Season 3, Episode 1 | Grapevine Capacity for Change (in English)

00:00 Patty Skinkis

This is the HiRes Vineyard Nutrition Podcast, devoted to helping the grape and wine industry understand more about how to monitor and manage vineyard health through grapevine nutrition research. I am your host, Dr. Patty Skinkis, Professor and Viticulture Extension Specialist at Oregon State University.

00:22.00 Patty Skinkis

Back in season one, we had an episode that featured nutrient management in arid climates. Dr. Marcus Keller spoke about the practices used in eastern Washington and the unique challenges they face in that climate. Markus Keller is the project director of the HiRes Vineyard Nutrition Project, and he is here with us today to give an update on the research he is conducting in Washington to understand how to align sensor technology to detect vine nutrient status with focus on field and lab-based nutrient trials that are conducted in his program. Dr. Markus Keller is the Chateau Saint Michelle Distinguished Professor of Viticulture at Washington State University’s Irrigated Agriculture Research and Extension Center located in Prosser, Washington. He has a wealth of knowledge in both practical viticulture and vine physiology. We're glad to have him join us today.

01:15.00 Markus Keller

Hi Patty, it's wonderful to be back again! I can't believe it's been such a long time already since the last time, but you've done a series of these podcasts with a lot of people in the project, so I guess it's time for me to say something again about the project.

01:33.00 Patty Skinkis

Absolutely! We're glad to have you back. We had a number of people from your lab talk about interesting projects, and so we've gotten a little insight into those individual projects that are part of your entire umbrella. I thought it would be great to have you bring those pieces together from the higher viewpoint. To start out with, can you tell us about the research that you have been conducting from the bigger picture view and speak to the progress you've made in the last couple years.

02:03.00 Markus Keller

Our work within the overall project has been mostly to run some field experiments. We've done a mix of field and potted vine experiments over time. We've worked with different varieties, wine and juice grapes, red and white wine grapes, with commercial collaborators like Chateau Saint Michelle (or Saint Michelle Wine Estates) and then a juice grape grower in Sunnyside, Washington. They have supported our work, and we've applied different rates of nutrients, for example nitrogen or potassium fertilizer, to generate differences in nutrient status in the vines, mostly to support our engineers in their effort to try and remotely sense [the vineyards] with hyper-spectral or multi-spectral cameras that sense the nutrient status of the vines. In doing so, that gave us an opportunity to look at what happens to the plants, especially to fruit production, yield, and fruit composition. We've collaborated with the Wine Science Center at the Tri-Cities campus of WSU that's managed by Dr. Jim Harbertson, who is a cooperator (Co-PI) in our project, to make wine from the different nutrient rate treatments that we have applied. This is to see if there are any effects on the actual wine composition, wine quality and so on. Those are the main experiments we’ve been conducting. Then we've done some pot experiments looking more precisely at nutrient uptake over the growing season of grapevines, addressing the questions of when they start taking up nutrients through their roots, and how does it progress through the season. Is there an effect, for example, of temperature when we have a heat wave? Does that influence how nutrients are being taken up by the vines and so on?

You were asking about progress--what have we found, and of course, I could talk for a few hours now just detailing on little things that we have found out. But in a bigger picture of things, one thing that struck us was how difficult it actually is in the field to change the nutrient status of a grapevine or of a vineyard. We've been applying up to 80 pounds per acre of nitrogen, for example, for three or four years in some of these field trials, and we find tiny little effects on the leaf or the leaf blade or petiole nutrient status. When we really look, we do find effects, for example, of nitrogen supply on YAN (Yeast Assimilable Nitrogen) in the fruit that increases with the more nitrogen we apply. But It's interesting that even a small dose of foliar nitrogen applied around veraison is as effective as much higher doses of soil applied nitrogen if your goal is just to increase YAN, for example.

The question then became: well, okay, we can increase YAN, but does that change anything else in fruit composition? One thing we have found, and we're working with Syrah, for example, we found that as you apply more N (more nitrogen), either on the leaves or on the soil, we tend to decrease tannins in the fruit. So, now we're going to go and see with Jim Harbertson what might cause that decrease in the tannins. That was interesting to find--that you can change fruit composition. We've known some of this before, but the focus in the past had been more on anthocyanins, and we're not finding very big effects on anthocyanins in Washington. The bigger effect is on tannins, especially skin tannins in this case.

