Sensor technology to assess grape bunch temperature variability in Vitis vinifera L. cv. Shiraz

[摘要] ENGLISH ABSTRACT: The microclimate environment around the bunch is complex. The spatial distribution of leaves as well as bunch position and morphology impact on the path of direct radiation received by the berries. Canopy microclimate is largely determined by the meteorological conditions (air temperature, solar radiation, wind speed and direction, relative humidity, and precipitation) as well as management practices (trellis/training system, canopy height, vine spacing, row orientation, canopy management practices, irrigation and soil variability and management). The fact that the grapevine continuously responds to its environment, adds to the complexity and dynamic nature of the microclimate that the bunches experience. Field studies involving the effect of the natural bunch environment (i.e. light and temperature conditions) on berry composition, are therefore a challenge, due to the difficulties in quantifying meteorological elements such as temperature and light, which can be hugely variable.There are different sensors available to assess bunch and berry temperature and it can be deployed in different ways within the grapevine canopy, but the difficulty remains in studying the variability that exists within a bunch. This study investigated the value of available sensor technology to measure bunch/berry temperature as well as the spatial and temporal variability on a bunch. Differences in temperature on an intra-berry level were assessed whereas the impact of canopy configuration and bunch orientation on the different sensor levels was also investigated. The contribution of macro- and mesoclimate on bunch and berry temperature was addressed by measuring at two locations (Robertson and Stellenbosch). The potential long term differences in temperature within a bunch with regard to thermal accumulation are discussed. Issues around sensor placement and some technical difficulties related to the sensors are discussed.The results indicated how the effects of mesoclimate were transferred through to the different sensors. A dominating effect of the sea breeze in Stellenbosch was found. Canopy configuration/architecture affected the light regime in the canopy, consequently impacting on bunch temperature variability, specifically in Stellenbosch where a Ballerina trellising system was used. Bunch orientation resulted in differences in the temporal variability of bunch/berry temperature and little variability was observed in temperature within the berry. Temperatures of berries situated at the back of the bunch were judged more optimal compared to exposed berries. Direct radiation caused extreme temperatures in exposed berries, which may be detrimental to berry composition and wine quality. This emphasized the importance of the canopy (trellis/training system and management practices) in protecting the bunch from extreme conditions. The large on-bunch spatial variability, observed from measurements with the thermal imager, demonstrated the importance of sensor placement in quantifying the bunch temperature regime; this is also relevant for the future development of berry temperature modelling. Thermal accumulation through the season also illustrated the variability that existed within a bunch, suggesting a potential long term effect on the berry composition. This study proved, in conditions similar to those that may prevail in the South African wine industry, that sensor type and positioning need to be carefully considered in any viticultural/oenological study where bunch microclimate and grape temperatures are assessed.

[发布机构] Stellenbosch University