18 growing season, and two (December & February) in the 2018/ 19 growing season. For 12 replicates consisting of 5 vines each, a 30-leaf sample was taken for FT-NIRS and elemental analysis on dried, ground leaf samples. In addition, measurements with a portable FT-NIRS were taken on fresh leaf samples (2018/19). All measurements were correlated with leaf N concentration (%) determined via elemental analysis. Results: The reliability of the proximal sensors to predict vine N content was dependent on the vine variety and sampling time. FT-NIRS demonstrated a strong ability to predict vine N concentration independent of season, sampling time and variety. The benchtop FT-NIRS showed the strongest predictability over both seasons (r2 = 0.94), yet the portable FT-NIRS also showed potential (r2 = 0.76). Conclusion: Further investigation of portable FT-NIRS technology is necessary to provide a robust model for non-destructive vine N determination in the field.