Determining the Impacts of Dormant Pruning Methods and Nitrogen Fertilization on Pinot Noir Bud Fruitfulness and Yield

Final report for GW18-027

Project Type: Graduate Student
Funds awarded in 2018: $22,786.00
Projected End Date: 03/30/2020
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Graduate Student:
Major Professor:
Dr. Patricia Skinkis
Oregon State University
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Project Information

Summary:

Vineyard sustainability requires attention to cultural practices and the labor to implement them in order to remain economically viable. Crop yield and quality are also major determinants of economic viability and need to be evaluated in sustainable vineyard systems. Currently grape growers in Oregon are faced with narrow profit margins as the cost to produce wine grapes is high due to 1) low yields and 2) significant manual labor required to implement cultural practices in the small family vineyards in the state. We explored vineyard management practices that had potential to boost yield and/or improve manual labor efficiency in Oregon vineyards. Two field experiments separately evaluated dormant pruning practices and nitrogen fertilization.

Many Oregon vineyards are cane pruned rather than spur pruned, as yield is thought to be reduced due to low fruitfulness of basal buds left during spur pruning. However, spur pruning is of interest to growers since it can significantly reduce manual labor hours per acre during pruning and can be mechanized for further cost savings. In terms of nitrogen fertilization, it is often avoided in vineyards to prevent excess vine growth which can cause reduced wine quality, but vines are often N-deficient and lead to other wine quality issues such as low N in fruit and sometimes low yield. In order to help develop management guidelines for growers, we studied the impacts of pruning practices and nitrogen fertilization on Pinot noir bud fruitfulness, a component of yield. This research will be used to develop guidelines for growers in the region to produce more consistent yields over time while also fine-tuning practices that may effectively manage nutrient and labor inputs.

Project Objectives:

Objective 1: Determine how yield potential and final harvest yields are affected by cane and spur pruning.

Sub Objective 1: Obtain labor efficiency data from collaborating grower to determine the differences in observation between the two pruning methods. 

Objective 2: Determine how nitrogen fertilization of an N-deficient vineyard impacts yield potential (fruitfulness and fruit set) and final harvest yields.

Cooperators

Click linked name(s) to expand
  • Tim Scott
  • Ryan McAdams

Research

Materials and methods:

Objective 1: Determine how yield potential and final harvest yields are affected by cane and spur pruning.

This trial was conducted in a commercial vineyard located in Dayton, Oregon. The block consists of Jory silty clay loam soil and was planted in 2007 to Pinot noir (Pommard clone) grafted to 101-14 rootstock. The vines are spaced 1.07 m between vines and 1.8 m between rows and oriented north-south with a 20.1% slope. The vines are trained to a Guyot system with vertical shoot positioning.

Two pruning treatments were implemented in February 2017 and 2018 as follows: 1) Cane – vines were pruned by selecting one cane with 10 to 12 buds per vine with 1, 2-bud spur maintained at the head for cane renewal the following year, and 2) Spur—vines were pruned to 2-bud spurs with 5 to 6 spurs/vine. The treatments were applied to plots consisting of three consecutive whole vine rows in a randomized complete block design with five treatment replicates. Data were collected on the middle row of each block. Standard disease prevention and canopy management practices were employed by the vineyard management team with the exception of pruning, and cluster thinning was not conducted to allow for the quantification of potential yield differences at harvest.

Dormant bud fruitfulness assessment took place in January 2017, 2019, and 2019. In each plot, one dormant shoot was randomly selected from each of the 10 data vines per plot. The shoots were stored in a cold room at 4°C until analysis (within 5 days of sampling). Shoot weights and mid-internode diameters were recorded for each dormant shoot, and buds were examined with hand-dissection under a stereoscope to count the number of inflorescences per bud (FFL) and measure the sizes of the inflorescence primordia using a microruler. The inflorescence size was recorded as integrated fruitfulness index (IFI), and this is calculated as the sum of diameters of floral primordia within each bud. Each bud was assessed individually along the shoot in order to determine if node position is important for bud fruitfulness. Cane-pruned vines were assessed at nodes 1 to 12 and spur-pruned vines at nodes 1 to 5 to ensure measurement of buds that may be retained at pruning. The dormant shoot weight and  internode diameter provided data on cane vigor that was compared statistically with the bud fruitfulness and floral primordia size, as vigor may be related to increased fruitfulness based on prior work in the Skinkis Lab.

