Understanding The Terroir of Burgundy part 4.4: Erosion: a challenge to the authenticity of terroir

Erosion Vosne wider implications

Our best understanding of soils of the Côte de Nuits:

In trying to grasp the relationship of the wines made soil from particular crus, many writers, myself included, have come to many fundamentally incorrect conclusions regarding terroir. My version could be summarized into this:

I believed that chemical and mechanical weathering of the limestone bedding naturally created soil types that were dictated by their position on the slope. Highest on the slope, the compact limestone soils were produced by the simultaneous production of clay and the erosion of clay. Lower on the slope, where transported clay enriched the otherwise arid, colluvial soils, I believed that if farmed carefully, clay production could remain in a relative of a state equilibrium with clay erosion. While, it most of these vineyards may not absolutely been in their natural state as when the Romans arrived, of many mid-slope Burgundy vineyards, I felt were relatively authentic in their terroir.  

A challenge to the authenticity of terroir:

Vosne-Romanée Les Damaudes, sitting upon the upper-most slope, with a 12% grade had equal parts clay and gravel in 2004. This is despite already having lost 54mm depth of clay sized particle since 1952. In the foreground, Vosne Malconsorts is allowed to grow it's grass in June of 2012. photo: googlemaps
Vosne-Romanée Les Damaudes, sitting upon the upper-most slope, with a 12% grade had equal parts clay and gravel in 2004. This is despite already having lost 54mm depth of clay-sized particle since 1952. In the foreground, Vosne Malconsorts is allowed to grow its grass in June of 2012. photo: googlemaps

The 2008 study on the changes to soil composition following a heavy rain event by Quiquerez, Brenot, Garcia, Petit, and Catena, presents, in my view, far greater implications than the study’s more simple intent of establishing hard erosional data following heavy rain events.

The study’s plot site, high up on the hillside, with a long, 12% grade, would challenge the perception that upper-slope, Burgundian soils naturally carry low percentages of clay or silt. This vineyard, with its 40% clay content, at the onset of the study, is doubly surprising, given that the data showed these materials exhibited a high erosional rate out of the plot area. What the soil recording reveal natural soil composition of this hillside originally contained far more clay than we could have ever expected based on the compact gravel “soil” condition of even the best of the upper slope vineyards today.

This study not only gives us a prophetic view of this vineyard’s future soil but also clearly illuminated a much more fertile soil in the past. Just as this vineyard once had an exceptionally high clay content, there is every reason to believe this was also true across the breadth of Burgundy vineyards, indicating a very different erosional story played out regarding the ‘arid’ soils of elite mid-slope vineyards. This information directly challenges our perception of the authenticity of the terroir within many of today’s Burgundy vineyards. 

What the study of this vineyard tells us is that, at least on this site, there has been a relatively tight erosional timeline, with much of the damage occurring over the past half-century. Additionally, the erosion is projected to finish its ‘third act’ in Les Damaudes over the next 25 years, at which point it will have a classic Burgundian compact limestone soil.  While it would appear that mechanized farming as the most erosive in this vineyard’s largely unreported history, we know that there was massive erosion in other vineyards over the centuries. The remaining question is: What about the historical farming of this vineyard allowed its clay to remain in this parcel of Les Damaudes?

*This article is based on the findings a pair of studies chronicled in Part 4.3, and centers upon the upper hillside plot of Vosne-Romanée’s village cru of Les Damaudes.

Why is this study so important to our understanding of Burgundy?

It has slowly become apparent that the problem in talking about the terroir of Burgundy is this: We really don’t know what the wines of Burgundy might have naturally been, had men had both the knowledge and forethought to do what it would take to preserve these vineyards centuries ago. However, a study like this (click here) gives us the ability to hypothetically see both where this vineyard is going, and what it might have been like before man caused so much erosion upon the hillsides. We were lucky that the researchers chose this particular vineyard at the top of VosneRomanée for their study. Les Damaudes is a steep hillside vineyard (in the most revered of villages) that is only midway through its journey of erosional destruction.  A study of a vineyard from any of the other lesser appellations could easily be dismissed as not being applicable to les grands villages de Bourgogne. But with a vineyard within VosneRomanée, there is no doubt as to the applicability of the information, as this vineyard is in the immediate vicinity of some of the greatest vineyards in the world, including La Tache and Romanée-Conti.

soil projection
The projected future soil composition of Les Damaudes over the next 5 storms (roughly 25 years) Click to enlarge.

It has become increasingly clear through the research in preparing this series of articles, that vineyards like Ruchottes-Chambertin have been so seriously degraded by the techniques of the farming employed there, that the terroir we talk about today is one that wears immense repercussions of the farming practices of the past centuries. However, it seemed plausible, that the upper slopes could naturally have developed a compact limestone soil, (one that is 85 to 90% crushed limestone and only 10 to 15 % clay). But these studies re-orient our thinking, forcing us to realize that this is not a soil type that is natural to Burgundy. Because of that, it is not a terroir that is natural to Burgundy.

It is not to say that these vineyards, with their degraded soils, do not produce beautiful or interesting wines, but we must realize that this is a vineyard condition that has been inflicted by man. In the truest sense, Burgundy now has a terroir that has been drastically altered, metamorphosed by the actions of man.

Note: at the bottom of this article I discuss data gaps and the certain information the study might have provided which would have been key to a more complete understanding of the soil of Vosne Les Damaudes. 

2004: Establishing a soil base-line

Although the changes to the soil makeup after the 2004 storm were covered in-depth the latter half of Part 4.3, it is the basis for projecting what the soil make up was in 1952, so it bears a brief retelling now.

Click to enlarge. Adapted from the paper "Soil degradation caused by a high-intensity rainfall event : implications for medium-term soil sustainability in Burgundian vineyards" Quiquerez/Brenot/Garcia/Petit, Catena 73, 2008
Click to enlarge. Adapted from the paper “Soil degradation caused by a high-intensity rainfall event: implications for medium-term soil sustainability in Burgundian vineyards” Quiquerez/Brenot/Garcia/Petit, Catena 73, 2008

In June of 2004, a storm, which was unusually large for Burgundy, dropped 40 mm of water on Vosne Romanee over a 24 hour period. The effects of that storm were studied, and the researchers determined that the vineyard plot had irrevocably lost between 1.8 mm and 4 mm soil due to erosion, a vast majority of which were very fine particles under 63 μm in size.  The material lost was clay and silt since erosion most efficiently targets these tiny particles. (1)

To the right is a graphic I adapted from the study to show the grain size distribution of the soil after the 2004 storm. Each rectangle represents a range of particle size. I also included the before level of clay and silt sized particles to illustrate the loss of those materials, which was shown as 25% in a graph in the study.

