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Lee F. Johnson and Lars L. Pierce

The performance of the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) for indirect measurement of leaf area index (LAI) was evaluated in vineyards of California's North Coast region. Twelve plots were established, representing vineyards of differing trellis, cultivar, and planting density. Mean LAI ranged from 0.5- to 2.25-m2 leaf area per m2 ground area by direct measurement (defoliation). Indirect LAI derived by a standard two-azimuth, diagonal-transect measurement protocol was significantly related to direct LAI (r2 = 0.78, P ≤ 0.001). However, the PCA underestimated direct LAI by about a factor of two. Narrowing the instrument's conical field of view from 148° to 56° increased indirect LAI by 13% to 60% in vertically trained plots, but still resulted in substantial underestimation of direct values. Use of this PCA protocol in vineyards should therefore be accompanied by direct measurement for calibration purposes.