The evaluation of an optical method to estimate leaf area of grapevines

Abstract

The ability of LAI 2000 Plant Canopy Analyzer to estimate the leaf area index (LAI) of grapevines canopies accurately was evaluated. This indirectly estimated LAI of grapevine canopies was compared to the directly measured (observed) LAI, using fully developed V. labrusca L. cultivar, 'Concord', canopies in 1993; In 1994, 'Concord' and 'Chardonnay' canopies at different growing stages were similarly analyzed. Calibration was required to obtain reliable estimates of LAI because the growth habit of grapevines did not satisfy the requirement for random foliage distribution when applying gap fraction analysis. The most improtant consideration was sensor view field, which should be maximized when viewing randomly distributed canopies. Variables tested included reading postition, reading direction, view zenith angle and view opening angle. It was easier to apply gap fraction analysis with a vigorous cultivar, 'Concord' because of its large canopy and more random foliage distribution than with 'Chardonnay'. For the latter, a typical V. vinifera grapevine, the view field needed to be narrowed because of its low vigor, pruning and training system, and non-random leaf distribution. Estimating leaf area in the middle or late season was easier than in early season when gaps between rows were large and foliage distribution was highly variable.