CE Specialist Kurtural's Research in Applied Viticulture

Kaan Kurtural

CE Specialist Kurtural explains his research: 

Viticulture is evolving and the way growers have responded to legislative and economic changes has paved the way for our laboratory. One research area where we have made progress is in mechanical vineyard management and paving the way for variable rate management in vineyards using sensing and applying precision viticulture methods. In collaboration with growers and original equipment manufacturers we have made improvements to existing mechanical pruning machinery. Previously growers could only pre-prune vineyards then would return to finish pruning manually to adjust final bud numbers. Our work concluded that pruning can be achieved mechanically in a number of trellising systems with one pass, reducing costs from $403.59/acre to $81.54/acre. However, pruning is a rough regulator of yield. Growers may apply shoot thinning, cluster thinning or leaf removal to balance the grapevine to the capacity of a given site. Almost all of these practices were applied manually in the past. Our work with original equipment manufacturers and growers concluded that both in upright and downward growth habit grapevines these practices can be achieved mechanically with no deleterious effects on berry composition. However, since most of these practices would affect exposed leaf area, applied water amounts for these ameliorated practices needed attention. For example, Merlot grapevines when grown using conventional methods would require 2.72 megaliters of water applied per Hectare and would only produce about 1100 grams of total anthocyanins per hectare. Conversely, Merlot grapevines when grown with pre-bloom mechanical leaf removal (where 20% of the exposed leaf area removed) required only 2.32 megaliters of water per applied per Hectare producing 1755 grams of total anthocyanins per hectare resulting in water savings and a better intermediate end product that was delivered to the crush pad. 

These approaches are currently being applied uniformly across vineyards without any regard for variation in planting systems. Although growers and vintners are aware that variation in vineyards exist, few tools are available to take corrective action. For example, the lack of on-the-go sensors that deliver grower-interpretable results for vineyards has been limiting. In collaboration with Cornell University, Carnegie Mellon University and Newcastle University we initiated a long-term project across California and state of New York. In this work we are investigating taking corrective actions in vineyards with the aim of commercializing variable rate management in table and wine grape vineyards. Specifically we are studying the contributions of soil resistivity, early season canopy reflectance and crop level to vineyard variability to delineate a spatial decision support system in vineyards. Prior to the initiation of this project there were very few sensors available that could be used in vineyards. In collaboration with our research partners, existing sensors are being adapted for vineyard use. Furthermore, a new sensor has also been developed by our research partner at Carnegie Mellon University to estimate yield in vineyards. The combined output of these sensors is a spatially explicit map that is divided into management zones. Corrective actions that maybe taken are: applied water amounts, shoot removal, leaf removal, berry thinning, and soil amendment additions or cover crop removal at a variable rate to deliver uniform mass and berry composition. This project, as mentioned above, is a coordinated effort between universities as well as grower organizations such as the National Grape and Wine Initiative and individual producers. 

Few grape growing regions in California have been exempt from the State's prolonged drought. Growers in the North Coast regions have started seeing raisining, berry collapse or greater astringency than customarily witnessed in their high value vineyards. To provide practical solutions, as well as to investigate fundamental processes that contribute anecdotal evidence presented by growers, we initiated a project in collaboration with Dr. Dario Cantu's laboratory at UC Davis and a grape grower organization, at our Oakville Station laboratory. We installed five different colored shade nets that cover the fruiting zone that may affect the wavelength of irradiance (for controls, we left the grapevine uncovered). Those covered vines were then crossed with two applied water amounts. We have seen that colored shade nets do not provide any greater shading than a sprawling canopy that is uncovered. However, they do change the berry temperature and the wavelengths that are subtending the berries. Therefore, as applied water amounts change, the berry size thus cluster architecture, as well as berry skin mass, are altered. We are looking forward to processing the temporal berry samples for gene expression data and flavonoid composition. 

In addition to the large scale projects (described above) we have initiated projects at the Oakville Station as well as on campus for mission-oriented research. At the Oakville Station, a new vineyard was planted in collaboration with Dr. Dave Smart to test five new trellising systems against the ubiquitous vertically shoot positioned system and how these systems may be best mechanized given the current economic climate. Furthermore, nitrogen, potassium and water use efficiency of these systems are unknown and are going to be studied. A new mono-cultivar block was planted to test, train and develop sensor based, single-vine resolution precision vineyard management. A rootstock and clonal trial was also established at Oakville Station to investigate which clones maybe more adaptable to mechanical management for Cabernet Sauvignon and Malbec. In the UC Davis Campus vineyard (in collaboration with Drs. Andrew Walker and Andrew McElrone) a trial was established to investigate the root biology of seven rootstock genotypes under five different irrigation regimes using geomatics. 

Research results that are not communicated to stakeholders are not very useful. In an effort to keep our stakeholders abreast of new findings we plan to host and/or participate in the following events: 

RAVE - December 9: 
a) Assessing variability in the vineyard through a spatially explicit selective-harvest approach: A case study in Sonoma 
b) Mitigating Light and Temperature Environment of Red Wine Grape with Color Shade Nets 
c) Water productivity and flavonoid composition of Merlot is Ameliorated by Mechanical Management 
d) Proanthocyanidin Compositional Shifts in Grape Berry Skin are Modulated by Canopy Gaps and Applied Water Amounts 

Napa Valley Grape Growers: Rootstock: 
a) November 8th - UC Davis Department of Viticulture & Enology/Oakville Station Booth 

UC Davis On the Road: 
a) November 16th in Madera 

Wine Flavor 101: 
a) Crop forecasting and harvest logistics - April 20, 2017 

UC Davis Department of Viticulture & Enology Oakville Station Grape Day: 
a) Early June 2017