 

1952: the soil content of the past

Given the study’s data, we can extrapolate, at least conceptually, what the clay content on these slopes the vineyard was planted in 1952.(2)  Starting with the fact 2004 the hillside contained roughly equal parts clay and gravel at 40+% each; the balance being sand, that we can add 54 mm more super-fine material (smaller than 63 μm) that it did in 2004.  If we assume that past soil loss rates were similar to that of the 2004 storm, we can postulate how much clay would have been present in 1952.  This figure would be much easier to arrive at if the researchers had given us the soil depth, which would allow us to estimate the volume of gravel (colluvium) and allow us a much more accurate estimate, but that information was not within the scope of the study.

Click to enlarge. Adapted from the paper "Soil degradation caused by a high-intensity rainfall event : implications for medium-term soil sustainability in Burgundian vineyards" Quiquerez/Brenot/Garcia/Petit, Catena 73, 2008
Click to enlarge. Adapted from the paper “Soil degradation caused by a high-intensity rainfall event: implications for medium-term soil sustainability in Burgundian vineyards” Quiquerez/Brenot/Garcia/Petit, Catena 73, 2008

The soil loss projections of the next five large storms, predicts that erosion will remove up to 20 mm in-depth in places. The lost material, it is expected would continue to consist of primarily be smaller than 63 μm in size. 

However, would it not be logical assume soil losses of previous storms were similar to that of the 2004 storm? If so, it would not be unreasonable to apply the projected soil loss, in order to estimate the vineyards clay percentage in the past.  If these big storms (of 40+mm rainfall per event) happen every 5 or so years, we can estimate that thirty years ago this same hillside may have had as much as a 70% clay content. How much clay existed before the plot was planted in 1952 can not readily be determined without establishing a rough estimate of the volume of gravel in the vineyard, but it is likely that the vineyard, may have had clay content 85%.  Such a high percentage suggests that either this plot was either not farmed before it was planted in 1952, or was farmed quite differently in the past than it is now. 

In Retrospect

We should not have been surprised that the soils of Burgundy are not as nature created them. We should have suspected something was amiss long ago because the soil type in Burgundy today is one of an arid climate. France, and the surrounding Burgundian countryside, however, do not have an arid climate at all. Rather the climate is classified as semi-continental, where rain is frequent and happens virtually year around. These soils would naturally have at least some petrogenetic development, which it is doubtful that any vineyard in the Côte d’Or does. We were told and simply wanted to believe that the wines of Burgundy are naturally and uniquely sparse of nutrients and clay. Additionally, we have not wanted to believe that, in the course of making these great wines, man has precipitously hastened the decline of the greatest vineyards of the world, though poor farming decisions that have been made throughout the centuries. This has never been truer since the organization of vineyards for the mechanization of farming.


 

Gaps in the data: deficiencies in quantification

As transformative as this study is to our understanding of the wines of Burgundy, the paper, unfortunately, omits some fairly important information. First and foremost, it is unclear how the samples for the data were collected, and secondly how well the data actually represents the soil of the slope in the root zone. The report does say that the soil of the vineyard was homogeneous in its makeup, and no petrogenetic development was observed; meaning the entire vineyard was the same, with no observable generation of new soil. This indicates that what little organic deterioration may develop was washed away by erosion, and no soil horizons (layering) could develop  Lack of soil development and soil horizons would be caused the dual soil disruptions created by regular tilling and erosion.

However, the problem lies in the word “homogeneous”. Even if at some point the soil was homogeneous from topsoil to bedrock, erosional changes to the soils would primarily affect only the material nearest to the surface, and then most acutely in the rill affected inter-rows. Now, even after one storm, the soil is no longer homogeneous in its makeup, because the soil at a certain (unknown) depth would contain more clay and silt sized particles than the topsoil. Now there would be two soil types.

Because of this, we must assume that the researchers collected a shallow soil collection for the sample in order to determine particle size.(3)  Quantifying the depth of this sample is critical, was this a  sample from the first 25mm (1 inch) or 50mm  (2 inches) or from deeper, say 200 mm (8 inches) of depth which is the deepest that most tilling reaches? Further, when the samples were collected: ie before or after anthropogenic resupply of the sediment was returned to the slope, and before or after the soil was tilled, are both important factors in understanding the distribution of soil.  Additionally, knowledge samples at various depths of the sample would be instructive as the effective depth of the erosional change. This is ever truer after workers had returned the sediment to the hillside, and tilled back into the soil.

Root development through soil
The root zone on a hillside vineyard is often restricted to no more than 300mm (12in) to 460mm (18in) represented by the brown strip in the graphic above.  Original graphic of unknown origin.

It would appear that the study only represents changes to the surface soil: those that would most be affected by erosion, and anthropogenic resupply of the sediment to the hillside. it is possible but less likely, that the soil sample may have been taken down to a 200mm depth (8in), which is the standard reach of a plow shear. But even if samples were taken from the 200mm depth, that is only 2/3s of the minimum depth required by a vine for its root zone.

Despite questions and any doubts these numerical omissions might create regarding the validity of the numbers and projections from the study, the value of this information far exceeds reaches far into the black hole of understanding that existed before. For this reason, I accept these numbers and build in a fairly wide mental fudge-factor when considering the above.

 

 

Puligny Folatieres after a rain
A tractor moves on the road between Paul Pernot’s “Clos des Folatières” and Les Clavillons in Puligny-Montrachet photo source: googlemaps

 

Musigny anthopogenic resupply
“Anthropogenic resupply” of redepositing the sediment back upslope is now done with heavy machinery at Comte de Vogüé. photo: Steen Öhman
Musigny anthopogenic resupply 2
Heavy machinery at Comte de Vogüé. Given a major cause of erosion is compression, it’s hard to imagine this is really helping the situation much. photo: Steen Öhman

*Special thanks to Steen Ohman, sleuth, and vineyard historian who writes the excellent winehog.org, for providing me with the 1827 cadastre Map show above.

 


(1) The variance between the 1.8mm figure and the 4mm figure was not explained, but it is likely that lower sections of the vineyard, which were subject to a higher volume of rainwater runoff, and had developed rill erosion, were subject to greater levels of erosional loss.

(2) While the study lumps both clay and silt into a grouping of material by size under 63 μm, according to Wikipedia, as well as other sources, say that silt is primarily made up of the parent materials feldspar or quartz. Feldspar is prone to chemical erosion, just as is limestone, both of which metamorphose into clay (phyllosilicate minerals + water and air), while quartz will not erode due the same contact with the carbonic acid in rainwater.  Although granite (the major source of quartz-silt) is common in the areas surrounding the Cote, like in Beaujolais, it is not found near the surface in the immediate area. Although silt has been washed onto the Cotes by alluvial action and transported to the soils of the Cote by wind erosion, I have to assume that silt-sized quartz fragments are a very small minority in the area’s soil makeup. For that reason, I often refer to the study’s grouping of material under 63 μm, simply as clay. Clay, of course, is actually smaller than silt. Although the size definition varies between disciplines 1–5 μm, the metamorphological change that occurs upon clay is the ultimately defines clay, not its size.  * an underlying reason that I identify this material may also be that — no wine writer has ever attributed any of Burgundy’s success to silt. Am I cowering in conformity?

