ESTIMATION OF GRAPEVINE CROP MASS AND YIELD VIA AUTOMATED MEASUREMENTS OF TRELLIS TENSION

A novel approach was devised to estimate vegetative growth and fruit mass (i.e., yield) in grapevines by continuously measuring the tension in the horizontal (cordon) support wire of the trellis. Load cells installed in-line with the cordon wire were connected to an automated data acquisition system, a major departure from the viticulture industry’s standard method of collecting fruit samples by hand two or three times per growing season. Each experimental row in the vineyard was calibrated to determine the change in tension in that row in response to an increase in known mass on the cordon wire. The effects of temperature on wire tension were removed by post-processing with a regression-based empirical protocol, which corrected the raw data to a standard temperature. Because data were averaged over 15 min, wind gusts appeared to have little measurable effect on the tension measurement. A smoothing algorithm removed remaining transient disturbances in the data without masking significant events like crop thinning or harvest. Results to date suggest a linear relationship between wire tension and fruit mass that varies among rows, but not within a row, during a single season. Yields were between 4.5 and 20.2 t ha-1 (2 to 9 t acre-1).