Assessment of the spatial variability of vegetative status in vineyards using non-destructive sensorsApplication of remote and proximal sensing technologies in precision viticulture stars

Abstract

Introduction: The vegetative status of grapevines influences yield and grape composition. The assessment of the vineyard spatial and temporal variability in precision viticulture requires a large amount of data. Traditional methods are not suitable, as they are time and labour demanding, making the analysis of a high number of samples at different timings not feasible. For this purpose, remote and proximal sensing techniques could be useful for monitoring the vineyards in a reliable, fast and non-destructive way. Objectives: The aim pursued by this research was to assess the spatial and temporal variability of the vegetative status of a vineyard using nondestructive sensors. Towards that end, the usefulness of a remotely piloted aerial system (RPAS) multispectral imagery was tested to assess the vegetative growth of a vineyard. A special focus was set on proximal sensing, especially on a fluorescence sensor used either manually and on-the-go, to determine chlorophyll, flavonol and nitrogen content in grapevine leaves. Materials and methods: A multispectral sensor mounted on a RPAS was employed for monitoring the spatial variability of the vegetative status of a commercial vineyard (Vitis vinifera L.) and the assessment of vegetative parameters, such as leaf area, shoot length and pruning weight, leaf chlorophyll content and nitrogen status. Subsequently, a fluorescence sensor, used manually and mounted on a quad, was used for assessing the leaf chlorophyll, epidermal flavonol and nitrogen content and monitoring the spatial variability of the vineyard vegetative and nutritional status. Results and discussion: The spectral indices derived from RPAS multispectral imagery yielded significant and moderate correlations with pruning weight, secondary shoot length, secondary leaf area, leaf chlorophyll content and nitrogen status. These results indicated its potential to appraise the vineyard vegetative status but also revealed some disadvantages regarding technological and operational factors. Regarding proximal sensing, the handheld fluorescence sensor demonstrated its capability to properly measure the chlorophyll, epidermal flavonols and nitrogen content in grapevine leaves. The best indicators of these vegetative and nutritional components were found to be the fluorescence indices of the whole leaf (adaxial and abaxial). Thanks to the calibration equations provided, the leaf chlorophyll concentration can be obtained from the fluorescence measurements. Concerning the nitrogen status, among all the possible equations of the nitrogen balance index (NBI), the one calculated as the chlorophyll-toflavonol ratio yielded the best evaluation of the nitrogen status of the grapevine. The hand-held fluorescence sensor allowed characterising the spatio-temporal variability of leaf chlorophyll content and nitrogen status along the ripening season. While the nitrogen status showed different spatial variability across the season, leaf chlorophyll content spatial behaviour remained stable. Moreover, the fluorescence sensor adapted to be mounted on a vehicle demonstrated its capability to reliably estimate the chlorophyll, epidermal flavonol and nitrogen content on-the-go in grapevine leaves, and to assess their spatial variability within the vineyard. Conclusions: Remote and proximal sensing have proved to be certainly useful in precision viticulture as they are able to provide a large amount of data in a fast and non-destructive way, overcoming the disadvantages of the classical manual, destructive, laborious methods. Specifically, the fluorescence sensor has shown to be a precise tool to assess xv key vegetative and nutritional parameters in the field. Furthermore, its successful adaptation to operate mounted on a vehicle and perform an onthe- go assessment of the vegetative status of the vineyard is a significant step forward in the current process of sensor integration on mobile platforms and the practical implementation of the precision viticulture techniques.