Comparing Nitrogen Fertilization in the Vineyard versus Supplementation in the Winery on Quality of Pinot noir and Chardonnay Wines and Productivity in the Vineyard

The overall goal of this project is to understand how nitrogen fertilization in the vineyard as compared to nitrogen supplementation in the winery affects wine properties in both a red and white cultivar. To achieve this goal, we are working in 2 vineyard blocks (Pinot noir and Chardonnay) each with a history of low nitrogen status, so that nitrogen can be added in the vineyard (to boost native must YAN) and also in the winery (to boost either ammonium-N or organic-N components of native YAN). Each variety trial has 4 treatments being evaluated using 4 replicates from the vineyard. The treatments are:

  • A) No N in vineyard + No N added in winery,
  • B) No N in vineyard + DAP in winery,
  • C) No N in vineyard + ORG-N in winery,
  • D) N Fertilized in vineyard.

The Pinot noir block was used for this trial beginning in 2015, but 2016 was the first year for Chardonnay. Unfortunately, the Pinot noir block was mistakenly tilled (alternate alleyways) by the vineyard crew in early April of 2016. We therefore, quickly replanted a grass cover crop in those alleyways, but the establishment was rather poor. The N fertilized treatment for both vineyards received 3 additions of 20 pounds per acre N, for a total of 60 pounds in 2016. We will likely reduce this to 40 pounds total in 2017, depending on results. The vineyard N addition in 2016 increased vine N status in both blocks, but the Chardonnay block responded faster and had a larger change than the Pinot noir block. The resulting must YAN levels were increased in N-fertilized vines by 38% in Pinot noir (from 176 to 243 NOPA YAN) and by 90% in Chardonnay (from 99 to 189 NOPA YAN). The vineyard N addition did not influence growth or yield of Pinot noir, nor growth of Chardonnay. The unfertilized treatment that was slated to receive organic N supplementation in the winery (treatment C) did have lower yield than the N-fertilized treatment in Chardonnay, but the other 2 treatments did not differ from the N-fertilized. Fruit solar exposure and vine water status were not altered by N fertilization in either variety in 2016. After winery additions to treatment B (+DAP) and C (+ORG-N), the N-fertilized and winery supplemented N treatments (B, C and D) had higher YAN than the Control (A) in Pinot noir. In Chardonnay, the + DAP (B) and N-fertilized (D) had the highest YAN, the + ORG-N (C) was lower than those 2 treatments, and the Control was lower still in YAN. The Pinot noir musts from N-fertilized vines fermented 1 day faster (significant at P < 0.05) than all other musts, even though YAN was just as high in the +DAP and +ORG-N musts. In Chardonnay, the Control musts with lowest YAN took about 2.5 more days to complete ferment than all other treatments, but this was not significant (P > 0.05). The sensory analysis of the 2016 wines will begin this summer.

Statewide Crop Load Project: A Researcher-Industry Partnership to Understand the Yield-Quality Relationship in Cool Climate Pinot noir and Chardonnay Production

The Statewide Crop Load project was conducted in 13 vineyard sites in 2016, including 12 Pinot noir vineyards and 1 Chardonnay vineyard. Results of the Pinot noir vineyards are reported here for data obtained as of this reporting and data are still pending from the Chardonnay vineyard. Yields during 2016 were down from 2014 and 2015, the highest yielding years of the project and were similar to yields obtained in 2013. Average yield across all crop thinning treatments and sites was 0.85 lb/ft in 2016 compared to the 5-year mean of 0.89 lb/ft. Heat units (GDD50) in 2016 were also lower than in 2014 and 2015, but harvest was earlier than the past four years with all harvest completed by the end of September. Fruit composition data indicates advanced ripening with total soluble solids ranging from 24.3 – 25.6° Brix for 2016. Analysis of fruit composition data across all sites in 2016 revealed that vineyard site, not crop level, led to differences in fruit composition. Treatment effects were tested within each vineyard site, and results show that the majority of sites (82%) had some treatment effect on fruit composition; however, the effects varied by site. No one fruit composition parameter was affected by crop level at all sites, and the most common differences found by treatment were for pH, titratable adidity, tartaric acid, and tannin in 2016. However, this effect was found at approximately one-third of vineyard sites. Furthermore, few crop level effects were found for anthocyanin content in 2016 while 15-28% of sites from 2013-2015 had higher anthocyanin with lower crop levels. Further data analysis of vine growth, fruit composition and wine sensory is underway. Sensory evaluation has been expanded to include new in-house wine evaluation methods that were developed in 2016 for implementation in 2017. To capture industry-collaborator observations from the study to be used to enhance data interpretation and to develop yield management metrics, survey and interview tools were developed in 2016 and will be conducted in 2017. Updates on this project will be provided in future grant reports and outreach to the industry.

