Abstract
<p style="text-align: justify;"><strong>Aims:</strong> Yield monitors are becoming more common in North America. This research evaluates the precision and accuracy of a retro-fitted, commercially available grape yield monitor mid-season, for crop estimation and crop thinning applications, and at harvest for yield mapping.</p><p style="text-align: justify;"><strong>Methods and Results:</strong> Several grape yield monitors were mounted on the discharge conveyor belt of grape harvesters in both commercial and research vineyards in North America. Sensor response was compared to manual measurements at multiple masses, ranging from 20 kg to 28 Mg over the course of three seasons. Measurements were taken during crop thinning and estimation (mid-season) and at harvest. Results showed that the grape yield monitor performance was sufficient to generate good spatial maps of the relative variation in harvest yield and mid-season thinned yield. However, at harvest the sensor showed a shift in response between days of up to ±15%, such that the generation of absolute yield maps required a daily calibration against a known mass. Within a day (single harvest operation) the sensor response did not appear to drift. Mid-season applications required a different calibration to harvest applications.</p><p style="text-align: justify;"><strong>Conclusion:</strong> The yield sensor worked well for both mid-season and at harvest operations in North American vineyards but required a daily calibration to avoid drift issues. The mid-season yield calibrations were different between seasons; however, the harvest calibration factor was stable between seasons.</p><strong>Significance and Impact of study:</strong> The study showed that a commercial yield monitor with correct calibration was effective at even low fruit flow. This opens the possibility of using a harvest sensor mid-season to mechanically estimate fruit load from small point samples and to map the amount of fruit removed during fruit thinning operations. This will improve the quality of information available to viticulturist to understand fruit and crop load. The commercial yield monitor is suitable for use in North American vineyards.
Highlights
On-harvester grape yield monitors have been commercially available since the late 1990s
7 grape yield monitor (GYM) systems were used within this study : 5 systems were installed on commercial harvesters that operated primarily in winegrape vineyards in the San Joachin valley in California, 1 GYM system was installed on a commercial harvester in the Lake Erie region, NY State and 1 GYM system was installed on a harvester associated with the Cornell Lake Erie Research and Extension Laboraty (CLEREL) juicegrape vineyards in the Lake Erie viticulture area in NY State
Truck-scale measurements : Figure 1 shows the relationship between the GYM readings and the mass of weighed grapes for truck-scale data collected at harvest in both California and NY State
Summary
On-harvester grape yield monitors have been commercially available since the late 1990s. The first commercially available grape yield monitor was the HM-570 grape yield monitor released by HarvestMaster (Logan, UT, USA). The HM-570 was a volumetric sensor that used ultra-sonic sensors mounted above the discharge conveyor to measure the height (volume) of grapes on the conveyor belt. Volume was calibrated to mass using a density coefficient. Considerable issues with the operation of the system in Australian conditions between 1999 and 2002 were noted by researchers at CSIRO and The University of Sydney (Taylor, 2004). The density coefficient required constant adjustment, between varieties and throughout the day as the ratio of berries to must being offloaded changed
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