Author(s):
Lee Johnson* - California State University, Monterey Bay
Abstract:
Vineyard irrigation and resulting water status affect several key cropping aspects including ripening rate, infestation/disease susceptibility, fruit composition, and yield. California winegrowers are making increased use of airborne normalized difference vegetation index (NDVI) imagery, formed from red and near-infrared spectral bands, for various management decisions. This study demonstrated the potential use of such imagery for evaluating crop evapotranspiration (ET) and resulting irrigation demand. The NDVI, which is highly sensitive to vegetation vigor, was correlated with ground-based measurements of noontime shaded-area for vertically-trained canopies differing in maturity, cultivar, and row spacing (r=0.79). The NDVI imagery was transformed according to the observed relationship and used to map shaded-area throughout a large commercial vineyard in California's Napa Valley. Ground measurements of shaded-area near solar noon, in turn, were strongly related to the ET crop-coefficient (r=0.97). The study results thus suggest the possibility of using optical remote sensing to map vineyard crop coefficients. When combined with reference ET data and appropriate crop water-balance models, irrigation demand may be efficiently derived and mapped