05:59.00 Patty Skinkis

With the nitrogen, why do you think that it's not having as much of an impact on the field application? Is that a soil or fertigation application versus the foliar?

06:09.00 Markus Keller

So, that's hard to know. I'm assuming you're asking about changing the tissue nutrient status, right? With applications, I think vines, in general, are just very well buffered. They're a perennial plant. They use reserves to start their growth early in the growing season. They rely entirely on what they have accumulated in their trunk and roots the previous several seasons, sometimes, and the fact that this occurs over several seasons tends to buffer whatever we apply in any one particular season.

So, we're not farming in viticulture for just one year; we're farming for two or three years at the same time, and that's something we tend to sometimes forget. It's difficult to change nutrient status because vines can buffer from internal reserves, and they also can change where their roots go. When you think about where most of the nutrients are in the soil, it's usually in the topsoil, but with nitrogen in particular, that gets converted to nitrate quite quickly in the soil and then leaches down in the soil profiles, so deeper roots often end up taking up more nitrate from lower levels in the soil profile that we forget to account for sometimes because maybe we focus too much on just the topsoil. There's lots of things that are going on in grapes, but overall, they just are very good at buffering their nutrient status over time, which, of course, has implications for fertilizer management. Maybe we shouldn’t worry too much about changing little things, you know, turning the screw just that very little bit in any one growing season, and take a step back and manage over multiple seasons. As long as we don't let these vines go into deficiency situations, we're often fine! We can back off nutrient supply to the level that we're just applying to maintain a nutrient status in these plants.

08:07.00 Patty Skinkis

That makes a lot of sense. When you were talking about your field trials and nitrogen, you have these potted trials, which I assume were created to help pinpoint more specifically what the vine was doing without the background of that commercial setting which you said the vineyard trials —the field trials —were in commercial settings. Just off-topic question--were the vines that you use for the trials own rooted, or were they grafted?

08:39.00 Markus Keller

Good question. Washington still is almost all own-rooted. New vineyards are now going into rootstocks, but we've been working with what we have in the commercial vineyards, and they're all own-rooted, all ungrafted plants. So, with our pot experiments, we've done the same thing with used own-rooted plants. I'll give you an example: we used Cabernet Sauvignon in a very artificial medium. The plants are obviously not artificial, but the soil is not soil--it's perlite, pure perlite. Then we had these mini lysimeters that a postdoc of mine ran, Tom Groenveld. He used to be the project manager and then did some experiments on the side, and measuring precisely how much nutrient he applied, and how much of that was leached away from the soil, and how much is taken up by the vines. He found that there is essentially no nutrient uptake before about the 5 to 6 leaf stage of these vines. So, the roots have to start growing before they take up nutrients, and then they're able to take up nutrients from that point on, almost linearly throughout the entire rest of the growing season until the leaves fall off.

It's not like we used to think, there are two peaks of nutrient uptake — one around bloom time and the other one post-harvest or something like that. If nutrients are available and the temperatures are conducive, and soil moisture is high enough, they will be able to just take up nutrients throughout the growing season, which is an effect that is driven by growth. So, the vines take up what they need.

The other thing that came out very loud and clear from this artificial perlite experiment is the more you apply the more they take up, but the less efficient these vines become at taking nutrients up. So at low levels of nutrient supply, for example, we found that about 75% of all the supplied nitrogen in this case was actually taken up by the vines. But at high levels of supply, as the supply increased in steps, that uptake efficiency dropped to about one-third —so only 33% of the supply nutrients were being taken up. When you then superimpose a heat wave on top of that, the uptake efficiency dropped to only 25%.

So, big implications for fertilizer management from a very artificial experiment is this: don't apply too much, don't apply too early, and don't apply too much at one time. It's much better to spoon-feed these vines, break nutrient supplies down into several smaller doses over time during the growing season, and back off nutrient supply when there's a heat wave coming when it gets too hot.

11:32.00 Patty Skinkis

It will be interesting, and it's hard to do that work. It’s always the challenge when you hear about these potted trials that give us some insight and then to try to take that to the field. I suspect if you tried to do like spoon feeding it in the field, you'd basically find very little impact. Do you think that will be the case?

