Developing a rapid assessment technique to determine grapevine canopy nitrogen status

The industry standard method to determine grapevine canopy nitrogen (N) status is through leaf and petiole tissue analysis. The accepted method is destructive, expensive and the results often require technical assistance to interpret. A rapid and simpler method to predict vine canopy N status would be beneficial to the viticultural industry. The utilization of proximal sensors (GreenSeeker, Crop Circle ACS-430 and SPAD-502) and near-infrared spectroscopy (NIRS) to predict vine canopy N content was explored in Vitis vinifera 'Pinot Noir' and 'Chardonnay' cultivars in Southern Tasmania, Australia. The measurements were correlated with leaf N content (%) obtained from Dumas Combustion via elemental analysis at three sampling dates (January, February and March) during the 2017-2018 growing season. The GreenSeeker demonstrated the greatest sensor potential to predict vine canopy N content (r²=0.92). However, its predictability potential was both cultivar and sampling time dependent, as found with the Crop Circle ACS-430 and SPAD-502 m. Alternatively, NIRS strongly predicted vine canopy N content independent of sampling time and cultivar (r²=0.94, RMSECV=0.071). This study demonstrates that lab-based NIRS has the strongest potential to be utilised as tool to predict vine canopy N status. Further research is required to assess its suitability on fresh vine leaf samples in the field to provide industry with a non-destructive alternative.