Evaluation of a commercial grape yield monitor for use mid-season and at-harvest

摘要

Aims: 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.Methods and Results: 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.Conclusion: 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.Significance and Impact of study: 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. IntroductionOn-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 then 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). In particular, the density coefficient required constant adjustment, not only between varieties but also throughout the day as the ratio of berries to must being offloaded changed.In 2001, Farmscan Ltd (Western Australia, Australia) released a load cell-based grape yield sensor that proved to be more reliable than the HarvestMaster system (Taylor 2004); however problems with Farmscan’s parent company effectively resulted in the Farmscan grape yield sensor being withdrawn from the market by 2007. A second load cell-based system was commercially released in 2005 in Australia by Advanced Technology Viticulture (ATV) (Adelaide, South Australia, Australia)? Since 2005 there has been a slow but steady increase in adoption of the ATV grape yield monitor, predominantly in Australia but increasingly in North America with 6 yield monitor installations in the USA in 2012, 9 in 2013 and >30 in 2014.Examples of yield maps have been presented in the literature (Bramley & Hamilton, 2004; Tisseyre et al., 2007; Arnó et al., 2009), as well as a geostatistical analysis of the spatial variation observed in Australian and European viticulture (Taylor et al., 2005); however, there has been no independent evaluation of this technology published. Given the increased interest in grape yield monitors in the USA, and the expected continued growth in adoption, an evaluation of the accuracy and the potential uses of this technology is considered pertinent.Materials and MethodsSystem and Installation: The only currently available commercial grape yield monitor is manufactured, installed and supported by Advanced Technology Viticulture (ATV). The ATV grape yield monitor (GYM) is designed to be retrofitted to a discharge conveyor belt and can be altered to fit most makes of grape harvesters that use a discharge conveyor. The yield sensor consists of a weigh-frame on load cells under the discharge conveyor belt of the harvester that weighs the grapes as they are being off-loaded. A belt speed sensor, a junction box and a data logger/controller in the tractor cabin complete the system. For mapping capabilities a Global Navigation Satellite System (GNSS) receiver is also required. After each installation, a static calibration of the load cells is performed by placing known dead weights on the discharge conveyor belt ove