Submitted to: Fruit, Nut, and Vegetable Production Engineering International Symposium
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2005
Publication Date: 9/16/2005
Citation: Tarara, J.M., Blom, P.E., Ferguson, J.C., Pierce, F.J. 2005. Estimating grapevine yield from measurements of trellis wire tension. In: Proceedings of the 7th International Fruit, Nut, and Vegetable Production Engineering Symposium, September 12-16, 2005, Montpellier, France. 2005. CDROM. Interpretive Summary: Automated estimation of yield in grapes and other trellised crops could increase labor and production efficiencies by providing real-time (continuous) data, giving farmers and wineries more detailed information for crop management. We have been developing a novel approach to estimate yields in vineyards that exploits the fact that farmers support grapevines with trellises. Although trellis designs vary, they share common features like evenly spaced support posts and at least one horizontal support wire strung from post to post. In engineering terms, a trellised crop like grapevines is a load exerting tension on the support wire. The load consists of the weight of fruit, leaves, shoots, trunk, and the wire itself. One can measure the tension in the trellis wire and relate it to the weight of the load, thus ultimately to yield. Our early experiments showed that there is a linear relationship between wire tension and weight on the wire, and that this relationship is constant during a single season, which suggested that this new technique might be feasible in commercial vineyards. Our demonstration in a research vineyard was promising enough to warrant an application for a patent in 2003. Now in both research and commercial vineyards, we continue to sort out some practical obstacles, specifically: 1) how many vineyard rows to measure, 2) where is the best position along the row to measure wire tension, 3) whether the technique will work in multiple-wire trellises, and 4) how to adjust for the weight of the vine canopy in well-watered vineyards where the canopy may gain weight concurrently with the fruit.
Technical Abstract: A novel approach was devised to estimate vegetative growth and fruit mass (i.e., yield) in grapevines by continuously measuring tension in the horizontal (cordon) wire of the trellis. Hand collection, counting, and weighing of fruit clusters remains the standard approach to yield estimation in vineyards. Automating this process may facilitate continuous crop monitoring and significant savings in labor. Physical support of grapevines by a trellis provides a unique opportunity to correlate a measurement of tension in the trellis wire with fruit mass and yield. A single-wire trellis in a 0.34-ha research vineyard was retrofitted to minimize friction points and movement by end posts. Load cells were installed in-line with the cordon wire near the end post, and each row was calibrated with known mass. Load cell output and wire temperature were measured continuously from budburst through leaf fall. Harvest occurred in three increments; yield per vine was recorded. There was a linear relationship between known mass hung on the wire and wire tension. The effects of wire temperature on wire tension were accounted for by post-processing. The averaging period of the datalogger was sufficient to render the effects of wind on wire tension below the measurement threshold. Results to date suggest a linear relationship between wire tension and fruit mass that varies by vineyard row, but not within a row during a single season. The 12 tension-based yield estimates were within 15% of the corresponding harvested mass of fruit. Follow-on work during the most recent growing season suggests that isolating a defined length of trellis will facilitate the setting of more uniform initial tensions, improve the sensitivity of the system, and may mitigate some of the effects of environmental transients on the load cell signal.