|Pierce, Francis - WSU|
Submitted to: American Journal of Enology and Viticulture
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2003
Publication Date: October 15, 2003
Citation: TARARA, J.M., FERGUSON, J.C., BLOM, P.E., PIERCE, F.J. A NOVEL METHOD OF AUTOMATING THE ESTIMATION OF GRAPEVINE YIELDS. AMERICAN JOURNAL OF ENOLOGY AND VITICULTURE. 2003. Technical Abstract: A novel approach was devised to make continuous estimates of growth and yield in grapevines by measuring tension in the horizontal (cordon) support wire of the trellis. Load cells were installed in-line with the cordon wire and connected to an automated data acquisition system, a major departure from the grape industry's standard method of collecting fruit samples by hand two or three times per growing season. The tension change in the wire between budburst and harvest was used to estimate vegetative growth and total fruit mass (i.e., yield). Each experimental row was calibrated with known mass to determine the tension response in that row to an increase in mass on the cordon wire. The effects of temperature on tension in the wire were removed by post-processing with a regression-based empirical protocol, which corrected the raw data to a standard temperature. Because the data were averaged over 15 min, wind gusts appeared to have no measurable effect on the tension measurement. A smoothing algorithm removed remaining transient disturbances in the data without masking significant changes in tension, 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. Responses of the load cells to increases in mass on the trellis were similar at various yields ranging from 4.5 to 20.2 t/ha. The sensitivity of the load cell to changes in crop mass declines exponentially with distance from the sensor. For well-watered vines whose canopies grow all season, one must separate vegetative mass from fruit mass to resolve the proportion of the wire tension that is due to fruit, the harvested component.