Know your vines #7: How to optimise your yield prediction and the power of the Yield Predictor Tool – PART 2
In our Know your Vines blog series we share practical tips on what metrics to monitor in your vineyard. This is the seventh instalment, stay tuned for more as the seasons unfold! “If you can’t measure it, you can’t improve it.”
Use bunch weights at lag phase and veraison to optimise yield prediction
In part 1 we looked at optimising your yield prediction by getting accurate bunch counts. As we move through the season there is more information available to us, allowing for our yield predictions to be optimised even further. Part 2 of yield optimisation starts with weighing actual bunches in lag phase, or at veraison, and then again at regular intervals in the run up to harvest. Last-minute losses due to disease can also be taken into account at this stage. Many thanks to Luke Spalding at Chalk House Vineyard for sharing his tips and tricks for getting a good yield prediction.
Third prediction: Weigh bunches at lag phase or veraison
For the next step of your yield prediction it is time to start weighing your bunches! This can be done at lag phase, or veraison. Weighing bunches at this stage you get a better idea of what the bunch weight will be for each varietal this year. Theoretically lag phase is about 55 days after 50% flowering*. In fact, this is one reason why recording 50% flowering is important – so you can identify when lag phase will happen.
*This is based on studies done with Pinot Noir in Oregon State. In more variable cool climates, like the UK, due to the stop-start growing season impacting both flowering and grape berry development stage II (lag phase), the number of days can vary much more (It’s important to always be observing!).
The lag phase prediction method is often thought to be the most accurate when done correctly, however as Chalk House vineyard manager Luke Spalding explained, “For many people the best time to start weighing bunches is veraison – it’s easy to see when that is, so you don’t have to worry about counting the number of days since 50% flowering for each varietal. The issue is that for some vineyards, waiting until veraison is too late, they need to be able to get a more accurate yield prediction as early as possible.”
Whether you choose to start measuring actual bunch weights at lag phase or veraison, the method is very similar. You need to go out and randomly select as many bunches as is reasonable from each block (Luke recommends 15-25 bunches per 1000 vines for smaller vineyards). We have seen a number of different methods used by different vineyard managers to select random bunches in a bay. Two options are:
- Select a mix of 1st, 2nd (and 3rd bunches if you have them)
- Select every other bunch in one random bay
Once you have selected your bunches from the block, you are now ready to weigh your bunches. You just need an average bunch weight, so if you know how many bunches you picked, then you can weigh them all together and divide the total weight by the number picked to get the average.
Use the bunch weight multiplier
Yield prediction calculation using bunch weights and multiplier
The rule of thumb is that in a ‘normal’ year, your bunches will increase in weight by a factor of 1.65-1.9. We call that number the weight multiplier. The multiplier differs for lag phase and veraison.
At this point you start to really optimise your yield prediction to be much more accurate. This is the first time you have got a real idea of the bunch weights for this year. Go to the yield predictor tool, enter in the average bunch weights for each block, and adapt the multiplier to ~1.65 for veraison weights, or ~1.8 for lag phase weights. Of course getting the multiplier right is key, which is why it’s important to measure bunch weights at lag/veraison each year, and then again at harvest. This allows you to understand the weight multiplier for each of your varietals/clones. If you don’t have any previous data then using a weight multiplier of around 1.65 (veraison) or 1.8 (lag phase) initially is a good place to start.
Optimising yield prediction year on year
With the yield predictor tool you can now compare how this prediction compares to your previous prediction, and you can easily see the total predicted weight for the vineyard as well as the predicted yield for each block. In the previous prediction you were using average weights, now you are using actual weights from this year with a multiplier – does it look too high or too low? If things are looking exceedingly good this year, then maybe do another yield prediction with a weight multiplier of 2 – for example the harvest of 2019 in the UK people were seeing weight multipliers of 2 or more from veraison to harvest, but that was of course a very unusually prolific year. Also there can be considerable variation between different varietals when it comes to the weight multiplier, so if you do have past years data then it’s best to customise the weight multipliers for each block based on the history at your site.
Fourth prediction: Include last minute losses due to disease/pest pressures
Yield prediction calculation including potential loss from Botrytis
To see how things are progressing you can go out and weigh more bunches 4 weeks after veraison. How have the bunches developed? How much bigger will they get by harvest?
Of course there can be unforeseen issues with disease pressure in the final weeks. This is easily accounted for in the yield predictor by adding in what % of the crop you have lost due to the problem. This will update your yield prediction estimates in the final stages of your yield prediction journey.