 

(3) How else could one explain a 15% change in a clay content?  The planting bed must be at least 30cm  (12 inches) for vines to be viable. Most vineyards have this with a much lower clay content, often to 30% less. If we were to use 30cm depth as a baseline, it stands to reason that the depth is likely 30% more than 30cm, being at a minimum 40cm of soil over the base rock though there is likely more. So, if the soil is 400mm deep, and 240mm of that are clay minerals, a 4mm decrease in the clay represents only a 1.7% decrease in clay content in the soil.

 

 

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Understanding the Terroir of Burgundy Part 4.3 Erosion and Rills: Studies in Vosne-Romanée and Monthélie

Erosion in Vosne Romanee

In the water’s path

Erosion comes in two forms: the seen and the unseen.

Rill erosion is the most obvious form of erosion and typically occurs in heavier downpours of more than 30 mm (1.2 inches) over a 24 hour period. They begin in spots where soil aggregates are weakened, and will collapse with weight and friction of the water above it, forming the aqueduct-like channels into which the runoff will funnel. Rills often generate in flow zones,  gathers in the depressions between rows. Here water can consolidate, growing in volume and velocity as moves with increasing rapidity down the hillside. With the water growing in mass and speed, larger and larger soil particles are pulled with it, releasing from both the bottom and sides of the rill, developing their typically U-shaped trough. As rills go unrepaired, they can grow substantially,  that can be difficult to control, if measures are not already in place to prevent them.

Sheet erosion (aka surface erosion) is a precursor to, and happens simultaneously with, rill erosion. In this case, rainwater runoff moves in sheets across the surface of the vineyard, but between and through the vines in places where rills won’t, or have not yet, formed. Surface runoff has a less concentrated volume of water than the runoff that travels through rills, so it yields a lower speeds and less velocity. Because of this limited velocity, the water of surface runoff is capable of carrying particles with a lower suspension velocity than rills are capable. These may include sands, but unless the downpour was heavy, would primarily include clays and silts. In less intense storms (< 20mm) surface runoff can cause sheet erosion, but these actions are considered slightly erosive, typically transporting finer materials in weak aggregates. From year to year, soil loss to sheet erosion goes largely unnoticed as the topsoil loss directly beneath the vines disappears down the hillside forever.

  • For an explanation of erosional factors and concepts click here for part 4.2
  • For history of erosion and vineyard restoration in Burgundy click here for Part 4.1
  • For the history of erosion and man in Burgundy click here for Part 4.

 

2006 Study of erosion in Vosne-Romanée, Aloxe-Corton, and Monthélie

Two sibling studies, preformed by the same research team, illustrates very well the processes of erosion (detailed in part 4.2), and how it affects the wine we drink. These are multi-discipline studies by conducted by the team of Amélie Quiquerez, Jean-Pierre Garcia, and Christophe Petit from the Université de Bourgogne, and Jérôme Brenot from Géosciences Université de Rennes.

The first of the two studies was published in the Bolletino della Società Geologica Italiania 2006, with contributions by Philippe Davy, Université de Rennes. Entitled “Soil erosion rates in Burgundian vineyards (link).” It examined the erosion rates in the villages of Vosne-Romanée, Aloxe-Corton, and Monthélie. I highly encourage you to look at these important studies to get their analysis, which in some ways is limited by the rigors of science which require the researcher to prove what they already know to be true. My overview of the information revealed by their study applies my own perspective and insights.

The researchers selected three steep, upper-hillside vineyards from which to gather data, all which carried essentially the same average grade, with a mean of 10.5% for Vosne and Aloxe-Corton, with Monthelie the steepest, with a mean slope of 10.7%.  Additional selection criteria were all three were they must meet these three (very traditional Burgundian) vineyard practices.

  1. The rows ran vertically down the hillside.
  2. None of the plots were allowed to have grass grow between the vines.
  3. Frequent plowing or tractor crossings (up to 15 times per year)

However, I note two marked differences between the vineyards. 

  1. How much the slope changed within the plot boundaries.
  2. The length of the slope. 
Vosne Damodes
Vosne Damaudes photo: google earth

The study’s most uniform slope was a vineyard in Vosne, with a fairly consistent 10% to 12% grade. It also had, by far, the longest slope studied, at 130 meters.(1)  This longer slope length, one might expect, would allow water to gain volume, speed, and velocity. These three factors all increase the runoff’s ability to carry larger and heavier particles with higher suspension velocities. Conversely, it was the only slope studied which had a murger (stone wall) at its base, slowing the runoff enough to allow sedimentation to occur, and it would appear to be the only plot with a level spot for sedimentation to rest. 

Although unnamed by the study’s author, I have concluded this vineyard is Les Damaudes on the Nuit-St-Georges border. Clues to its identity include a maximum elevation of 345 meters – the highest in Vosne, and uniform slope of 10-12%. Identifying the parcel location is possible as well, as only one location in Les Damaudes is long enough to fit the 130-meter plot length of this study. When subtracting in the dirt roads at the top and bottom of the vineyard, which are natural erosional breaks, the total length is 126 meters. This vineyard was studied in-depth, over a multi-year period, and spawned the two studies I will detail in this article.

The vineyard in Aloxe-Corton may contain a significantly steeper section than the vineyard in Vosne, with a 17% grade, but overall the Aloxe-Corton vineyard had the same average gradient as the plot in Vosne, at 10.5%. This indicates that part of that vineyard had to contain no more than a 5% grade. Additionally, this vineyard was the shortest plot at 53 meters, meaning as long as fast-moving runoff could not enter the plot freely from above, runoff should not be able to attain the same velocity as it might in Vosne. Because of this, we might anticipate erosion lower erosional levels. There is no specific information that might allow us to identify this vineyard. And while the author Jérôme Brenot included a photo and a brief reference to the grand cru vineyard of en Charlemagne (regarding rill erosion down to the limestone bedrock), the lieu-dits  of en Charlemagne is in neighboring PernandVergelesses, not Aloxe-Corton

Monthelie Clou du Chenes
The section of Monthélie studied is snug against the Volnay border. Here in 2012, some grass is now being allowed to grow between the vines. The vineyard above, La Pièce-Fitte, has one plot that is in pretty poor shape, with gaps between vines, and rills that because of the slight off camber row orientation cut right up against the vines, rather than directly between the rows. photo: googlemaps click to enlarge

The slope in the study with the steepest section, by far, was in Monthélie. The plot there reaches a maximum pitch of 24.5%, but the average gradient is only slightly greater at 10.7%, which again indicates much of the vineyard is gentile in its declivity. This vineyard, which would become a 1er cru shortly after the study was published, is the vineyard of Le Clou des Chênes,(2) and this parcel appears to share a border with Volnay’s ez Blanches vineyard. The study measured nearly twice the plot-wide erosion at 1.7 mm (± 0.5 mm year) as they did in either Vosne or Aloxe-Corton. However, in some locations within Le Clou des Chênes had far greater erosional levels: measuring as deep as 8.2 mm (± 0.5 mm) per year.

