THE EVALUATION OF AN OPTICAL METHOD TO ESTIMATE LEAF-AREA OF GRAPEVINES

The ability of LAI 2000 Plant Canopy Analyzer to estimate the leaf are a index (LAI) of grapevines canopies accurately was evaluated. This in directly estimated LAI of grapevine canopies was compared to the direc tly measured (observed) LAI, using fully developed V. labrusca L. cult ivar, 'Concord', canopies in 1993; In 1994,'Concord' and 'Chardonnay' canopies at different growing stages were similarly analyzed. Calibrat ion was required to obtain reliable estimates of LAI because the growt h habit of grapevines did not satisfy the requirement for random folia ge distribution when applying gap fraction analysis. The most improtan t consideration was sensor view field, which should be maximized when viewing randomly distributed canopies. Variables tested included readi ng postition, reading direction, view zenith angle and view opening an gle. It was easier to apply gap fraction analysis with a vigorous cult ivar, 'Concord', because of its large canopy and more random foliage d istribution than with 'Chardonnay'. For the latter, a typical V. vinif era 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 distributio n was highly variable.