Weigh bunches at harvest
It is key to measure the average bunch weight at harvest and enter that into Sectormentor too. You can either go and pick random bunches on the morning of harvesting a particular block, or you can harvest the sample bays from each block before harvesting the rest of each block (you have already counted the number of bunches for sample bays so you can easily work out the average bunch weight by weighing all the bunches that are harvested from that bay).
This number of average bunch weight at harvest is vital so that in future years you can figure out what the actual veraison-harvest weight multiplier is for each block in your vineyard. It also helps to get a very good idea of your average harvest bunch weight for a particular block over many years, so that those early predictions that rely on this weight become more and more accurate.
It’s an art and a science..
Yield estimation is a real art. The more in tune you are with your vineyard and the more you know your vines, the easier it will become – if you are consistently getting within 15% of the actual yield then that is considered good in cool climates. However, if you are very committed and refine the details, meticulously measuring bunch weights at lag/veraison and harvest each year, getting clear on your weight multipliers for each block, then many vineyard managers believe you should be able to get within 5% accuracy every time.
We’re working with vineyards on exploring soil health monitoring and the value it can bring to the enterprise. Bee Tree Vineyard in West Sussex is owned and run by Vine-Works, who also provide a suite of management services from planting through to harvest for vineyards across the UK. They use their 1.5 hectare site of vines to trial new management approaches which they might then apply to vineyards they manage for their clients.
Healthy soil should be brimming with biological life and full of carbon sequestered by a diverse range of plants. Plants exude sugars into the soil through their roots during their vegetative growth, feeding micro-organisms in the soil, which can in turn unlock nutrients for plants to take up when they need them. Micro-organisms also secrete glues and slimes which hold the soil structure together, forming aggregates – the basis of healthy soil. This aggregated structure allows water and air to easily percolate around and through it, so the soil will be able to hold more water deep down in its profile for when plants really need it, as well as remain aerobic.
Synthetic and chemical inputs such as herbicides and nitrogen fertiliser, as well as turning the soil, can disrupt plant root-soil interactions and hence disrupt feeding the vital soil biology. Vine-Works have been investigating how to reduce reliance on inputs and manage soil biology positively at Bee Tree Vineyard. The Vine-Works team have replaced undervine herbicide usage with a mechanical undervine weeder which they have found very effective. They’re also trying a new type of chicken manure compost pellet made by ‘Cloud-Agro’ to further feed the life in the soil.
Improving soil biology by increasing plant and root diversity is one of the first steps on the journey to reducing inputs in a vineyard. Vine-Works have been trialling different mixes of cover crops with diverse root systems in the rows in between vines to improve soil biology. When we visited Bee Tree Vineyard we chose sample sites to assess soil health based on the different cover crops to see how these have affected soil structure and biology. Bee Tree are one of our first vineyards to start recording soil health observations using Sectormentor for Vines. These first tests form their ‘soil health baseline’ so they can understand where their soil is at now and where they want to go in the future.
By comparing between different rows that were next to each other but had been managed slightly differently we were already able to see some stark differences in how the soil was structured and stored water. One row where the cover crop sewed this Spring had never taken performed significantly worse than the neighbouring row with a cover crop that was well established from the year before. It has already enabled Vine-Works to change some of their management strategy, in that they will now plant their cover in Autumn to give it plenty of chance to establish and reduce the risk of bare soil!
We wanted to talk you through exactly what we did, the different tests and what they mean:
Our first sample site was a block of Cabernet Blanc with a deep rooting cover crop planted in between the rows, including radish, chicory and cocksfoot grass in the mix. These plant species are good at getting roots down into the soil, breaking it up, and bringing nutrients up from below. We saved the exact location of the sample site using GPS coordinates in the Sectormentor for Vines app. This means the team can go back to the same place in 6 months or a year and test again to see how things have changed.
First we dug out a spade’s width soil pit and visually assessed the soil structure (VESS test) for both under the vines and in the row. Under the vines the soil structure was quite blocky, but it did break down relatively easily in one hand. It was slightly better in the row under the cover crop, where the first inch of soil in the rooting area was nicely aggregated, but the clay got harder and blockier as we moved down the profile.
Next we did a Slake test, submerging 1p sized bits of the soil in a sieve in water and observing how quickly it broke down. The soil under the cover crops did well in the slake test, only losing around 20% of its structure. If the soil is alive with micro-organisms the structure will be held together with glues and slimes they secrete, and so it will not break down so much in water. If the soil is held together by compaction, it will break down easily. This test gives you an idea for biological life in the soil and how much soil could be running off your vineyard in heavy rain.