Actual fruitfulness (the number of inflorescences per shoot) was measured post-budbreak in spring 2017 and 2018 and compared to the bud fruitfulness measured during dormancy.  This was important to understand whether there was an impact of treatment on inflorescence development from the bud to shoot stages and/or quantify the differences that may exist in potential fruitfulness compared to what actually grows on the shoots. Other growth parameters were measured in spring 2017 and 2018, including shoot length, leaf area, and percent fruit set. Shoot length and leaf area were quantified on individual shoots of data vines pre-bloom and at bloom. Leaf area was quantified using a non-destructive template method where all primary leaves on each shoot are compared against a template with known leaf area sizes. The total number of leaves and size of leaves was summed (for two shoots per vine) and the average used to determine whole vine leaf area when multiplied by the number of shoots per vine. Leaf area was important to know between the two pruning methods, as growers have interest in the differences in early season shoot growth and canopy density between the two pruning methods as this can impact their canopy management practices. The percentage fruit set was quantified before bloom and at fruit set using a non-destructive photograph method where individual clusters were digitally photographed before and after bloom and then counted to determine the number of florets (pre-bloom) compared to berries (post set). This fruit set information was necessary to ensure that we were capturing the impacts of the two pruning systems on yield, as we recognize that yield can be impacted by fruitfulness (number of inflorescences developed by the vine) as well as the number of flowers set to berries. Whole vine yields were collected at harvest in 2017 and 2018 and compared to the fruitfulness data to determine an impact of pruning on yield. Dormant whole vine pruning weights will were measured in January 2017, 2018, and 2019, to determine any impacts of pruning on vine vigor not captured by leaf area data.

Because growers are concerned that pruning method will lead to a delay in ripening or differences in berry ripeness, we measured basic maturity advancement of fruit up to and at harvest. Fruit samples were collected on a weekly basis beginning three weeks prior to harvest for measurement of total soluble solids (TSS, Brix), pH and titratable acidity (TA). Whole vine yields and cluster counts were measured at harvest.  Fruit samples at harvest (7-10 clusters per plot) where analyzed for cluster size and architecture (cluster weight, berries per cluster, berry weight, and cluster compactness calculated) to determine if pruning method affected berry or cluster size. Berries were pressed to juice to be analyzed for TSS using a digital refractometer, pH using a pH-meter, and TA using 1.0 N NaOH titration to endpoint pH of 8.2.

Sub-objective 1: Obtain labor efficiency data from collaborating grower to determine the differences in observation between the two pruning methods. 

The grower collaborator maintained records of labor costs for vineyard management practices during the two growing seasons of the study. This included focus on the time it took to spur prune vs. cane prune and the number of passes required for shoot thinning in spring. We anticipated that spur pruning would be more efficient on laborer time compared to cane pruning, but spur pruning may require a greater amount of shoot thinning in spring that could negate the efficiencies or economic savings of the spur pruning during the dormant period. The grower collaborator also polled his crew leader for their observations in working between the cane and spur pruned vines during the growing season for the following:  1) general observation of differences in canopy or fruit, 2) ease of working with the vines, and 3) overall preference of pruning method.

Objective 2: Determine how nitrogen fertilization of an N-deficient vineyard impacts yield potential (fruitfulness and fruit set) and final harvest yields.

This trial was conducted in a commercial vineyard located in Amity, Oregon. The block consists of Saum-Parrett complex soil and was planted in 2005 to Pinot noir (clone 777) grafted to Riparia Gloire rootstock. The vines are spaced 1.0 m between vines and 1.75 m spacing between rows and oriented north-south. The vines were bilaterally cane-pruned and trained to a Guyot system with vertical shoot positioning.