Notable is that the time under vine is much shorter, having been planted 32 years before the study. This makes the losses all the more alarming for these steeper slopes because the knowledge of how to resist erosion has improved so dramatically in the past twenty years.  

Data collection and methodology

This much erosion surely has had a tremendous influence on the character of the wines produced from these vines.
This much erosion surely has had a tremendous influence on the character of the wines produced from these vines.

Determining these numbers involved a massive data collection effort, imputing vine measurements on a meter by meter scale. With 10,000 plants planted per hectare, this translates into thousands of data points are required to arrive at the final calculations.

Soil loss was determined by measuring the exposed main framework roots from the current soil level to the point of the graft cut. The graft is typically made 1 cm above the soil level at the time of planting, and with this measurement original soil level at the time of planting can be established (NEBOIT, 1983; GALET, 1993). By dividing this measurement by the number of years since planting, a relatively accurate average rate of erosion can be established. This method of using plants to give a historical record is called dendrogeomorphology, which is a geologic adaptation of dendrochronology, the study of trees and plants to determine the historical climatic record.

An unequal field of study

Photo: Jérôme Brenot et al
Photo: Jérôme Brenot et al

In the end, there was a single factor that differentiated these study vineyards: the road and the stone wall below the Les Damaudes vineyard in Vosne. Because of this road and wall, it also was the only vineyard that had an area at the base of the slope that was able to retain alluvial sediment. This proved to be an important last gasp defense regarding soil loss and allowed that sediment to be returned to the slope. With this material, workers could fill the rills in Vosne, that would grow into gullies down to the base rock in Aloxe-Corton and Monthélie.

The return of the sediment to fill the rills was preformed bi-annually in the Les Damaudes parcel. However, the owners of this vineyard were lucky rather than preventative. The wall was built as the headwall of the small clos that surrounds the vineyard below, and the access road that runs between the vineyards proved to provide the necessary flat collection area for the alluvium.

Inexplicably, the author chose to simply say that in Monthélie, the practice of returning  soil to the hillside had never been done, whereas in Vosne it had been practiced every two years. Strictly speaking this was true.  However when looking at satellite images of the vineyard, this statement appears somewhat disingenuous. In reality, the decision to plant the entire area Le Clou des Chênes in long rows without any roadways or other vineyard breaks, when coupled with the  parcel’s physical position on the hill, created a highly erodible vineyard in which no level “toe of the slope upon which might sediment gather. Returning sediment, that doesn’t exist, to the hillside is simply not possible. That does not excuse the vineyard owner from not removing vines to build a walls or taking other erosion prevention measures, but it also gives and indirectly assigns blame for this lack vineyard maintenance. The Aloxe-Corton parcel (where ever it was) is not mentioned as the owners never having returned alluvial sediment to the hillside, although this was apparently the case.

In 2006, the researchers took the adjacent photograph of Le Clou des Chênes, showing that rills had developed into gullies due to the lack of effective intervention by the grower. They also included photo looking up towards the Bois de Corton (which I have not included), with a rill/gully that extends down to the raw limestone base rock below.  In each photo, the vines roots can be clearly seen, having been exposed by the continuing erosion of these gullies. 

Study design: did the study reveal unexpected results?

In some ways, the wall below the parcel in Vosne was problematic to the study. The stone wall, and ability the return of the sediment by the grower directly impacted the amount of erosion recorded. The study’s author reports this in the write-up as: “by a factor of two”.  It not clear that the researchers anticipated this would be such a weighty factor when they formulated the study, since the focus of the study did not seem to take into account the effectiveness of wall in diminishing erosional forces. However the effect of the wall and the “anthropogenic factors” (meaning in these studies: the actions by man of returning the sediment to the hillside) certainly did have a dramatic effect on reducing the total soil lost, and the authors rightly took the opportunity to underscore the roll and value of murgers and clos as a primitive, but effective form of erosion control. (4)

But because of the wall (and the author’s eventual focus on it), other opportunities were lost. Since Les Damaudes in Vosne possessed the longest slope which also had the most consistent gradient, knowing how those factors affected erosion would have been instructional.  Had the erosion measurements been made before the anthropogenic resupply of the sediment to the slope, this information might have been gained. But since the measurements were taken after the rills were filled, ascertaining the impact of degree of slope and the length of the run can not be readily determined if the Vosne parcel is included in the analysis.

Further analysis of  meter by meter grid data, might answer some of these questions surrounding how much erosion is affected by increasing slope gradient and increasing slope length. Here the shorter Aloxe vineyard could have been compared to the top 53 meters of the steeper Monthélie vineyard. What were the erosional differences within these sections? What was the difference between erosion between the upper slopes and the lower slopes of the vineyards. Could these differences have been attributed to gradient or soil type? What were the soils left behind in the inter rows? Were they significantly different to the soils directly under the vines where the soil is more protected from rain strike and rill erosion? Then, if the full length of the Aloxe vineyard could be included, would there be greater erosion on the steeper sections where gravity has more effect? What about on the lower sections of the plot where increase water volume, speed and velocity might be expected to increase? It does not appear that these questions were asked by the study’s researchers in 2006.

It would be interesting if the data still exists and can be analyzed to examine those questions as well. It certainly would shed a more quantitative light on erosional forces on Burgundian hillside vineyards.

Study’s Opinion

In the opinion of the study, while in the short-term, erosion didn’t affect the vines production as long as the root system was not exposed, over time, the overall surface soil level declined despite the best efforts in Vosne to return the alluvial sediment to the hillside. At the time of the study, the most alarmed of growers had begun been attempting to restrict erosion by allowing grasses to grow between rows, shortening the length of rows and rebuilding walls. The authors suggest these processes be applied to all hillside vineyards.

The study of a single rain event in Vosne-Romanée

The second study released by this team in 2007 is far more detailed, focusing solely on the Damaudes vineyard. Entitled,Soil degradation caused by a high-intensity rainfall event (3) the paper details soil loss related to a single storm on June 11, 2004. This study is much more focused and is far more precise and instructional in its findings.

Vosne Damaudes erosion study
Click to enlarge.

The study’s centers on the erosional path, volume, and sediment type, as well as the net erosion levels measured in the vineyard after workers had returned sediment to the hillside, post-storm.

Soil analysis of the plot

The soils native to the vineyard are within this description from the text of the study. The prose is tight and dense so I will quote the author, Emmanuel Chevigny, here.

“The texture is rather homogeneous over the whole plot and is composed of 40% of clays and silts, 50% of gravels (2 mm to 10 mm) and a low sand and boulder content. The topsoils are ploughed (Mériaux et al., 1981). The argillaceous aggregates with polyhedral blunted to grained form are slightly structured. No pedogenetic segregation has been observed.”