11:54.00 Markus Keller

Yeah, over time, exactly. We do, I mean, my approach has long been to kind of spoon-feed it. In the western US, we apply most nitrogen anyway, and in many cases, other nutrients as well by fertigation, and that does allow us to spoon-feed. We typically break down, let's say, nitrogen supply. If we apply 30 or 40 pounds per acre, we break that down into 10-pound doses starting at the 5-leaf stage, and then a pre-bloom, and then a bloom or fruit-set duration. Then we typically back off and stop applying, so we would usually not be apply anything more than about 10 pound per acre at any one time.

12:32.00 Patty Skinkis

Very interesting. So, how about some of the other projects —the potassium work that you've been doing? Any major findings there?

12:41.00 Markus Keller

So, what we were expecting to find with the potassium was that the more potassium we applied, the more the vines would take up, and the worse effect would be on the pH of the fruit. This was an experiment we deliberately did with Chardonnay, where high pH can be an issue sometimes, and we wanted to see if maybe supplying low doses of potassium could help us increase the pH in the fruit. And of course, we've been doing this for four years now, and of course, we're finding nothing. There's no effect on pH. There is not even an effect on the potassium in the fruit. It's very hard to even find an effect on potassium in petioles or leaf blades.

To me, when I go to that vineyard, the low-potassium vines look potassium deficient. So, there are things going on in these vines that are compensatory, again, that we do not understand. There is a more to what goes on inside the vine that moves nutrients around to make sure the fruit and even the leaves get what they need. There's a lot more that we just haven't figured out yet that we need to understand.

13:48.00 Patty Skinkis

Did you do any potted trials with the potassium, or were those only field trials?

13:54.00 Markus Keller

We did a potted vine experiment as well with potassium, with the exact same result, and then we concluded in the pot experiment that was early on in the project, “Oh maybe the soil already contained too much potassium.” This was an actual soil experiment in the pots, not perlite, and so then we stopped doing this. The student that was doing this lost interest in the potassium work, and we focused just on the fieldwork and lo and behold, same result. We're all scratching our heads, thinking, “What should we do next?” right.

14:26:00 Patty Skinkis

Well, I think that goes to show too that sometimes the “no result” or “no significant result” is also a result, you know, and it's not so clear with potassium. I know that similar work here in Oregon with potassium wasn't very clear either, so it's nice to see that at least we've got, with this project, some similarities popping up in very different regions with different soils.

14:51.00 Markus Keller

Consistency in the inconsistency, or in the unclearness, anyway. And to me, that's surprising because the other thing that we found in these field trials is how much potassium we're actually removing from a vineyard at the end of the growing season. In a wine grape, we typically take out 20 to 60 pounds per acre of potassium just with the fruit that we're harvesting, depending on the crop yield, of course. There's a range of 20 to 60 [pounds] but with juice grapes that can go up to 100 to 150 pounds s per acre. So, we're removing substantial amounts of potassium from vineyards with the fruit that we're harvesting, and at some point, we need to replace that potassium, or we are going to run into deficiency situations. On top of that, we're also losing potassium often at the end of the season with the leaves that fall off from the canopy, and it seems like that is the case more so when an early fall frost kills off the leaves. The leaves typically recycle their nutrients, take them back to the plant, and it goes down to the trunk, then the roots for next season. But when a fall frost kills the leaves off, which happens a lot in Washington and northern climates, then we lose all those nutrients. They can go back to the ground in the leaves, but then we often have windstorms in the winter with very little cover crop because it's too dry to grow a big cover crop during the season, and then often these leaves end up in an alfalfa field or another field next to the vineyard instead of being recycled back into the vineyard.

So, if you are having a nice cover crop that traps the leaves on the ground, then you have more recycling going on at the end of the growing season. If you're growing season, like you're going to California with these longer post-harvest seasons, there's more opportunity for the leaves to recycle those nutrients. But having said that, one of the surprises that I experienced here was that we lose about as much magnesium with the leaves as we do potassium at the end of the growing season. I was not expecting it. I should have probably expected it because magnesium is in chlorophyll and so on, but I was just expecting it to all be recycled. That doesn't seem to be the case here, so we can lose somewhere between 5 to 10 pounds of magnesium in the leaves at the end of the growing season, and that's substantial. If we don't replace that, I think that is one main reason that in cooler climates, we tend to often observe magnesium deficiency. We forget how much we tend to lose with the leaves If we're not accounting for that.

17:34.00 Patty Skinkis

You bring up a really good point because here in Oregon, where we have a cool climate, we see magnesium deficiency. We don't usually see potassium deficiency, but we do see magnesium deficiency in some vineyards in some years. So, it's kind of interesting to hear that.