There were two treatments, including one that received N fertilization and one that did not. The N-fertilized plots were supplied with three applications of urea through drip irrigation, each in the amount of 22.4 kg N/ha, at pre-bloom, pre-veraison (before the onset of ripening) and véraison (the onset of ripening), for a total of 67.3 kg N/ha in 2017. Similar applications were made in spring/summer 2018. The experiment was designed as a randomized complete block design with treatments applied to whole vine rows with one buffer row flanking each side of the treatment rows. Treatments were replicated in four blocks, and data were collected on 10 randomly selected vines from the middle row within each experimental plot. Vines were managed with standard disease prevention and canopy management practices, and non-fertilized vines were irrigated similarly as the N-treated vines.

Because we anticipated that N fertilization could enhance fruitfulness, we began looking at bud fruitfulness following each treatment year. The first year of bud fruitfulness was assessed in January 2018. One shoot was randomly selected from each of 10 data vines in each plot prior to pruning. Shoots were stored at 4°C until analysis (within 5 days of sampling). Buds were examined with hand-dissection under a stereoscope to count the number of inflorescences per bud (FFL) and measure the sizes of inflorescence primordia with a microruler, which is termed the integrated fruitfulness index (IFI) and is calculated as the sum of diameters of floral primordia within each bud. Each bud was assessed individually along the shoots (nodes 1 to 12) to determine if node position affected bud fruitfulness. Shoot length, shoot weight, and mid-internode diameters were recorded for each dormant shoot to provide a measure of cane vigor that could be compared statistically with bud fruitfulness measures, as prior work in the Skinkis Lab indicates a positive correlation between vigor and bud fruitfulness.

Shoot fruitfulness (number of inflorescences per shoot) was determined post-budbreak and compared to the bud fruitfulness measured during dormancy. This was done to quantify potential differences between bud fruitfulness and what actually grows on the shoots. In spring, other growth parameters were measured, including shoot length, leaf area, and percent fruit set. Shoot length and leaf area were quantified on individual shoots of data vines pre-bloom and at bloom. A non-destructive template method was used for leaf area quantification where all primary leaves on each shoot are compared to a template with known leaf area sizes. The number of leaves and sizes of leaves are summed for two shoots per vine, and the average is used to determine whole vine leaf area when multiplied by the number of shoots per vine. N-fertilization may lead to differences in early season shoot growth, thus it is important to determine leaf area. A non-destructive photograph method was used to quantify percent fruit set at pre-bloom and fruit set where individual clusters were digitally photographed and counted before and after bloom to determine the number of flowers (pre-bloom) compared to berries (post set). Yield can be impacted by fruitfulness (number of inflorescences developed by the vine) and the amount of flowers set to berries, thus the fruit set information helps us understand an additional component by which N-fertilization may impact yield. Whole vine yields were measured at harvest and compared to the fruitfulness data to determine wether our early measures align with final yield. Dormant pruning weights were measured in each dormant period (Jan 2018 and 2019) to determine the impact of N fertilization on vine growth and vigor of the prior season.

Fruit quality is a major concern for all wine grape growers, and many producers fear that fertilizing with N will cause vigorous growth and lower fruit quality. Fruit ripening samples were collected weekly, beginning three weeks prior to harvest, and total soluble solids (TSS, Brix), pH and titratable acidity (TA) were measured. Whole vine yields and cluster counts were also measured at harvest. Berries were pressed to juice for analysis of TSS using a digital refractometer, pH using a pH-meter, and TA using 1.0 N NaOH titration to endpoint pH of 8.2. Cluster and berry morphology measures were also measured, including cluster weight, berry count, berry weight, as these are often important yield components that growers and winemakers are interested in for aspects of yield and quality. Berry N was measured by another group as part of a larger project and was not included in this project.

Research results and discussion:

Pruning Trial Results

Bud fruitfulness: Bud fruitfulness assessed by node position on dormant canes (nodes 1-12) and spurs (nodes 1-5) did not differ in number of inflorescences or inflorescence size for nodes 1-5. Furthermore, our findings show that basal buds are fruitful in Pinot noir, whether from cane- or spur-pruned vines. This is an important finding since producers thought that they could not spur prune since Pinot noir as a cultivar had low or no floral primordia in basal buds that would be retained at pruning. Furthermore, the mean number of inflorescence primordia per bud and the sizes of the inflorescence primordia were similar in cane- and spur-pruned vines when statistically analyzed across all nodes assessed. The primary buds contained ~2 inflorescence primordia, and an additional ~1 inflorescence primordia was found in secondary buds.

