The mystery of soils and wines, part 5


The mystery of soils and wines, part 5

Two vineyards 100 m apart. One treated with herbicide, the other allowed to grow a cover crop.

So where are we up to with soils and wines?

We began by exploring the ideas of minerality, and how soils might be having a direct effect on wine quality, even though science seems to indicate that soils impact upon wines rather indirectly. We explored the idea that what is perceived as minerality might actually be a result of ‘reduction’. And then we looked at the way that the root environment affects above-ground growth through hormone signalling.

Now let’s think about the issue of soil biology, and how this could be affecting the vine.

‘The extent, health, and physical and chemical environment of the roots must be a major key to the best ripening and terroir expression.’

John Gladstones, Wine, terroir and climate change (Wakefield Press, 2011).

Vine roots respond to the conditions of the soils they are growing in. First of all, a large permanent framework of roots is established, followed by a network of finer lateral roots, and finally even finer tertiary roots which are vital for uptake of water and nutrients. Nutrient uptake by the roots can be both passive and active. As the vine takes up water, it will usually take up whatever is dissolved in that water. But if it lacks specific nutrients, it can take them up actively, if they are present in the soil. There are some situations where the vine is fooled, though, by mineral ions that look quite similar, such that a deficiency of one can occur when there’s an abundance of another. And, for example, in soils with a lot of limestone, chlorosis can be a problem. This is because in limestone-rich soils, vines find it very difficult to take up iron, which is needed for photosynthesis, as a vital component of the green-coloured chorophyll pigment. As a result, the leaves turn a yellow colour and are diminished in their ability to carry out photosynthesis, the process of transforming light into energy.

A special layer of material called the Casparian strip surrounds the root endodermis, the layer of cells that circle the vascular tissue. This strip contains suberin, a waxy, rubbery material that is impermeable to water. Thus water and solutes entering the roots have to pass through plasmodesmata (pores in the cell walls) and therefore through the cytoplasm of root cells, before they can be transmitted to the rest of the plant. This gives the vine a level of control to what is taken up. The plasmodesmata are significant because they allow direct communication between the cytoplasm of adjacent plant cells, through the otherwise rigid cellulose cell walls.

How do vine roots take nutrients from the soil? One of the key concepts here is cation exchange. Roots are able to exchange hydrogen ions, which they pump out, for the cations attached to the negatively charged soil particles such as clay and humus. Clay often carries a negative charged, whereas humus – decayed organic material – can carry both negative and positive charges, and so can hold both cations and anions. Cation exchange capacity (CEC) refers to the number of positive ions (such as calcium, magnesium, iron and the nitrogen-containing ammonium ion) that the soils can hold. When clay and humus have a negative electrical charge they are able to hold onto positively charged ions. Generally speaking, CEC correlates positively with soil fertility, because it determines how many plant nutrients the soils can hang on to. Soil pH also affects CEC: more acid soils (lower pH) have a lower CEC than more alkaline soils (high pH). One way to increase CEC is to increase the organic content of soils. This has the benefit of both increasing CEC, and thus fertility, and also increasing soil texture. Without organic material or clay, soils find it hard to retain nutrients. For example an excessively sandy or gravelly soil will allow mineral ions to be rapidly leached from the soil by rainfall.

So where do the mineral ions (nutrients) come from in the first place? It is not really from the bedrock, which would be the intuitive assumption on many. Some mineral ions might be bedrock-derived, but these would largely be in the subsoil. Low levels can come from rain, and some can come from the weathering of larger soil particles such as stones and rocks, but the bulk of soil nutrition will come from decaying organic material.

To get a better handle on this I spoke with Tim Carlisle, who has studied soil science, but also has a deep understanding of wine from his current employment as a wine merchant. ‘We need to then look at the microbial activity in soil,’ he states. ‘This affects the speed and ability of soil to break down organic matter into mineral ions that can be used by plants – and also aids the uptake of ions by plants. Because of this, no discussion about soil should exclude them, because whatever the terroir is, the level of microbial activity is an important and always overlooked element.’

Carlisle points out that there are many factors that influence this microbial activity, but primarily water, food and oxygen. ‘Oxygen is more available in a loose uncompacted soil,’ he says. ‘A soil that is overly compacted has little oxygen and so little microbial activity – the same is true of a waterlogged soil – which Is one reason why porous bedrock and/or slopes are important, not just because of vine stress but because the microflora and fauna don’t get drowned.’ The term microflora refers to the bacteria and fungi in the soil. Their existence also governs the level of microfauna, which refers to soil organisms ranging from single-celled protista to small arthropods and insects, through to nematodes and earthworms.

‘The food they need is organic matter. If you visited a conventional agriculture wheat field you’d find that there was very little organic matter in the soil, and as a result very little microbial activity, which is further diminished by crop spraying – hence the vicious cycle of needing to use tons of fertiliser.’