The soil, as described, is a marl, with what I would think has a surprisingly high clay content for being this high on the slope. A better breakdown of clay and silt would be informative, because (as detailed in Part 2.1  and 2.2 regarding soil formation), clay is metamorphosed from limestone and other materials, and very fine in size, while silt is larger (between 0.0039 to 0.0625 mm), and not metamorphosed. Silts are often parented from quartz, which unlike limestone is not prone to chemical alteration, and thus will not produce clay minerals. The origin of this silt must have been transported from farther up-slope, having arrived in Les Damaudes through erosion.

The vineyard’s soil has a low sand content.

The author then writes about argillaceous aggregates, which are clay aggregates. In this sentence, they are writing about the type of soil structure found in the vineyard. Clays tend to form into blocky structures, where each clay units sides is the same shape or a cast of the aggregate next to it. In other words, when the blocky structures form, they are literally cast so that they fit together like a puzzle. Here he is saying that the edges of these casts of the aggregates have been blunted making them more grain like.  There is a soil type, classified as granular (grain-like), that is common to soils in grasslands with a high organic content, and Chevigny is clearly saying these are not granular soils.

Lastly, Chevigny notes that the researchers observed no pedogenetic segregation, meaning they could observe no identifiable soil creation nor the beginnings of soil horizons (sedimentary layering). This would lack of soil generation could be caused, in part, by plowing which disrupts soil horizons and encourages the erosion of weak young soils that have not developed into stronger aggregates. More on the concept of what soil is and pedogenesis later.

The gravel, or scree, which constitutes 45 percent of the vineyard’s soil makeup, (by definition) has slid into the vineyard by gravitational erosion, from higher on the hill. With the clearing of land and subsequent planting of the vines, this gravel has long ago been plowed into the clay-silt mixture. It is never mentioned by the study author, whether the scree is primarily limestone or not. Limestone is not a factor for these researchers, the particle size is squarely considered to be the issue.

By the numbers

While study revolves around the analysis of a tremendous amount of numerical data, to examine each piece of analysis is beyond the scope of this article, but their findings are none-the-less important and tells the story of erosion within a Burgundian vineyard very well. Below I’ve listed what I see as the most important changes to the hillside following this particularly heavy storm system:

  • Both rill and sheet erosion occurred, but rill erosion accounted for approximately 70% of all soil lost from the hillside.
  • A total of 13 rill erosion were noted, some forming a mere 30 meters from the upper plot boundary, that ran in straight lines down the slope, each time in the inter-rows.
  • Rills occurred across 59% of the inter-row area
  • The rills were U-shaped with strong vertical walls.
  • Estimated soil loss from the rills alone was 4.77 meters
  • A rill erosion for this rain event is estimated at 7.8 cubic meters (.275.5 cubic feet) and weighing roughly 6 metric tons (13,227 lbs)
  • An estimated 1.6 meters erosional material was deposited into 7 alluvial fans at the base of the plot.
  • The sedimentary fans consisted primarily of very fine sand to coarse sand that was between 63 μm (roughly the thickness of paper) to >2 mm. Only 10% of the fan sediment was silt clay fractions of less than 63 μm
  • Fan #4 had a total sediment area one-half of a meter cubed (.5m3).
  • The two rills that fed fan #4 had a total eroded area of .93m3  *
  • If 10% of the rill volume is sand, then 70 percent of the fan debris came from the rills while a remaining 30% must have come from surface erosion which fed into the rills and were deposited into the fans.
  • Topographic soil loss in inter-rows with rills was 3.9 mm, or 48 metric tons per hectare (105,800 lbs)  even after anthropogenic resupply of fan sediment to the hillside.
  • Mean (average) soil in non-rill effected vineyard area, was 1.4 mm, or 24 metric tons per hectare (52,900 lbs)

*1 cubic meter is equal to 1000 liters, or 6.29 oil barrels or 264 U.S. fluid gallons.

Storm size and frequency

Annual rainfall in the  Côte de Nuits is between 700 and 900 mm (27 inches to 34.4 inches) per year writes Chevigny, citing the Météo France weather service’s Atlas climatique de la Côte dOr 1994.*  The study also cites that storms with rainfall of more than 30 mm per day, occurred 10 times between 1991 and 2002. Nine of these rain event dropped between 30 and 50 mm, (1.1 inches to 2 inches) and a single storm dropped 63 mm (2.5 inches) of rain water per event/day. Based on this, we might expect that there have been 50 such events between planting and the 2006 study.

The storm event of June 11, 2004, was uniquely powerful because 40 mm fell in a two-hour period, which caused causing 3 times the annual erosion rate established by the 2006 study of 1 mm per year. Perhaps most importantly, the erosion of this single event is averaged into that 54 year period. This indicates that some years little erosion occurred. Because the study only includes storm records from 1991-2002, we can’t estimate the distribution of erosion over the span of these 54 years.

With global warming, storm intensity seems to be on the upswing in Burgundy, just as scientists have noted in other parts of the world. The severe hail events of 2012, 2013 and 2014, which centered over the hapless villages Pommard and Volnay, resulted in total crop loss for some growers.  In the Côte de Beaune, where precipitation and hail has recently been at its most extreme, has also been remarkably varied in its distribution. According to Jancis Robinson, in July of 2013, Volnay saw 57mm of rain (2.25 inches), while neighboring Monthelie only got 9.4mm. Needless to say, with this high degree of weather localization, these data figures are representative of the rainfall collection points only. There were likely areas of Monthelie that got much more rain, and areas Volnay that got much less rain than the data collection sites.  The massive storms of late November 2014 that saw 200-300 mm of rainfall along the Mediterranean coastline and into Austria, the Dijon saw 95 mm of rainfall over a 24 hour period. So, in terms of storms, it would appear that while the Côte d’Or gets regular, low volume rain events, it is by and large, relatively protected from major storm fronts.

*Current monthly statistics are can be found here, and the average rainfall in Dijon as of 2015 is 775 mm (30 inches) per year.

The sediment at the “toe of the slope” 

When examining sediment in the alluvial fans, researchers discovered that it was made up of 90% sand and 10% fine sediment. Fan number four, on which researchers focused their examination, contained nearly one meter of alluvial material. The fact that it contained little silt or clay, indicates that when the water became backed up at the stone wall, its movement did not slow enough for particles smaller than 63 μm (which includes all clays and silts) to fall out of suspension. This suggests there was a significant depth of water Then as the runoff began to gather enough volume to circumvent the murger, and continue downslope, it gained sufficient speed and velocity to quickly form rills in its path around the wall. The runoff carried virtually all particles smaller than fine sand out of the vineyard.

Study inconsistencies, and outdated or generic source material

Between the two articles, the explanation of soil and bedrock type differs. It is not clear why the authors of both studies would quote articles that are 35 to 45 years old, and that generic to the region rather than performing a shallow excavation themselves, in order to obtain information specific to that vineyard.

“The slopes are composed of Middle to Upper Jurassic limestones and marls (Mériaux et al, 1981) …“For example, the sandy-clayey screes (grèze litée) reach 3 meters on Comblanchien limestones in Vosne-Romanée.