Mean (+/- standard error) fruitfulness of cane and spur pruned vines at bud positions along the cane. 1 indicates the bud closest to the head of the trunk and 12 indicates the most distal bud position.

Regardless of the pruning treatment, the larger the cane size, the higher the bud fruitfulness across the three dormant periods that we observed bud fruitfulness. In 2017, at the outset of the study, there was higher bud fruitfulness found with greater cane internode diameter. In 2018 and 2019, the greater the cane weight, the greater the whole bud fruitfulness. In 2019, higher cane weight was related to higher floral primordia size in both the whole bud and the primary bud. This is important information, as some literature has suggested that high vine vigor leads to low fruitfulness and primary bud necrosis. However, we did not observe low fruitfulness or primary bud necrosis in this vineyard trial, and the vigor of the experimental vineyard was considered high.

Shoot fruitfulness, fruit set, and yield: In 2017, the shoot fruitfulness post-bud break was slightly lower in spur-pruned than cane-pruned vines with 2.2 and 2.8 inflorescences per shoot, respectively. In 2018, there were no differences in shoot fruitfulness with a mean of 2.9 inflorescences per shoot for both treatments. Cane-pruned vines had 37-47% more flowers per inflorescence pre-bloom and 24-33% more berries per cluster post-fruit set compared to spur-pruned vines across the two years. There was no difference in the percent of flowers that set to fruit in 2017, but spur-pruned vines had 6% lower fruit set than cane-pruned vines in 2018. Clusters at harvest were 23-27% larger in cane-pruned vines than spur-pruned vines, and this was due to having more berries per cluster. Yield at harvest did not differ between the two pruning methods despite differences in cluster size, since spur-pruned vines had a few more clusters (due to a few extra shoots) than cane pruned vines. It is important to note that there were no differences in berry size as a result of the pruning method; this is an important consideration to winemakers who prefer smaller berry size. The smaller cluster size is likely the result of smaller inflorescences that form in basal buds of the spur pruned vines and relates to other findings in research of the Skinkis Lab.

Vegetative growth effects: Spur-pruned vines had 19-25% heavier dormant whole vine pruning weights than cane-pruned vines following the crop years of 2018 and 2019. However, dormant cane weights from whole vine measures were not different with means of 102 g and 117 g for 2017 and 2018, respectively. The difference in pruning weights between treatments are attributed to spur pruned vines having 2-3 more shoots per plant than cane pruned vines. This data indicates that the pruning method did not affect vine vegetative vigor as measured by dormant cane weights. There were no pruning treatment differences in the vine balance (yield to pruning weight ratio). This is important as an indicator of adequate canopy to support fruit load, and helps to describe to growers that pruning method alone will not lead to unbalanced vine growth.

Yield and fruit composition: There were no differences in the onset of ripening and ripening advancement in this study. Fruit from both pruning treatments were able to ripen to commercial standards and were harvested on the same date. The fruit composition was as follows for the two seasons: TSS ranged from 23.8 to 24.1 Brix and pH was 3.3 in 2017 and TSS ranged from 21.5 to 21.7; pH ranged from 3.1 to 3.2; and TA ranged from 6.7 to 6.8 g/L in 2018.

The sub-objective of the pruning trial was to assess labor efficiency and economics of the two different pruning methods. Spur pruning vines required fewer labor hours than cane pruning. All of the pruning was conducted by the vineyard manager and assistant vineyard manager and time was documented. Spur pruning removed one pass compared to cane pruning, with an estimated 25% reduction in labor hours. There was slightly more shoot thinning required in the spur pruned vines, as extra shoots grew from the cordon, slowing down shoot thinning and/or requiring a follow-up pass in spring. The increase in shoot thinning was hard to estimate since shoot thinning was required in both cane and spur pruned vines in this vineyard. The vineyard manager prefers the canopy and structure of spur pruned vines and the efficiency of pruning. However, the crew leader preferred cane pruning due to the less adventitious shoots that grew on those vines compared to the cordon of the spur pruned vines. Although, the crews and crew leader were most familiar with cane pruned vines and may have simply preferred to work within a system that they were more accustomed. This finding also became important for understanding adoption. Many of the vineyards in the Willamette Valley are cane pruned, not just for Pinot noir. The crews and contract labor are not used to pruning or managing cordon-trained, spur pruned vines, and they would require training to ensure proper pruning techniques and canopy management in early spring.