17:50.00 Markus Keller

It's the same in Switzerland. I am from Switzerland, and I was used to vineyards just displaying magnesium deficiency — that was just normal. It's normal in many parts of France as well. It's like, ‘Oh, they're just magnesium deficient,’ but why hasn't it occurred to us that maybe we're just not accounting for all the losses that we incur at the end of the season?

18:10.00 Patty Skinkis

Maybe because we focus so much on N, P, and K that we don't focus on the others, and there's some links there.

18:19.00 Markus Keller

And if we do budgeting--nutrient budgeting--which is one thing we're working on at the moment —then we often focus just on the fruit. We don't focus on anything else on the plant.

18:29.00 Patty Skinkis

That's a good point. You know, one of the things people ask a lot about is hedging and how hedging, or leaf pulling, or all this canopy management can be influencing the vines. We don't capture that or even fruit thinning, here in Oregon. All of those factors and losses don't come into that final harvest budget and nutrient budget. Do you have a sense for how much you might lose through canopy management? Afterall, we know that canopy management can help manage potassium in high-potassium situations. Do you have any sense for how much potassium status might be influenced by canopy management?

19:05.00 Markus Keller

I don't, and you know, obviously canopy management is something we try — I shouldn't say this too loudly — is something we tried to stay away from in Washington if possible. We try to control shoot growth with irrigation, ‘deficit irrigation’, because it's so dry we have the luxury to do that. So, we don't usually, if I have to hedge or top my vineyard, I'm embarrassed because I think I've done something wrong with my irrigation management.

19:34.00 Patty Skinkis

No, you're absolutely right. Yeah, here we can't control it, so we just get overgrowth. We have to manage it. Yeah, it's a good point.

19:41.00 Markus Keller

Many, many years ago, I did a postdoc at Cornell in Upstate New York in Geneva, and I did a field trial with Pinot noir where I hedged, and I was looking at nitrogen uptake or nitrogen effects on the fruit. And it turned out that the worst combination for quality, in terms of anthocyanin accumulation and so on for the wine that was made, was with multiple hedging, constantly getting the plant to invest new resources into growing new leaves and then cutting them off again after the plant has already built those leaves. Yet another reason to try and stay away from those things, or use leaf removal. I know this is very common in cooler climates where you have to expose the fruit to sunlight, and you have to get better spray coverage and so on. Again, we're moving away from much of that in Washington because we have sunburn issues; it's getting too warm, especially the west side of the canopy. But yeah, and this is a mostly unexplored area: what does canopy management actually do to the nutrient demand and the supply side for nutrients?

20:56.00 Patty Skinkis

So, with all the projects that you have done, you talked about this a little bit already but, what is the most surprising thing to you versus what you had expected? You know, what are… if you could pick …the ‘oh yeah, we knew this was going to happen’ versus the surprising parts.

21:12.00 Markus Keller

There are many things that we kind of expected but not as clearly, like how these vines resist responding to nutrient supply. Even in like the Syrah vineyard, for example, we're applying up to 80 pounds per acre of nitrogen in this vineyard, and first of all, we're seeing very little response of YAN in the fruit. We do see a response, but we're still way below what would be considered adequate YAN in the fruit, like much less than 150 milligrams per liter and so on—what winemakers might consider more or less adequate— even with consistently applying 80 pounds of nitrogen. So, the reluctance of vines to respond to nutrient supply, I was not expecting that to be this pronounced. This was true, like we just talked about earlier was true both for nitrogen and for potassium, but we haven't tested any other nutrients, so I can't comment on those. But I would be surprised if it was different for those other nutrients.

The other thing that surprised me—something we already discussed earlier —was that loss of magnesium late in the growing season. The fact that we lose, with the leaves, as much magnesium as we lose potassium. I was expecting it to be like an order of magnitude less, and it's not just in the same ballpark; it's the same numbers. That was a surprise.

22:40.00 Patty Skinkis

In terms of the work that you're doing, do you feel like this is worth investigating further?

22:48.00 Markus Keller

So, we obviously need to work more on the actual sampling. We haven't really talked about sampling for nutrients, petiole samples, leaf blade samples — when should you do it, how much, and so on. This is something we need to continue working on because we don't have a lot of lab results by now but not a lot of clear-cut conclusions. One thing that we did find was that, and this was especially pronounced with juice grapes —Concord juice grapes — we were applying high levels of nitrogen to the vineyard, is that the petiole is very much a nitrate storage organ. That is something and I was not expecting to be this pronounced, as well as we often discount petioles as just a pipe and they're moving nutrients through to the leaves or out of the leaf. But they do store orders of magnitude more nitrate than the leaf blade does, and that was one of the surprises and something that we need to explore a little bit more.

