Relation of Ground-Sensor Canopy Reflectance to Biomass Production and Grape Color in Two Merlot Vineyards

Abstract

Recent studies with optical remote sensing have demonstrated the relationship between canopy reflectance, biomass production, and certain quality attributes of grapes in red winegrape vineyards. Multispectral reflectance data are currently delivered by airborne platforms, but may not be available to producers in time to implement critical management decisions. Ground-based sensors are designed to overcome many limitations associated with satellite- or aircraft-based sensing systems. This study provides information about the potential of ground-based canopy sensors in predicting biomass production and quality attributes of grapes in two Merlot vineyards. Multispectral sensors were mounted on a tractor and recorded canopy reflectance from two different viewing angles and fields of view along selected rows of vines. The normalized difference vegetation index (NDVI) was compared to pruning weight, phenol, anthocyanin, and sugar content of grapes measured in 25 to 32 sampling positions within each vineyard over two growing seasons. Sensor canopy reflectance predicted the spatial variation of biomass production in the two vineyards with varying degrees of precision. A nadir viewing angle of the canopy near veraison provided estimates of NDVI that were better predictors of biomass production, while masking the sensor optics provided more reliable estimates of canopy reflectance. The quadratic relationship between NDVI and pruning weight improved with decreasing sensor resolution (from one plant to four plants). A negative correlation between canopy reflectance and anthocyanin content of grapes was significant in one of the two vineyards and implied an inverse relationship between biomass production and grape color. Results demonstrate the potential value of proximal remote sensing in optimizing production, improving wine quality, and reducing chemical inputs.