In the second study they write:

“The hillslopes develop on Middle to Upper Jurassic limestones and marls, and are covered by colluvium soils of argillaceous-gravelly nature and formed by Weichselian cryoclastic deposits (grèze litées) reaching up to 3 m thick (Journaux, 1976).”

Writing of Comblanchien as a class of limestones is a red flag, as it is distinctly a singular type of limestone. Adding to the confusion is the soil percentages that at first appear to be attributed to the vineyard, are actually from the 1981 Mériaux et al study and generic to the  Côte d’Or. Later in the study, the percentage of sand is increased to >20% (from 10% sand and larger stones). 50% gravel content in the vineyard, which is cited in early in the text, is reduced to 45% later in the study write-up.

 

Computer modeling projects grain-size transition 

Computer projections of grain size changes after each major storm event.
Computer projections of grain size change after each major storm event. Click to enlarge

Because the researchers must begin their work with the soil percentages they observe, this 45% gravel, 40% clay/silt and 15% sand, was their starting point. It was quickly recognized that outgo of clay minerals, coupled with the simultaneous retention of sand would eventually change the vineyard make-up, so they developed a computer program to predict future changes in grain size distribution of the soil composition. Computer models showed after only 4-5 rain events of similar magnitude as the one in 2004, there would be significant changes to the soil makeup. The results of those projections are to the right.

Chevigny encapsulates their findings with this statement.

“…the results of our simulation clearly show that repeated rainfall events modify significantly and very rapidly surface soil grain-size distribution: after only a few events, the top soil has lost more than 30% of its fine material.”

The ultimate effect of this would be the loss of organic materials, nutrients and ultimately soil sustainability.

Study conclusion: vineyard practices enhance rill development and erosion

While the wall slows the net output of soil volume from exiting the plot, the most soils most viable for farming are being lost, while simultaneously, the soil texture and particle size are being irrevocably changed as the sand sediment is returned to the hillside, and disked back into the soil.

It is forwarded by the author, that this action, is part of the problem since rills continue to re-emerge in the same locations, year after year. They submit that ill propagation in the inter-rows is heightened by tilling and repeated passes tractors and foot traffic, and the regularity of rill spacing are evidence of this.  These practices, he writes causes decreased soil porosity (compaction) and restricts rainwater infiltration. Such wheeled ‘passage’ creates flow zones which increase the volume and velocity of runoff in a concentrated area, multiplying the quantity and size of material the runoff can carry. The evidence of these anthropologically created flow zones is the re-emergence of rills that return, repeatedly, in the same inter-rows, despite workers attempts to eliminate them by filling the rills and disking those areas.

It is clear the effort must be made to properly identify the flow zones and attempt to eliminate them but to do so is to understand their formation to begin with, and limit or eliminate that activity altogether.

For me, the results of the computer modeling and projections are not surprising. While this research team and Burgundian winemakers can only look forward to what is next, we have the opportunity to use this information to hypothesize what came before.  This will allow us to see the true arc of geomorphological progression in the vineyards, and thus how winemaking styles have and will continue to change in Burgundy.

Next UP:  Turning our understanding of the limestone Côte on its head

 

 


 

(1)  Vineyards typically are areas with no breaks or obstacles to slow or impede storm runoff, so longer vineyards tend to suffer more greatly from erosion. However, this was not identified as an erosional factor in the study write-up. The length of this Vosne vineyard was listed in the first study at 130 meters, while in the second study it was written as 126 meters.

(2)  Le Clou des Chênes’ increased prestige and vineyard value can be a tremendous incentive to better maintain a vineyard. The vines and vineyard appeared to be in good health in 2012, the last time googlemaps car drove up this stretch of road. Still, no murgers had been built as of that time.

(3) published by Emmanuel Chevigny of the Université de Bourgogne in 2007

Understanding the Terroir of Burgundy: Part 4.2 Erosion: fundamentally changing terroir

Erosion banner

 

 

Erosion is constantly changing the terroir of Burgundy, and in turn, it is altering the weight and character of the wines from virtually every vineyard on the Côte. How significant is erosion in Burgundy today? As mentioned in Part 4.1, a study during the late 1990’s measured the soil loss in unspecified vineyards of Vosne-Romanée to be 1 mm per year, and the same erosional levels were measured off of the vineyards of Aloxe-Corton.  Ath that alarming rate, losses over the next century would have averaged 10 centimeters or almost 4 inches of topsoil if corrections were not taken. On the even steeper slopes of Monthelie, a study measured almost twice the erosion at 1.7 mm (± 0.5 mm year), with sections of the vineyard which measured a shocking eroded up to 8.2 mm (± 0.5 mm) erosional rate. Luckily, many growers have improved their farming practices, particularly since 2010, and these figures should be lower today. Only future studies can tell us what improvement has been made.

The grape harvest Annonymous 16th century, Southern Holland
“The grape harvest” Anonymous 16th century, Southern Holland

For centuries the solution for this problem was to bring in soil from outside areas to replace what was lost on the slopes of the Côte d’Or. However, in the name of terroir, this is no longer allowed. Current law allows growers to redistribute only the alluvium that comes to rest within appellation boundaries. One can imagine that the laborious process of shoveling out the alluvium from the toe of the plot and redistributing higher in the vineyard is a yearly chore. What earth escapes the appellation lines however, is gone to that appellation forever.

The intention of preserving the purity Burgundy’s unique terroir by forbidding introduction of exogenous soils is somewhat paradoxical, since it is only attempting to preserve the terroir à la minute. While in reality it is ultimately is failing at that – due to erosion. 

A positive, unintended consequence of this inability to replace soil is that growers have finally realized that soil conservation is now more critical than any time in Burgundies’ 1500+ year-old viticultural history. They now know that they must fully understand the factors of soil structure and erosion, while at a municipal level, their villages must invest in effective storm water management; both of which are in various states of development or improvement. 

The long uninterrupted run of vertically oriented rows presents unrelenting erosional pressures on this section of Les Folatieres.
The long uninterrupted run of vertically oriented rows presents unrelenting erosional pressures on this section of Les Folatières. photo googlemaps

While the best modern practices are stemming the tide of erosion, vineyards still can be threatened. Even great vineyards on the mid-slope, like Les Folatières in Puligny-Montrachet, which have long, open stretches of vines without significant breaks in planting, are prone to extensive erosion. While soils are depleted not only in terms of depth, they are changing in terms of particle size and makeup. Erosion most easily targets fine earth fractions, detaching them from their aggregate groupings, and sending them into vineyards farther down slope. Light to medium runoff acts like a sieve, carrying away only the smallest particles, leaving behind material with of larger particles sizes. This in a very real way changes the vineyard’s terroir, and in turn, the wines that are grown there. Wines from vineyards that retain only course soils of large particle size (1) tend to produce wines with less fruit the and less weight, and by consequence revealing a more structured, minerally character.