Nitrogen Trial Results

The N-fertilized treatment had higher N status of leaf tissues at bloom and véraison compared to the control. However, the vines were at sufficiency or above sufficiency levels for N status during both years with 2.7-2.9 % N in leaf blades at bloom and 2.1-2.4 % N in leaf tissue at véraison. This is important information to consider when assessing the impact of N addition on yield potential (bud fruitfulness).

Bud fruitfulness: Bud fruitfulness was similar by year for the two dormant periods that they were measured. Nitrogen fertilization increased the number of inflorescences per bud (bud fruitfulness) by 19% and the size of inflorescence primordia (IFI) by 30%. These differences were found to exist in the primary buds, with N-fertilized vines having higher primary bud fruitfulness and inflorescence primordia size. Primary buds are typically the buds that grow out first at the budbreak each season, so this increase may be realized in final yield at harvest. Dormant shoots measured prior to bud dissections did not vary significantly from each other in weight, length, or diameter, except for a few measures in 2018 and 2019, including the following:  N-fertilized vines had longer shoots at dormancy in 2018 and larger cane diameters in 2019 compared to the control. These data indicate that the N-fertilization was not enough to cause major shifts in vine vegetative growth or cane vigor. However, regression analyses of cane size data with the bud fruitfulness measures show that greater cane weights had higher whole bud fruitfulness and greater inflorescence primordia size of the primary bud, regardless of N or control treatment.

Regression relationships for 2018 and 2019 bud fruitfulness parameters and dormant cane weight and diameter in Pinot noir grown in an Oregon vineyard. Each dot represents a plot mean. A. Cane weight and whole bud fruitfulness; B. Cane diameter and whole bud fruitfulness; C. Cane weight and integrated fruitfulness index of the primary bud, and D: Cane diameter and integrated fruitfulness index of the primary bud.

We conducted correlation analyses of leaf and petiole N status from the years prior to the bud fruitfulness quantifications. Results show that veraison leaf N correlated with fruitfulness and inflorescence primordia size of the whole bud and the primary bud.

Buds were more fruitful at more distal nodes on shoots of N-fertilized vines compared to the control. In 2018, there were more inflorescences in the whole bud of N-fertilized vines at nodes 5,6,7, and 11 compared to the control. However, there was only one node in 2019 that was higher fruitfulness (node 8) compared to the control.

Shoot fruitfulness, fruit set, and yield: When shoot fruitfulness was analyzed post bud-break, there were 0.3 more inflorescences per shoot in N-fertilized vines compared to control vines. Although this increase seems small on a per shoot basis, it equates to 0.91 ton/acre difference in yield across an entire block if the inflorescences become clusters. The N-fertilized vines also had larger inflorescences than control vines in 2018, but there were no differences in the percent of fruit set compared to the control. There were no differences in fruit yield by harvest in 2018, with vines having 1.4 kg/vine. This is not too surprising since the vineyard management thinned crop to yield targets, and both treatments were able to meet their production goal.

Vegetative growth effects, vine balance, and fruit composition: There were early season differences in shoot growth during 2018, with N-fertilized vines having longer shoots before bloom. However, there were no differences in leaf area by late summer (ripening). There was no difference in whole vine pruning weight after year one of the trial; however, by year two, N- fertilized vines had 30% higher pruning weights than control vines in winter following the crop year 2018. There were no fruit composition differences for basic ripeness parameters (sugars, pH, and titratable acidity) in 2018, indicating no issues with basic fruit composition. The yields did not differ between N-fertilized and control and were sufficient for commercial production standards, and fruit ripeness was optimum for wine production, with harvest fruit composition in 2018 being 23.8-24 °Brix, pH=3.3, and TA=5-5.3 g/L.