Finally we did Infiltration Rate test by knocking a 150mm tube into the ground and pouring in an inch of water. This gives an idea for how easily water can percolate into the ground and be stored there, instead of running off and into water courses. The infiltration rate was very slow under the vines, suggesting water can easily run off from this area. However it infiltrated faster into the cover crop, which is good news as it suggests rain water will be better stored in the soil for drier periods when the plants need it. The Vine-Works team used the Sectormentor for Vines app to record all these results so they can start to compare them with other sample sites across the vineyard.
Next we headed next to a block of Pinot Noir with a different cover crop in between the vines, a mix including clover and trefoil. Clover is a legume and has the capacity to fix nitrogen in the soil on nodules on its roots. Here we found the cover crop had not established as well as the deeper rooting cover we previously tested.
There was much more bare soil in the row, which means there are no living roots feeding the soil in these places and the soil is more at risk of running off with heavy rain. The Vine-Works team recorded the % of bare soil, broadleaves, grasses and undesirables in the Sectormentor for Vines app so they can assess how well they are improving plant diversity. We dug out a soil block and instantly noticed how much drier and blockier it was than the soil at the first sample site. It was harder to break down with one hand, breaking up into angular blocks. So, it didn’t score as well on the VESS test as the first site!
Now onto the slake test, placing 1p pieces of soil into water; due to the high clay content in the soil it held together relatively well, but still broke down more than the first sample site, losing more than 30% of its structure, showing that there is less biological life in this soil.
We really struggled to get the infiltration rate tube into the ground, showing compaction issues, which were corroborated by the very slow infiltration rate both in the row and under the vines. The Vine-Works team recorded all the soil test results and the GPS location of the pinot noir sample in the Sectormentor for Vines app; in the future they will be able to see the sample site on the map and get back to it easily to test again and see if things have improved.
At the second sample site the lack of establishment of the cover crop had clearly affected the soil health in that part of the vineyard, whereas at the first sample site the soil biology had started to get going. It was exciting to see so clearly how the different cover crops had affected soil health, allowing the Vine-Works team to understand what’s happening below ground and make decisions on how to move forward with improving soil health. The team went onto sample another site in the Pinot Noir block which had the deep rooting cover crop and did an ‘under the hedge’ test to get an idea for how good the soil could be. For an ‘under the hedge’ test you find a completely undisturbed spot of soil, by a hedge or in a woodland, which has not had any intervention. This will give you an idea for what the soil biology and structure could be like!
“I found the soil health tests very interesting, it’s changing how I think about vineyard management.” – Matt, Vine-Works
So, what’s next on the soil health journey for Vine-Works & Bee Tree? Soil monitoring regularly will help them understand the impact of different vineyard management techniques on their soil health. After varying success at establishing cover crops this season they plan to sow their cover crops this year just after harvest (Oct/Nov) rather than in Spring. From the VESS, infiltration rate and slake tests they could easily see just how negative the impact of bare soil from a poorly established cover crop can be, so by sewing in Autumn it will guarantee plenty of water to get the cover crop established. It was also clear that undervine cultivation was greatly slowing the infiltration time under the vines, so they are much more likely to get serious run off and leaching of nutrients from this soil. They have plans to try alpine plants under the vines next season, which will provide perennial cover and living roots in the soil all year round. These are hardy plants which do not need reseeding, so it’s an exciting trial!
In the autumn the team will be heading out to do earthworm counts, as it was too dry to do them when we visited this time. Earthworms are one of the best indicators of biological life in the soil, as if they are plentiful and present and active, many of the microorganisms will be too.
Find out how Sectormentor for Vines helps you monitor soil health in your vineyard & learn how your soil is changing. Contact us if you have questions!
We’ve got fanmapstic news! GPS mapping for sample points on Sectormentor for Vines is now available for iPhone and Android! This makes it really easy to come back to the same sample sites when monitoring your vines.
What does this mean?
For every sample site a GPS location can be saved using the Sectormentor for Vines app and viewed on the map. Using the map on your phone app, you can see your current location and where each sample site is, making it easier to follow the map on your phone to the bay that you need to monitor. Plus if you are already in the map view, you can just click on the pin and it will allow you to start entering information for that sample bay, all from the map view.
Why does this matter?
Coming back to the same sample sites when monitoring information on your vines is important, it helps you to maintain more reliable results year on year. With GPS you can locate your samples sites and contactless tags much more easily, as you can use the map to see the closest sample site around you and where to go next.
It’s also very helpful for people who don’t know the vineyard as well, helping them find their way around and quickly know where they should go, for example to do a flower count, or which bays they need to record pruning weights in.
Got any questions about GPS and using Sectormentor for Vines to monitor your vineyard? Contact us!