Coupling Surface Renewal, The VSIM Model, Infrared Thermometry and Plant Water Stress Indicators to Optimize Water Application in Vineyards

Grape growers are in need of improved precision irrigation management tools that are cost effective and low labor intensive to manage both irrigation amount and timing of their crops. Multiple experiments were carried out to find alternative methods to measure grape water stress that could be couple with water use estimates obtained from surface renewal stations. These methods ranged from using single point IRT temperature measurements to fully automated station that measured surface temperature in real time. The primary objective of this year’s experiments was to determine if stress indices derived from less labor intensive methods such using VSIM and IRT models could be used as a replacement to the more costly and labor intensive commonly used by growers at this time.

Experiments were carried out in three locations. Ten surface renewal stations measured grape water use and water stress in J. Lohr vineyards located in Paso Robles. Leaf water potential measurements were made along with single point IRT canopy temperature measurements using a handheld IRT sensor. Stress indices derived from the handheld IRT temperature values had inconsistent degrees of relationship strength from one site to the next, when compared to leaf water potential values. There was no single stress index, IRT or surface renewal derived, that performed consistently better than the others across all sites. Two stationary stations measured continuous canopy temperature measurements on J. Lohr sites 11-2 and 1-2. Micrometeorological data was collected from reference evapotranspiration stations set up nearby. Stress indices derived from these two stations had strong relationships with the leaf water potential values that were measured.

Two more stationary stations making continual IRT surface temperature measurements were set up in collaboration with Terlato Wine Group over vineyards in the Napa and Pope valleys. Micrometeorological data collected from nearby weather stations were used along with the IRT surface temperatures to calculate stress indices. These stress indices had strong relationships with leaf water potential measurements.

A weather station was set up in the UC Davis Tyree teaching vineyard equipped with sensors to measure canopy temperature, windspeed, air temperature, incoming solar radiation, and relative humidity. Sensible heat flux values calculated using IRT surface temperatures and the surface renewal method had a strong relationship with sensible heat flux values calculated from eddy covariance. Canopy stomatal conductance calculated using IRT canopy temperature measurements had a strong relationship with leaf stomatal conductance values measured with a porometer and stress indices also showed high correlation with leaf water potential measurements made on the Cabernet grape vines.

Comparing Nitrogen Fertilization in the Vineyard versus Supplementation in the Winery on Quality of Pinot noir and Chardonnay Wines and Productivity in the Vineyard

The overall goal of this project is to understand how nitrogen fertilization in the vineyard as compared to nitrogen supplementation in the winery affects wine properties in both a red and white cultivar. To achieve this goal, we are working in 2 vineyard blocks (Pinot noir and Chardonnay) each with a history of low nitrogen status, so that nitrogen can be added in the vineyard (to boost native must YAN) and also in the winery (to boost either ammonium-N or organic-N components of native YAN). Each variety trial has 4 treatments being evaluated using 4 replicates from the vineyard. The treatments are:

  • A) No N in vineyard + No N added in winery
  • B) No N in vineyard + DAP in winery
  • C) No N in vineyard + ORG-N in winery
  • D) N Fertilized in vineyard.

The Pinot noir block was used for this trial beginning in 2015, but 2016 was the first year for Chardonnay. Unfortunately, the Pinot noir block was mistakenly tilled (alternate alleyways) by the vineyard crew in early April of 2016. We therefore, quickly replanted a grass cover crop in those alleyways, but the establishment was rather poor. The N fertilized treatment for both vineyards received 3 additions of 20 pounds per acre N, for a total of 60 pounds in 2016. We will likely reduce this to 40 pounds total in 2017, depending on results. The vineyard N addition in 2016 increased vine N status in both blocks, but the Chardonnay block responded faster and had a larger change than the Pinot noir block. The resulting must YAN levels were increased in N-fertilized vines by 38%in Pinot noir (from 176 to 243 NOPA YAN) and by 90%in Chardonnay (from 99 to 189 NOPA YAN). The vineyard N addition did not influence growth or yield of Pinot noir, nor growth of Chardonnay. The unfertilized treatment that was slated to receive organic N supplementation in the winery (treatment C) did have lower yield than the N-fertilized treatment in Chardonnay, but the other 2 treatments did not differ from the N-fertilized. Fruit solar exposure and vine water status were not altered by N fertilization in either variety in 2016. After winery additions to treatment B (+DAP) and C (+ORG-N), the N-fertilized and winery supplemented N treatments (B, C and D) had higher YAN than the Control (A) in Pinot noir. In Chardonnay, the + DAP (B) and N-fertilized (D) had the highest YAN, the + ORG-N (C) was lower than those 2 treatments, and the Control was lower still in YAN. The Pinot noir musts from N-fertilized vines fermented 1 day faster (significant at P < 0.05) than all other musts, even though YAN was just as high in the +DAP and +ORG-N musts. In Chardonnay, the Control musts with lowest YAN took about 2.5 more days to complete ferment than all other treatments, but this was not significant (P > 0.05). The sensory analysis of the 2016 wines will begin this summer.