 

Participation Summary
2 Farmers participating in research

Educational & Outreach Activities

8 Consultations
1 Curricula, factsheets or educational tools
1 Journal articles
2 On-farm demonstrations
1 Online trainings
2 Published press articles, newsletters
13 Webinars / talks / presentations
2 Workshop field days

Participation Summary

350 Farmers
10 Ag professionals participated
Education/outreach description:

Eight presentations have been given by the graduate student (n=3) and lead PI (n=10) in 2018-2020, including numerous industry seminars, a poster at an academic conference, a poster at an industry conference, one workshop and one field day. The graduate student involved on this project worked on an extension newsletter article while she was finishing her graduate studies and was completed by the PI and published in the Oregon Wine Research Institute Vine to Wine Newsletter in fall 2019. One peer refereed manuscript from the pruning trial was submitted and accepted for publication by Catalyst: Discovery into Practice in June 2020. A second manuscript is still under development. This work is also published in the MS thesis of the graduate student on the project.

Project Outcomes

100 Farmers reporting change in knowledge, attitudes, skills and/or awareness
10 Farmers changed or adopted a practice
25 Farmers intend/plan to change their practice(s)
1 Grant received that built upon this project
Did this project contribute to a larger project?:
Yes
1 New working collaboration
Project outcomes:

The growers requested this research because they wanted to know if they could spur-prune their vines to reduce labor costs. Estimates at present are that growers will be adopting this practice of spur pruning which will reduce labor hours per acre and will be further reduced with mechanical pre-pruning, which is only possible with spur pruning (not with cane pruning which is the current industry standard). A recent economic analysis by a fellow OSU agriculture economist indicates that mechanizing pruning practices has the greatest economic return on investment for grape growers with smaller acreage which describes the Oregon industry. However, there are further cost savings for larger producers as well. We believe that California Pinot noir producers will also be looking to this work and may shift their production practices as a result of this work. 

The nitrogen project has some potential for economic benefits, as many growers are currently not using N in their vineyards, and they could be increasing productivity and vine health if they were to implement a moderate N fertilization program. Furthermore, we showed that with minimal N inputs, they can have an impact on fruitfulness and yield potential, and that large inputs are not required. In prior work, we found that N management through cover cropping may be a suitable alternative for the N fertilization inputs used in this study. 

This project allowed growers to have more confidence in their vineyard decision-making by providing them with data that fit with their prior thought, for example, that changing pruning method would not be detrimental. However, growers of wine grapes often have wineries and winemakers requesting the vineyard management practices adhere to the status quo, often against the better judgment of the farmer. Furthermore, they often cannot make these decisions without data to support them, and we provided them with this information. We hope that further social benefits will come as they toss aside borrowed wisdom from European grapevine production regions (or other regions) and rely on the results they have on their site/region/state.

Knowledge Gained:

This project helped us generate information that allowed us to provide growers with recommendations on how to change their production practices without the risk of the unknown. By working with growers, we were able to develop skills in communicating with growers to understand how the practices we were evaluating in our two trials were going to help the industry. We learned how to set realistic treatments for the field, knowing that what we tested had to be something the grower could see implementing without issues. For example, we tested two types of pruning methods that they could do and did workshops on showing growers how to do the unfamiliar method of pruning (spur). We also set the N fertilization levels to that of what would help improve wine quality without causing extra growth they had to manage. It resulted in lower impacts on a bud fruitfulness and yield level, but it was within a realistic range of N application. In the process, we were able to also understand the limitations they are faced with and the production goals they strive for. Economic sustainability is harder for them to realize than environmental sustainability. Our project had more economic sustainability potential than environmental. Understanding what they need and how to help them was the biggest realization in this project. 

Success stories:

Several growers in the premium Pinot noir growing regions of Oregon changed their pruning practices in winter 2019/2020 after hearing results during seminars and workshops. A few growers mentioned converted areas of their vineyard to spur pruning as a test in winter 2018 and 2019, and this led to similar observations in our study. The result is that they had plenty of fruit of good quality that is not impaired by the pruning method. One grower said that the winery they sell to prefers spur pruning, and they will be expanding acreage that is spur pruned.

More growers are starting to conduct mechanical spur pruning in the Willamette Valley and areas of western Oregon, as we have had reports of more mechanical pre-pruning implements being purchased in 2019 and 2020. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.