Non-destructive zoning of winegrape technological maturity using a fluorescence optical sensor

Abstract

Non-destructive mapping of the Chlorophyll (Chl) index, inversely correlated to the technological maturity, was carried out at ‘La Corsa’ winery (South Tuscany, Italy) on 5^th September 2014, just before harvest, on grape bunches of Sangiovese cv. using a fluorescence optical sensor. Optical measurements were performed manually on a 5.5 ha vineyard using a 15m x 15m grid, detecting for each point six bunches from three adjacent vines on two contiguous rows. The grape soluble solids concentration (SSC) based on a Chl index calibration ranged between 18.0 and 23.2 °Bx. Its spatial heterogeneity was reported in a colorimetric map divided into two areas with lower and higher SSC by segmentation based on the median (21.6 °Bx). Destructive analysis of grape samplings confirmed a difference in SSC between the two selected areas, in accordance with the non-destructive estimate. On the same day of grape bunches measurements, mapping of the NDVI index was determined on vine leaves using a portable reflectance sensor mounted on a quad. In most of the parts of the map, the expected negative correlation between the vigor-NDVI map and the sugar- Chl map was observed. However, in some specific areas high vine vigor was associated to high grape sugar content, likely due to a soil and/or clone influence. The aim of the work was to evaluate the advantages of a fluorescence optical sensor in precision viticulture to select winegrape with different technological maturity. These data integrate those on the phenolic maturity that can be provided by the same device, in order to have as perspectives a more complete information on grape quality.