Grapevine nitrogen status: correlation between chlorophyll indices n-tester and spadGrapevine nitrogen status

Abstract

Context and purpose of the study – Knowledge of the nitrogen nutrition status of grapevines is essential for the sustainable management of their nutrition for the production of quality grapes. The measurement of the chlorophyll index is a rapid, non-destructive and relatively inexpensive method that provides a good approximation of the nitrogen nutrition status of the vine during the season. Interpretation thresholds are currently insufficient or non-existent for some chlorophyll meters. Ideally, they should be available for each variety and each phenological stage. In order to popularize the use of chlorophyll-meters, measurements were carried out at Agroscope in Switzerland to establish the correlation between the indices obtained by the devices N-tester and SPAD 502.

Material and methods – In 2022, 500 measurements were carried out with the two devices N-tester and SPAD 502 in parallel, at three phenological stages (flowering, veraison and post-harvest), on the two grape varieties chasselas and pinot noir. The vines were all trained in Guyot pruning. Each measurement consisted of 30 flashes of each device taken at the same locations on the main leaves of the fruit zone.

Results – Measurements from both devices showed an excellent correlation (r = 0.97; P < 0.0001) between SPAD and N-tester indices. Given the linear regression obtained (y = 0.06x + 6.25), the thresholds of the SPAD index measured on vines at veraison, for the interpretation of the nitrogen nutrition status, were calculated from the correlation with the N-tester index, whose thresholds are already known. It is not recommended to carry out measurements at other times of the season due to the greater fluctuation of the data due to the age of the leaves, the water status of the vine or the possible presence of disease symptoms (e.g., mildew, powdery mildew) or other deficiencies (e.g., iron, magnesium). These results allow scientists and growers to easily estimate the nitrogen status of the vine at veraison in the vineyard and, if necessary, to compare/convert the results of the two devices.