An Integrated Approach to Understanding How Grapevine Root Systems Respond To and Recover From Drought Stress

With our first year of funding from CGRIC, we made significant progress on this project and exciting new discoveries about grapevine fine root responses to drought that shed light on the differences among genotypes/rootstocks. The start date of the project was delayed by ~12months while we waited for the funds to become available, thus we couldn’t justify submitting a renewal in January 2016 for additional funds. We are now submitting a renewal to continue these efforts, which will cover the costs for the second year of the project. Our labs are continuing to work together closely on this and other related projects. In addition to the experimental results described below, we have collected and begun analyzing suberin responses using flurol yellow staining for the following 16 rootstocks/genotypes from a drought experiment run by Dr. Kevin Fort (Walker Lab)

Evaluation of New Winegrape Varieties for the San Joaquin Valley

Fifty six different red and white wine grape selections are being evaluated at the Kearney Agricultural Center, in Parlier, CA. These varieties were originally selected because they originate from warm-climate Mediterranean regions, and/or were believed to have traits that would be desirable in a warm climate wine region, like the San Joaquin Valley. Most of the selections tested were relatively recently released to the industry from Foundation Plant Services and had not been previously evaluated in California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned, leaving 8 to 10 two-bud spurs per meter of cordon. However, beginning in 2013, certain varieties have also been subjected to simulated mechanical pruning. Grapes were harvested according sugar accumulation, with the harvest target for white varieties at 22° Brix, and reds at 25° Brix. A few select varieties were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic juice chemistry were determined for all 56 varieties. As was typical in the region for 2015 and similar to 2014, the early ripening varieties were harvested earlier than in previous years. The first harvest occurred on 28 July 2015, and included Erbaluce, Petit Manseng, and Picolit. Fiano, typically the earliest variety harvested, followed soon after on 30 July 2015. Having failed to meet the desired Brix threshold for harvest, hand-pruned Parellada, Vernaccia Nera, and Counoise, and mechanically pruned Counoise, Caladoc, and Corvina Veronese, were harvested at the end of the season in early November. Total yields (inclusive of rot) ranged from 5.53 kg/vine (Carmenere) to 26.75 kg/vine (hand pruned Counoise). For the simulated mechanical pruning selections, yields were generally similar or greater than their hand pruned counterparts, with the exception of Counoise. Mechanical pruning either did not affect or reduced rot incidence for varieties harvested before October. But for the late ripening varieties, the late harvest required, probably due to overcropping in the mechanically pruned treatment, increased rot incidence in Corvina Veronese and Caladoc. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Twelve varieties which performed very poorly in the first two years of the trial were topworked to new selections in 2014 and used to make wine in 2015. From the work done in previous years, the most promising varieties were identified and, combined with the newly grafted varieties, a total of 23 selections were made into wine at Constellation Brand’s experimental winery and the finished wines will be evaluated and presented in the coming year. A selection of varieties that have been consistently poor performers with regards to rot and late ripening have been identified and are good candidates to be grafted over into more-promising selections in the future of this variety trial.

Mitigation of Vineyard Greenhouse Gas Production Using Organic Floor Management Approaches

This project represents an overarching effort to develop accurate metrics for vineyard carbon footprints under two widely used organic treatments. The project coordinates with efforts by Dr. William Salas (Applied Geosolutions LLC) and Alison Jordan of the Wine Institute to calibrate the DeNitrification DeComposition model (DNDC). The model will be embedded into decision support systems (DSS) providing trending analyses for use by practitioners for carbon and energy assessments (https://metrics.sustainablewinegrowing.org/). The modeling exercises will allow us to test multiple management practices in order to lessen (mitigate) N2O emissions from California vineyards. The data is being made available to Dr. Alissa Kendall and Sonja Brodt of the Department of Agricultural and Environmental Engineering and Agricultural Sustainability Institute to assemble life cycle analyses for carbon footprints of vineyards. In this report we outline mechanistic studies undertaken to understand microbial processes and therefore better calibrate the DNDC model.