Even more critical is that soil loss can threaten the vitality and health of the vines, as the soil is literally carried away from beneath them. A vine’s main framework roots is said to require a minimum 11-13 inches to anchor itself to the earth and survive. The problem arises when a section of vineyard does not have extensive fracturing, and the soil level begins to drop below that one foot level. To address this, various growers have responded by “reconditioning” their land. By using a back hoe to break up the limestone below, this can give new vines planted there the living space so the vineyard can continue. Does this change the terroir and the future wine more than inputs of exogenous soil? I should think the answer is yes, significantly. 

 

Rainfall and rain strike: the first stage of erosion

rainstrike. photo: agronomy.lsu.edu/
rainstrike. photo: agronomy.lsu.edu/

Rainfall is measured by its size and velocity. A raindrop from a drizzle is typically .5 mm in size, and has a terminal velocity (the maximum speed the drop can reach) of 2 meters per second, or 4.5 miles per hour, in still air. The speed it falls, with no assistance from the wind is determined by its ratio of mass to drag. Large raindrops of 5 mm, have more mass in relationship to its drag and accelerate to 9 meters per second, or 20 mph.

Rainfall, meaning the actual physical strike of each drop, can break down soil aggregates (fine sand,  silt clay, and organic materials) and disperse them. Splash erosion has been recorded to drive particles of earth up to 60 cm into the air, and 1.5 m from its point of origin.

Once their limited bonds are broken, the ensuing runoff can carry these materials downslope. Runoff, the most obvious form of erosion, occurs when rainwater cannot infiltrate the soil quickly enough, and exacerbated by the lack of cover crop, lack of organic material, lack of soil structure and negative effects of soil compaction. Of course, this process is most noticeable during high-intensity rainstorms, the amount of soil lost during longer but low-intensity rainfall can be significant. This slower erosion can go largely unnoticed until most of the productive topsoil has been removed by what is referred to as sheet erosion.

Seasonal protection from rainstrike

Compared to most growing regions, the Côte d’Or has a very wet growing season. Storms during this period can bring irregular and unpredictable rain events that can be heavy and long in duration. The winds during harvest tend to be westerly, with warm humid winds bringing rain first over the Hautes Côtes, then to the Côte d’Or, then out across the Saône Valley. The wet warm humid conditions often encourage powdery mildew in the wake of the storms, so there is a tendency to want to prune to open up the canopy for ventilation to prevent mildew. However, the vine canopy can provide significant protection against rainfall strike, depending of course, on the orientation the rows and the of the wind direction. So good canopy coverage for the period that half of the precipitation occurs (April – September)(2) is beneficial in terms of protection from erosion.

As winter arrives, the vines will have lost their foliage, exposing the soil directly for the entire winter and spring to whatever nature has in store.

Rain Rate

storm.1
Summer storms. Bottom right Photograph: Louise Flanagan theGuardian.com, Bottom left photo Caroline Parent-Gros of A.F. Gros, Top photo Decanter.com

Rainfall is typically measured in millimeters per hour, with a light rainfall slightly tipping the scales at up to 2.5 mm per hour or less than a tenth of an inch per hour. Moderate rainfall is considered to be from 2.5 mm per hour to 10 mm per hour. A heavy rainfall falls between the range of 10 to 50 mm, and a violent rainfall is above 50 mm per hour.

 

Light rain – drizzle 2.5 mm per hour with a terminal velocity of 2 meters per second

Moderate rain 2.5 mm per hour to 10 mm per hour

Heavy Rain  10 mm per hour to 50 mm per hour

Violent rain, above 50 mm per hour

 

Good soil structure resists damage from rainstrike and runoff

Good soil structure is the result of the binding of soil into clumps of both small and larger aggregates, meaning sections of soil will bind more strongly together, than those next to them. This allows the soil to maintain the necessary small and large pore spacing, which allows water, air and nutrient infiltration and movement through the soil. Larger amounts of older, more stable organic matter tend to strengthen soil aggregates so any farming practice that increases organic matter, and the subsequent microbiological activity will result in healthier soils.  Stable soil aggregates allow the soil to resist disintegration due rain strike and thusly helps deter erosion.  It also encourages root penetration by creating weak spots between aggregate masses.

Conversely, unstable soil aggregates are more easily dispersed by rainstrike, and the ensuing erosion clogs larger pore spaces of the surface soil. This clogging forming hard crusts on the surface which both restricts both air and water absorption and increases runoff.

The fix apparently is simple. According to soilquality.org, soil forms aggregates readily with the addition of organic manure, as well as allowing cover crops to grow, which has the additional benefit of protecting the soil from rain strike and the ensuing erosion.

Infiltration rate

Erosion Runoff Ardeche
Rill Runoff running fast in Ardeche. Photo http://www.geo.uu.nl/

The speed at which rain can be absorbed into the soil is referred to as infiltration rate. An infiltration rate of 50 mm per hour is considered ideal for farming, because even in heavy rainfall, a well-structured loam will not allow puddling. While the farmers of Burgundy do have some loam in their soils, the geological and topographical factors they face are far more and varied and thus more complex than that of the typical farming situation. I could find no studies done specific to infiltration rates of Burgundian soils, but below are the general rain infiltration rates of general soil types, starting with clay.

The infiltration rate of clay soils, with good to average soil structure, unsurprisingly, do not drain all particularly well, due to their very small-sized particles. Clays typically have an IR of 10mm-20mm per hour. And as we know, transported clay, with its aligned particles, and plasticy quality greatly restricts water flow, and while it will absorb water, it will not allow water to pass through until the entire structure is saturated, greatly slowing drainage. Worse, due to poor farming practices, clay soils can have a decayed structure, which can slow absorption to less than 10 mm per hour. Water tends to puddle on clays with poor structure, causing them deteriorate to the point of deflocculation.

The study of water and how it drains is researched acutely in areas where water is scare, whereas little study of drainage is done in France where rain and water are plentiful. Hence, my investigation of water infiltration in calcium-rich soils lead me to agricultural water policy studies conducted in Palestine and Spain. One such study found that Clayey Marl, with a plasticy character, had an infiltration rate of only 4-8 mm per hour. This low rate of infiltration suggests the soil structure had already been degraded through poor farming practices. Often the villain of low infiltration rates is a combination of frequent deep tillage, herbicide and pesticide use and compaction by walking on or working wet soils, which collapses weaken soil aggregates.  In deeper soils, like at the base of the slope, collapsed soil aggregates can result in hardpan development below ground, while on sloped vineyards, disrupted soil aggregates are very susceptible to erosion.

Clay-loam and clayey-marls, like those found on many lower-slope vineyards, that retain good soil structure, have IR rates beginning at 20 mm per hour. As the percentage of loam increases (equal parts sand, silt, and clay) the IR rate increases up to 50 mm per hour as long as it retains good aggregate stability and there is no compaction.

Loam to sandy soils, which some Bourgogne-level and Village-level vineyards possess, can have very good infiltration rates, again as long as soil structures are good.  Ideally, they can absorb 50 mm of rain per hour, which is the amount that a heavy rainstorm will produce. These vineyards, however, receive all the runoff from the slopes above, and their “well-drained” soils can be overwhelmed.