And then as you go later into the season we find that with high nitrogen supply, nitrate ultimately tends to accumulate in the leaf blades as well. Yes, it first starts in the petioles at much higher levels, and then later in the season in the leaf blade. I now think that whenever we find significant amounts, any real measurable amounts, of nitrate in the leaf blade around veraison, that is an indication that maybe we've overdone it with fertilizer supply. But I'm saying this as if I already knew that this was the case, but we have indications that that we might be going towards that recommendation. I really would like to see everybody else’s results in the team. I'm talking here about the results we got from Washington, but we need to look at the ones that Paul Schreiner has from Oregon, and then Matt Fidelibus has with table grapes and raisin grapes in California, the Virginia team has in Virginia on some hybrid grapes as well as Chardonnay. I would love to integrate all these results and see if we can come up with some common recommendations.

For example, is there just a continuum of YAN — if you supply ‘X’ amounts of nitrogen, does it continue to increase YAN in the fruit depending on the climate, or does each climate have its own unique YAN signature, or maybe each soil does? Those are things we don't know about yet, and then we need to figure out more about when to sample. For example, one thing we've done is we also sampled whole shoots at the five-six leaf stage. So, this was a consequence of finding that there was essentially no nutrient uptake before that stage, and we were saying, well, this is about the stage when many growers do shoot thinning anyway. So, it would be very easy for them to just pull off some extra shoots, and send them to the lab, and analyze the entire shoot with leaves, and petioles, and the actual shoot, plus the inflorescences and tendrils —everything included.

It does seem that that approach might have some promise as an indication of the reserve status of the vine going into the season. Like I said, if we have lots of nutrients from the plant because of wind or early fall frosts, or whatever and that might become reflected in the reserve status of the plant and that would then show in the shoot early in the growing season. That would allow us then to correct any potential deficiencies by supplying nutrients, which is not what we currently do. We currently collect petioles or leaf blades or both at bloom or, and, or veraison and often it's already too late by that stage to do much about it, right? So, that early season sampling is kind of encouraging to see that there is promise in using that. The problem with that, and I will shut up in a second. The problem with that of course is that we have no guidelines. What level of N, P, K is adequate in the shoot at the 5-leaf stage, we don’t know at this point. But we do know that there are differences, so we are going to explore this a little bit more, I think in the years to come.

27:17.00 Patty Skinkis

I was really excited about the 5 to 6 stage shoots because, like you said, it's when everybody's doing their shoot thinning practices anyway, so let's just use that material. And I think it's exciting to think of it from the reserve standpoint, because I personally feel like that's a timeframe that people overlook just in production. They don't think [about it], they're not plant physiologists, they're not thinking about what's in reserve, and it also makes a lot more sense to be more prescriptive in that regard.

And the one thing, I'm not sure that the teams doing the sensor work are sensing the shoots at that stage. I know we've started with our baseline at bloom and veraison, but did the Washington Team scan vineyards at that [5-6 leaf] stage?

28:04.00 Markus Keller

They did, but then they backed off because the sensors have a hard time picking out shoots from background at that stage. The shoots are just not long enough, so the sensor —the camera —has a hard time finding you know, ‘is this a shoot? is it something in the background? cover crop?’ Something we've talked about is maybe moving the sensor lower. It certainly won't work with a drone, for example, because you're looking down on the canopy, and the cover crop is often, if you have one, very green at that stage still. So, it's almost impossible to distinguish between a shoot and whatever else there is in the vineyard. We've talked about mounting a camera on an ATV but mounting it low, looking up towards the sky from below, and they're playing with that idea a little bit. But so far, they've been fairly discouraged by this early shoot sampling, and that is a bit of a drawback, of course. We are saying, ‘Hey, from our sampling tissue sampling approach, this will be a good stage to sample,’ but then the engineers are having a hard time making that actually work in the vineyard.

