Ground Truthing and Physiological Validation of Vis-NIR Spectral Indices for Early Diagnosis of Nitrogen Deficiency in cv. Barbera (Vitis vinifera L.) Grapevines

Abstract

Several narrow or broadband spectral indices can be calculated at varying spatial and spectral resolution, which can then be correlated with the physiological and nutritional status of the leaves. In a three-year trial carried out on fruiting, potted cv. Barbera grapevines subjected to full (N+) or no (N0) nitrogen supply, seasonal evolution of different leaf spectral indices were correlated with non-destructive chlorophyll readings (Minolta SPAD meter), leaf gas exchange, and vine performance. Throughout the entire trial, N starvation resulted in greater-than-proportional limitation of vine yield as compared to vegetative growth (55% compared to 26% less than values measured on N+). Indices calculated within the red-edge spectral domain had highest sensitivity to relative change between N+ and N0, also indicating that the promptest response was recorded at the median shoot zone level. Twelve broadband indices were linearly correlated with leaf blade N concentration at veraison, indicating that N values ≤ 1.8% of dry matter identify a limiting N status. Any of these indices collected at the leaf level can be reliably used as a non-destructive predictor of N availability, albeit due to significant between-year variation in their absolute values at a given N level, readings should always include a well-supplied N treatment.

Gas exchange, vine performance and modulation of secondary metabolism in Vitis vinifera L. cv Barbera following long-term nitrogen deficit

“…Small dots represent the individual logFC for each metabolite photosynthetic rates. On a methodological basis, it is confirmed that SPAD readings and A rates might show relatively poor correlation, especially when SPAD readings are above the 25 units (Squeri et al 2019;Steele et al 2008). The most significant leaf A response observed in our study was that, across leaf position and over a total leaf age span from about 30 to 125 days, N0 maintained A rates quite similar to the N + plants.…”

“…Leaf N concentration assessed pre-veraison in N0 was decreased by 28%, to a leaf concentration of 1.66%. According to literature (Keller and Hrazdina, 1998;Paul Schreiner et al 2013;Squeri et al 2019) this value is below the warning threshold of about 1.80% that should be warranted at that phenological stage.…”

Assessing Grapevine Biophysical Parameters From Unmanned Aerial Vehicles Hyperspectral Imagery

“…Interpretation of the R 2 data reported in Table 3 vs. means, range of variation and coefficient of variation (CV) of agronomic and physiological variables is quite puzzling. In general terms, for a given index, closer correlation is expected any time a given variable, primarily due to soil heterogeneity, shows a larger degree of variability ( Trought et al, 2008 ; Baluja et al, 2013 ; Squeri et al, 2019 ; Gatti et al, 2021 ). This concept seems to hold, for instance, when RVI, NDVI3, SR680, and EVI2 are correlated with Ψ pd and Ψ md .…”

Effects of intra-vineyard variability and soil heterogeneity on vine performance, dry matter and nutrient partitioning

“…This was quite interesting as it indicated that N leaf could act as a diagnostic tool to identify vigor levels. Recent work by Squeri et al (2019) has ascertained that several broadband VIS-NIR indices can be profitably used for non-destructive estimates of N leaf concentration therefore making the procedure fast and effective.…”