Determine The Impact of Cluster Thinning and Cluster Zone Leaf Removal on the Hormone Content of Pinot Noir Grape Berry

During the past six months we have succeeded to reproduce the flower-to-berry monitoring procedure developed in our lab with similar outcomes. The justification of this procedure is to mitigate the extreme variability of flowering events in a cluster that is assumed to explain the berry variability. Using this procedure, we were able to distinguish “early” berries (emerging from early flowering events) from “late” berries (emerging from late flowering events). Previous observations in our group suggested that flowering time was not the major contributing factor of the ripeness variability at mid- véraison stage (50%of berries are green and 50%are colored) . This was confirmed again this year via the monitoring of several phenological parameters on “early” and “late” berries. We also confirmed that the seed weight relative to seed weight better explained the ripeness of individual berries at mid-véraison stage regardless of whether berries were categorized in the early or late berry groups. Interestingly, by monitoring berry size and berry weight, we also found that “early” and “late” berries rapidly overlapped their growing curves during the early stages of the growing season (week 3 to week 6 after bloom), which suggests a developmental mechanism to mitigate developmental variability among berries of a cluster.

On the other hand, ripeness variability at véraison was not associated with berries being “early” or “late” as both berry groups had a wide range of ripeness level at mid-véraison stage (sugar and pigment content). We also validated the effects of two viticulture practices (cluster thinned and fruit-zone leaf removal) on sugar and pigment contents regardless of whether berries were “early” or “late”. In vines with clusters thinned at 0.5/shoot, both accumulation of sugar and pigment contents were significantly higher in berries during the late stages of the ripening. For the fruit-zone leaf removed, only pigment content was significantly increased in sun-exposed clusters during weeks 12-15. The fine screening we performed to mitigate the developmental variability of berries has been successfully conducted and we are in the second phase of the project this year, which is the quantification of hormone and metabolite in control, cluster thinned, and fruit-zone leaf removed grapevines.

Evaluation of New Winegrape Varieties for the San Joaquin Valley

Fifty six different red and white wine grape selections originating from warm-climate Mediterranean regions, and/or believed to have traits that would be desirable in a warm climate wine region, are being evaluated at the Kearney Agricultural Center, in Parlier, CA. Most of the selections tested were recently released to the industry from Foundation Plant Services, so certified selections have not previously been evaluated in California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon. However, beginning in 2013, certain varieties have also been subjected to simulated machine pruning. In general, we attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, but certain selections were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic chemistry were determined and wine lots were made from some selections at Constellation Brand’s experimental winery. Many varieties were harvested earlier in 2014 than they were in previous years. Fiano, a white variety, has typically been the earliest variety harvested (early August), but several other early whites and a red variety were also harvested on 11 August 2014, the same day as Fiano. About a half dozen red and white varieties failed to meet their target soluble solids level even though the last harvests occurred in early November. Yields ranged from less than 4 kg per vine for Prieto Picudo to about 30 kg of fruit per vine from the machine-pruned Counoise, a red variety. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Wines from the trial will be made available for tasting and analysis in 2015, as they have been in most of the past several years. Twelve varieties which performed very poorly in the first two years of the trial were topworked to new selections in 2014, with full crops expected in 2015. Some varieties were subjected to simulated machine pruning to determine if yield and rot problems could be ameliorated. In most cases, machine pruning substantially reduced rot and increased yields, but the higher yield severely delayed ripening of some varieties and, in Falanghina, was associated with slightly higher levels of rot.

Evaluation of Grapevine Rootstock Selections

A team of academic, government, and industry partners developed a plan for evaluating nearly 700 rootstock selections from a USDA-ARS rootstock breeding program. All the vines were assessed for desirable traits, including the production of abundant, well-matured canes of adequate diameter, length, and internode spacing, with minimal lateral shoot growth, powdery mildew scars, freeze damage, or fruit production. Based on these criteria, 240 vines having very poor traits were identified and discarded, and 30 selections with very good traits were prioritized for further evaluation. Cuttings from the high-priority selections were distributed to several academic and industry labs, where their rooting ability, nematode resistance, and virus status were tested. These tests narrowed the high priority list to six virus-free stocks which were resistant to aggressive strains of root-knot nematodes (RKNs). Some of the six high-priority vines rooted poorly in one or both cooperator’s labs. Weak rooting is unacceptable, and may confound nematode resistance testing, so we propose to retest these selections, using more cuttings, and benefitting from the expertise of a commercial grapevine nursery. Most of the remaining selections were eliminated because they were found to be susceptible to RKN by one or both labs, or they rooted poorly in both labs. One RKN-resistant selection rooted very well but tested positive for SyV-1 and RSP viruses, so it will be forwarded to Foundation Plant Services for virus elimination; testing on this selection will resume after clean plant material becomes available. Four additional rootstock selections were added to the high priority list based on the performance of Syrah when grafted to those stocks. Cuttings from those four selections will be distributed to the cooperators for advanced testing.