During his studies of soil science, Carlisle looked at the effect of fungicides, herbicides and insecticides on the soil microbes. He did this two different ways. First, he took microbes from the soil, grew them in culture, and then studies the effects of dilute agrochemicals on their growth. ‘What I found in this was that fungicides over herbicides and insecticides kill off not just fungi (which includes yeasts and moulds),’ says Carlisle, ‘but also a high proportion of bacteria, and actinomycetes (I didn’t do anything with algae), but also that herbicides and insecticides also killed off a proportion of all types of microbe, and restricted growth of others.

He also studied the overall microbial activity in the soil. ‘What this showed up was that untreated soil was healthier than anything with any kind of treatment, including one that was sprayed with fertiliser,’ reports Carlisle. ‘If you think about it, minerals are essentially the excretion of microbes. Too much excretion to soil will poison them and so spraying with fertiliser actually caused a check in microbial activity – it continued but at a lesser rate.’ He adds, ‘the thing that was by far the most interesting from a viticulture perspective was that one of the samples was sprayed with copper sulfate, which is permitted in organic viticulture. This sample was the one in which microbial activity was reduced by the most.’

This raises interesting questions. Clearly, soil life is important. And this soil life can be affected by vineyard treatments. It poses a problem for organics and biodynamics: while these approaches aim to encourage soil life, the fact that they need to rely on copper – a traditional but toxic remedy for fungal disease – is at odds with this approach. But then conventional remedies, such as the use of systemic fungicides, are also problematic.

8 Comments on The mystery of soils and wines, part 5
wine journalist and flavour obsessive

8 thoughts on “The mystery of soils and wines, part 5

  1. We’re starting to get into some interesting stuff now in this series.

    I wasn’t surprised that Copper Sulphate had the most detrimental effect on microbial life but I also wonder about sulphur.

    I’d be interested to know if people have looked at the effect on microbial life when glyphosate is used in the vineyard.

    I’m also thinking that the type of ground cover you have is very important. People focus pretty much on the nitrogen giving properties of cover crops but what if different ground cover can give different flavours in the wine?

  2. Hi Jon,

    I do somewhere have a full version of the data – the analysis at the time is pretty rough (the practical work over ran by about 2 months which essentially meant i wrote the results and analysed them at the time in 24 caffein fueled hours to hit a graduation deadline…..

    Without looking I’m 95% certain I’ve got some Glyphosate date too. Interestingly I’m on the way back from a couple of days in Bordeaux and was at Chateau Laroze last night for dinner. Guy Meslin was telling me that they converted to Biodynamics in the 1990’s as one of the first Cru Classe’ estates to do so. However his claim was (and I’d have to take a bit of a pinch of salt with it) that he got a copper sulphate build up such to the extent that his vines shut down – he stopped Biodynamics (he says) on this basis. Personally it sounds to me like he was perhaps going overboard on its use anyway – but he also has drainage issues being at the bottom of the slope in St Emilion as you head towards the edge of Pomerol (ish). I suspect his build up is partly as drainage issue although he has now installed drainage in the vineyards and has increased planting density.

  3. First of all, congrats and thanks for such an interesting series of posts, and to Tim Carlisle for his research. Now, here’s the 2p from a guy from Rías Baixas: copper is indeed an issue in organic/BD/younameit wine growing, but its use can be drastically reduced by using alternatives to sulphate (hydroxide, for example)and adding plant extracts which have a synergistic effect. There’s a bunch of people in Ribeiro and elsewhere (among them the guys at Coto de Gomariz and Bernardo Estévez []) who are proving that it is possible to use copper in low doses even in such a damp place.
    Keep up the good work!

