Near infrared spectroscopy as a tool for intensive mapping of vineyards soil

The wine industry has always been particularly interested in the influence of the terroir characteristics on the features of a wine. Over the past few years, a growing interest has spurred on the mechanisms by which a particular soil influences the vine’s growth, grape variety characteristics and ultimately wine quality. Near-infrared spectroscopy (NIRS) is a rapid, non-destructive, low-cost and robust analytical method for chemical and physical property determination. Its use for soil characterization, discrimination and compound determination is rapidly increasing. In this work, NIRS data were collected in two vineyards, one in the Dão Wine Region (centre of Portugal) and one in the Vinhos Verdes Wine Region (North of Portugal) previously characterized in terms of soils. Wet, dried and dried-ground soil samples collected from specific vineyard locations were scanned on a Fourier-transform near infrared spectrometer (FTLA 2000, ABB, Quebec, Canada) in diffuse reflectance mode. Spectra were analysed with chemometric tools, namely principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). Results revealed that dried, ground soil samples gave better results, but not substantially so when compared with wet or dried samples. Discriminant models showed that the NIRS method is able to discriminate the different vineyard soil types, reproducing very accurately the mapping generated by pedology methods. Variations within the same soil type (present at different locations in the vineyard) were also detected by NIRS. The NIRS technology was shown to be suitable for correlating, complementing and perhaps eventually replacing costly, time-consuming vineyard soil mapping methods.