Chapter 34

Precision Viticulture

Spectral Reflectance of Grapevines and Soils

Spectral reflectance refers to the percentage of light reflected by a surface at different wavelengths. The reflectance properties of an object depend on the material and its physical and chemical state, the surface roughness, and the geometric circumstances (e.g., the incidence angle of the sunlight). The reflectance of a material also varies with the wavelength of the electromagnetic energy. These differences in reflectance make it possible to identify crops and soils by analyzing their spectral reflectance signatures. These signatures are visualized in spectral reflectance curves, which display the percentage of reflectance as a function of wavelength.

Spectral Reflectance of Grapevines

Remote and ground-based proximal sensing of vegetation is mainly performed by obtaining the electromagnetic wave reflectance information from canopies using passive sensors. It is well known that the reflectance of light spectra from plants changes with plant type, water content within tissues, and other intrinsic factors. The different components of the canopy structure can reflect energy at various wavelengths, depending on the molecules present in the tissues. The spectral bands used in precision viticulture include visible (VIS; 400–700nm), near-infrared (NIR; 700–1,000nm), shortwave infrared (SWIR; 1,000–2,500nm), and thermal infrared (TIR; 8,000–14,000 nm).

Vegetation Indices

The vegetation index (VI) is one of the most commonly used characteristic parameters in the field of crop growth monitoring. Vegetative indices are dimensionless numerical measures that provide information related to the vegetation’s activity and its interactions along the electromagnetic spectrum, such as the Normalized Difference Vegetation Index (NDVI), percent vegetation cover, chlorophyll content, and biomass, among others. The concept of a vegetation index allows the inference of specific plant properties and sources of stress. A VI uses the relationship of reflectance in two or more spectral regions combined in an equation to infer plant properties.

Spectral Reflectance of Soils

Soil spectral reflectance refers to the manner in which soils reflect sunlight at various wavelengths. Spectral reflectance analysis is one of the most widely used techniques for assessing soil properties. It involves measuring the reflectance of electromagnetic radiation across different wavelengths, typically in the visible and near-infrared regions. This enables researchers to analyze and map various soil properties, such as moisture content, organic matter, texture, and mineral composition, with high spatial resolution. It involves measuring the reflectance of electromagnetic radiation across different wavelengths, typically in the visible and near-infrared regions.

Soil Indices

Spectral soil indices are mathematical combinations (usually ratios, differences, or normalized differences) of reflectance values at specific wavelengths, designed to highlight certain soil properties. They are similar in concept to vegetation indices (like NDVI for plants), but tailored for soil features like moisture, organic matter, salinity, texture, and mineral content.

Wireless sensor networks for irrigation management offer capability of providing continuous, real-time measurements of soil water status and vine sap flow.

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