  4. Thank you I enjoyed reading this article; It is info-dense and in-depth. Photosynthesis is oversimplified though. Light is not “converted to energy” it already is energy. Maybe better stated as the plants action of capturing light energy, carbon dioxide, & water, and converting it to chemical energy in the form of carbohydrate. One major effect that soil structure has on wine quality is the presence or absence of clay. Clay, with its water holding capacity will retain water, regardless of how well drained the sub-soil is. Evaporation will dry soils only to +-6″ below the surface. So the water held in the clay is only available to plant roots that can actively pull the water out from between the fine clay platelets. The surface tension of water prevents the force of gravity from pulling the water out of the clay structure.
    The grapevine is fairly straight forward in its objectives; Second to staying alive, its priority is to reproduce. Without locomotion, the only option to relyably create recombinant diversity is to develop viable seeds, and make the seeds attractive to other organisms with locomotion. Methoxypyrazine is synthesized by the grape vine early in the season to make grapes taste bad to birds and animals (and humans) while the seeds are still developing and not yet viable. Similar in purpose to the acids in grapes.
    The problem for grapevines on clay is that clay soils do not dry out soon enough in the growing season for the vine to start respiring its Methoxypyrazine. This isn’t as big a problem for the grape vine as it is for vintners. If the desired result is a wine that is balanced and free of vegetal characters, the vines need to start respiring acid and Methoxypyrazine ( or Rotundone in the case of Syrah) early. Slight water stress around the time of verasion triggers the vine to start getting the fruit attractive. Along with accumulating sugar and changing the color of the fruit, the grapevine starts to actively respire the bad flavors. Of course the vintner can just wait until the vegetal flavors are no longer perceivable, but by then the fruits other chemical parameters are out of balance.
    This highlights the importance of the correct soil type for the chosen cultivar.
    Cabernet sauvignon with its Sauvignon parentage, has a propensity to produce a lot of Methoxypyrazine, characterized as a Bell pepper-grassy flavor. While soil CEC, and micro flora are important influences on grape vine heath and productivity, field capacity or the amount of water held in the root-zone may have a more profound affect on wine quality.

  5. Jamie, thanks for this series of extremely interesting articles. I’ve learned lots of theory from them 🙂
    The only thing that I can add to the discussion is just to say (and I’m sure that all organic or biodynamic grapegrowers would say the same thing) is that to me it’s already intuitively obvious that healthy living soil is essential to the production of quality grapes and terroir-expressing wine. I suppose that chemical-using grapegrowers thinking of going organic need the comfort provided by rigorous “scientific” and “authoritative” studies that confirm the obvious!!!

  6. Good stuff Jamie. Vines are fabulous at maintaining their own balance in the face of change. It is essential to remember that what we take away each year needs to be replaced. Essentially light and water give us what we need with a little loss of micro nutrients. If the soil pH is out of balance then problems will arise. Key word is aways balance. Some soils have it and others may be too acid and others may be too alkaline. If pH is OK then the key is the thermal mass of that soil and its water holding/draining ability. Wine producers in my region, the Mornington Peninsula, Victoria, Australia have been using data loggers for the past 7 years to gather data on what makes our individual sites special. I suspect we are just starting to get somewhere. One thing we agree on, data is good and is better than being anecdotal. I suspect that it will take at least another 2 years of data gathering to have enough data to gain a meaningful understanding. Then I guess it will all get complicated by climate change. Sigh

  7. Hi Jamie – thanks for this valuable series. If you ever have time (ha!) and wld be interested, you might like to get in touch with David Lefebvre, oenologist and chemist, who’s been working a lot on minerality. He lectures and writes extensively on the subject, including at a recent course at the Lycée Viticole in Rouffach (Alsace) that I attended along with whole lot of Alsace wine makers, many of whom you know. There’s an interview with him published in a recentish Le Rouge et Le Blanc. I think you’d have loads to talk about together.

  8. very nice article, thanks for that deeply research only a view people in the world are willing to go that deep in to terroir and soil but is the only way of understanding things.
    Sorry for my english but it is not my mother language so i hope you understand.
    I am a biodynamic winemaker who believes in his work. But i scrutinise every work i do and try to understand it deeply and fully.

    three things i would like to refere.
    1. I really believe the the Casparian strip is the most importend thing for the plants nutrients. in my opinion the funktion of the deep going down root is only the water and in healthy Environment this is naturally very low on nutrients.

    2. i don’t believe in stress for the wines. nature on it self is enough stress (climate, water, light) so we as winemakers should try to avoid stress for the plants. so you will get the best grapes.

    3. Copper: it sure that biodynamics and organics winemakers have to get rid of copper and there are some alternatives we will see in the next years.
    but on thing we have to keep in mind the high copper content of the soil in our vineyard is coming in the times bevor the 60th at this time it was usually to use up to 30 kg of Copper/ha. (today only at strawberries you are allowed to use that much copper)
    today conventional winemakers in austria can use 6kg of cooper/ha and organic/biodynamic can use only 3kg/ha.
    most of the conventional winemakers are using around 3kg which is the maximum of the organics.
    We manage with tunnelsprayers to come down with copper to 1-1,5 kg /ha this is about 0,15 grammes per square meter.
    If you have a copper roof gutter you are far above this. or trie to cut 0,15 grams of electric wire (you can even not hold it or see it it is so small) an put it on the soil of on square meter.

    What is interesting the copper task force of the EU found out that copper has a very toxic reaction on soil life in the lab. But the found out that copper is on the field far less toxic, it is significantly proven that copper in the field is about the factor 6 less agressive on soil life! So I think there has to be still much more research be done!

    So I hope that in the long term organic and biodynamic winemaker can get rid of copper. But believe me Glyphosate and the systemic Fungizides are far more of a problem for the soil life!

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