Quantifying spatio-temporal variation of leaf chlorophyll and nitrogen contents in vineyards

Abstract

Precision viticulture requires the characterisation of the spatio-temporal variability of the vineyard status to design the appropriate management for each area. The goal of this work was to characterise the spatio-temporal variability of leaf chlorophyll (Chl) and nitrogen (N) content and their relationship with the vegetative growth in a three ha commercial vineyard (Vitis vinifera L.) using a geostatistical approach. Leaf Chl and N contents were assessed by two fluorescence indices provided by a hand-held fluorescence sensor. Fluorescence measurements were taken along five dates, from veraison to harvest, on 72 sampling points delineated on a regular grid across the vineyard. Shoot pruning weight (SPW) was measured for each sampling point as indicator of the grapevine vegetative growth. Geostatistical analysis was applied to model the spatial variability of leaf Chl and N content and SPW. The spread showed an increase of the variability of leaf Chl and N content during the ripening period, reaching maximum values prior to harvest. The variograms illustrated a similarity of the spatial variability structure of leaf Chl at all timings, unlike N which showed changing spatial variability structures along the ripening period. The Kappa index evidenced a slight intra-season stability for both Chl and N and showed that N could not be used alone as an indicator to delineate vigour management areas. The existence of spatio-temporal variability of key vegetative components was proved and its knowledge is crucial to implement precision viticulture approach such as variable rate application of fertilizers or water as needed.