Vegetation index cartography as a methodology complement to terroir zoning for use in precision viticulture

Abstract

Aim: Precision Viticulture (PV) is a form of vineyard management based on tools that offer winegrowers georeferenced information of each vineyard, mainly sector mapping (sub-areas) differentiated by characteristics capable of influencing vineyard usage. This provides knowledge of the variations in these sectors and PV treats each one of them in an independent and optimised manner. This allows, amongst many other possibilities, to monitor fruit ripening with the objective of performing site-specific harvest based on the characteristics of each given sector. Local variations in soil features and natural environmental factors, such as climate, lithology, geomorphology and soil, determine the units that drive or limit PV. Methods and results: In this paper, multispectral images are used. These have been obtained between veraison and harvest in three different years in order to calculate four vegetation indexes (VI) that have been used since the end of the last century to delimit homogenous sectors in vineyards: the Normalized Difference Vegetation Index (NDVI), the Improved Soil Adjusted Vegetation Index (MSAVI), the Simple Ratio Index (SR) and the Modified Simple Ratio Index (MSR). Mapping of these VI has allowed to relate their distribution with natural environmental factors with the objective of valuing their use in the discrimination of homogenous sectors as a complement and/or alternative to traditional methodologies to terroir zoning. Results show that, in the area studied, the vineyards planted in alluvial soil and conglomerated zones, over dominant fine-loamy, mixed, mesic, Calcixerollic Xerochrept soil series, at elevations between 519 and 604 m, oriented east and on slopes less than 5° present higher values for all four indexes throughout the three years of study. Conclusions: It is precisely these environmental elements (lithology, soil, elevation, orientation and slope) and many soil features that must be relatively uniform in order to make an efficient use of the studied VI. Significance and impact of the study: The study addresses the use of VI as a companion tool to viticultural zoning, which has not been much explored at such scale level. In addition, the results obtained may lead to changes in the use of VI, which are usually used without taking into account soil and/or terrain features.