29:11.00 Patty Skinkis

Sure, and that makes a lot of sense. You're absolutely right; there’s lot more green to sift through in the background. And I think that's kind of one of the main goals of the project, as we've discussed earlier, is to bridge that gap between what we've always done and improve that and come up with these new methods. So, what do you think would be the next step for bridging that gap between our traditional practices and employing the findings from this research team and the combined work of the sensor technology?

All the teams, whether they're in Washington, New York, or California, are using similar sensors, and I think we've all come to the agreement that we, viticulturists are very set to what we know already--which is bloom and veraison. But I think a lot of them are interested in making something work for across the whole season and return more time points. So, do you think that's a reasonable thought, or do you have any ideas about how to advance this further?

30:14.00 Markus Keller

Absolutely, I think more time points would be valuable, especially more early season time points, and maybe we need to focus a little bit more on and the fruit as well to see how can we manipulate YAN more in the vineyard. For some reason, in drier climates —and, you know, yes, we're applying deficit irrigation — but we’re not truly water-stressing these vines to any great extent. They're under a little, you know, mild to moderate stress, okay, but we're just not getting, our YAN levels can be below 50 milligrams per liter. That's ridiculously low, and they vary from season to season. We're not sure exactly why they often vary by a factor of 2 when we apply the same management practices, same nutrient supplies, same irrigation approach. That is still variable by a factor of 2. What causes that? I would love to figure that out. And so, more time points for sampling early in the season would be good.

But I remember when we first met for this project, a very famous viticulturist who works for a very large wine company in California told us that ‘Hey guys, if you figure out this remote sampling for nutrients, that will be a landmark —a true breakthrough for this project. Anything else, I don't really care about what you find.’ And I think he was right about that. You know, if we can make this remote sensing work reasonably well, being scientists, we expect a very high accuracy, and we expect a one-to-one line with what we're sampling on the ground versus what they find with remote sensing with their cameras. And that may not even be necessary. Maybe we're just all overthinking that part, and if we could just classify vines into deficient, adequate, or excess —or even just deficient and everything else —that would bring us a long way for fertilizer recommendations. And would enable mapping of vineyards and then it would enable variable rate applications, not oversupplying nutrients where the wines really don't need them, and only focusing on those sections of a vineyard where nutrients are actually needed over the years. So, I do think we need to focus a little more keenly on this remote sensing approach, see what we can… well, make sure that we can make it work. But that requires a lot of on-the-ground sampling and that is tedious, it's costly, it's very slow. And this has been one of the limitations with the remote sensing is that they have to develop their models based on the nutrient data that we supply them from the tissue samples. And if it takes two or three months in the lab, then they're stuck; they have to wait for the data to come in. So, it will be nice to be able to speed that part up a little bit.

33:19.00 Patty Skinkis

Yeah, absolutely! I think you brought up a good point of the expectation of industry versus what we do as academics and researchers. We want to have that specific, detailed answers. But as an extension viticulturist, I know the world is not so clear. The vines are not so clear, and I think even just being on the project and learning about the results and seeing sometimes the frustration of the research team to not get an answer, I think the great thing is the Advisory Committee we've had that has given us like, ‘Hey guys, we're not asking you for this, we want this.’

I mean they're both aligned, but they're saying this is good enough. You know, people can't manage their vineyards to that extreme precision, but it's getting closer than just saying, ‘I don't know.’ But I do think some of the results of this study are really great, and that you know, these unanswered questions that… unless we do the work, we just don't know. And having any new information can then be used by the team to understand how to move forward.

34:27.00 Markus Keller

Well, I agree. I think the good thing of having to support the engineering approach, the sensor approach, the remote sensing approach, and so on is that it forces us to look more closely at the rest of the sampling that we're doing. Looking closely at what these tissues are telling us, what we finding there, how do they relate to each other, and how do they change over the growing season. That enables us to hopefully develop some better, more modern nutrient management strategies over time. But it's a long, slow process, and this is something that the industry sometimes tends to underestimate. Nutrition work, in particular, is slow in the field because these vines take such a long time to respond to nutrient supply and differences in nutrient supply.

35:19.00 Patty Skinkis

Absolutely, I agree it is a slow process, but I'm glad we've been able to do this work and hopefully make a little bit more progress on the path to getting more clarity.

Thank you so much, Markus, for your time today and for sharing the overview of some of the work you've been doing. We appreciate your time.

For those of you listening, I hope you'll check out more information about the project at our website https://highresvineyardnutrition.com/.

35:45.00 Markus Keller

Thank you, Patty, it's been a pleasure talking to you.