Sandy soils and Calcareous (limestone) soils can have infiltration rates well in excess 150mm per hour to 200+mm per hour. The problem is these soils drain excessively well, and tend to not retain water well, and are prone to high evaporation rates.  Off point, but quite interesting, are two studies in south-eastern Australia Bennetts et al. (2006) and Edwards & Webb (2006) found that rainwater remained relatively unchanged as it moved though these porous soils that lacked significant amounts of fine earth fractions and organic material. However, water changed its chemical signature quite significantly as it passed much more slowly through clay-rich soils. This finding certainly challenges the long-held assumption that it is the limestone lends many Burgundies their mineral character.

Infiltration Rate, Slope, and Runoff.

Vogue's parcel of Musigny. Source Googlemaps
Vogue’s parcel of Musigny. Grass growth does not seem to be encouraged here. Given Cerdà’s study regarding the erosion of bare soils, one can only wonder how much greater this vineyard could be? The mitigating factor is the vineyard runs horizontally along the top of the hill, and is not deep or highly sloped. Runoff has little opportunity to gain significant suspension velocity. Photo Source googlemaps.com

A study in Spain by A. Cerdà (Univ. de València) examined infiltration rates, runoff, and erosion, on clay, marl, limestone and sandstone. Additionally, he ran these trials with three levels of vegetation covering the soil material: bare, intermediate and vegetated.  The amount of water delivered was 55 mm per hour (which some soils easily absorbed). The study showed slower rates of infiltration on the bare soils, while more highly vegetated soils reduced and almost eliminated runoff and erosion.  Interestingly, marl soils fare the worst for both runoff and erosion rates on bare soils. Yet on vegetated soils, runoff and erosion of the marl were minimal.

They observed, of bare soils, an infiltration rate of  3 to 55 mm per hour, the runoff from 0 to 83%, and the erosion rates from 0 to 3720 grams per hour.

The easily erodible marl soils had up to 83% runoff and a maximum erosion of 3720 grams per hour. So it turns out that marl soils are particularly vulnerable to erosion which sets up an interesting dichotomy: Burgundian’s penchant for discouraging ground cover between the vines, actually encourages erosion – something they seek to, and direly need to avoid.

Clay (soil) and limestone (soil) both had what Cerdà considered to be intermediate levels of runoff and erosion; with a maximum of 46% runoff, and a maximum of 131 grams of soil material eroded per hour.

When we talk about erosion, we are implying there is a slope.

Nearly level: Level, 0% Nearly level <3%
Gently sloping: Very gently sloping >1%, Gently sloping <8%
Strongly sloping: Sloping >4%, Moderately sloping <8%, Strongly Sloping <16%

Source: nrcs.usda.gov

On the rockier terrain of upper slopes, the uneven the soil surface can slow the momentum of water coming down the hillside, despite the steeper grade. However, as the runoff moves downslope, and the soil becomes smoother, the water grows in volume as in joins other rainfall which has not yet infiltrated the topsoil. This increase in volume causes the runoff to increase in its speed and its velocity. Speed and velocity increases are exponential, as its mass allows it overcomes the friction of moving over the soil below. 

Despite the fact that these moderate slopes can attain fairly significant soil depth with normal, moderate rainfall, they are also prone to erosion when exposed to heavier storm-induced runoff. Any long, uninterrupted stretch across these moderate slopes encourages a fast, and often damaging, runoff. As the speed of the water increases, it achieves a volume sufficient to carry larger and larger particles. Cerdà’s study suggests that the marl that has developed on these slopes are particularly vulnerable to heavy runoff if no vegetative cover is allowed to grow among the rows. 

Suspension velocity

water suspension velocity
water suspension velocity source: water.me.vccs.edu/

The ratio of surface area to weight determines a soil particle or rock’s suspension velocity. This is the amount of water velocity needed to carry the object in its flow. As the flow decreases, rocks with higher suspension velocity, meaning they require fast-moving water to carry them, settle out quickly, and are said to have a low settling velocity. As the water slows, it is these, the densest objects, that fall out of suspension first.

Silt and Clay particles have a very low suspension velocity due to their extremely small size, regardless of their density. These particles are easily picked up and washed away by water movement. Unless the clay particles in suspension are adsorbed as it slowly passes a homogeneous clay body (ie. a kaolinite clay body attracts kaolinite clay particles and illite particles will flocculate with an illite body), clay particles will not settle out of solution until the water becomes still and ponds. The same is true with silt, with its slightly larger particle size.

Sand and gravel are larger, with enough density to resist slow-moving water. They are considered to have a higher suspension velocity than silt or clay. But neither sand, gravel, nor even rocks the size of the palm of your hand, are immune from alluvial transport.

Up next: Erosion 4.3 In the water’s path: Studies of Erosion in Vosne

 


(1) It could be argued that because of Burgundy’s monoculture and high erosion rates will only allow calcisol, and because of that soil development (pedogenesis) is not possible due to the filtering out of fine particles, both mineral, and organic, by erosional processes. Conservation tilling or zero till could greatly change that dynamic, and it is possible with these and other techniques, that growers could expose the truer terroir of Burgundy.

(2) The Wines of Champagne, Burgundy, Eastern and Southern France,  by John J. Baxevanis Rowman & Littlefield Publishers (October 28, 1987)

(3) Could this chemical signature change the flavor of wine? This certainly raises a whole host of questions regarding the impact of fast draining limestone on the flavor or minerality of in wine. This study would suggest the long-held belief by many that limestone gives wines a minerally characteristic is false.

 

 

Understanding the Terroir of Burgundy: Part 3.3 The Upper Slopes

Shallow topsoil over hard limestone: a site of struggle

As I touched on in the introduction of slope position in Part 3.2, there are significant variables effecting which vineyards can produce weightier wines further up the slope. However, as a general rule, the steep upper-slopes are far less capable of producing dense, weighty and fruit filled Burgundies that are routinely produced on the mid and lower slopes.

The lack of water, nutrients and root space

The scree filled Les Narvaux in Meursault. photo: googlemaps
The scree filled Les Narvaux in Meursault. photo: googlemaps

In many of these upper vineyards, the crushed, sandy, and in some places powdery, or typically firmer and more compact, the marly limestone topsoil overlies a very pure limestone, such as Comblanchien, Premeaux and Pierre de Chassagne. Here, the extent of that the stone is fractured determines the vines ability to put down a healthy volume of roots to support both growth and fruit bearing activity. Any gardener can tell you that insufficient root space, whether grown above a shallow hardpan or in a pot, will cause a plant to be root bound and less healthy.

Because these steeper vineyards can neither develop, nor hold much topsoil to its slopes. The topsoil, which can be measured in inches rather than feet, tends to be very homogeneous in its makeup; a single horizon of compact, marly limestone, with a scant clay content of roughly 10-15%. The infiltration of rainwater and the drainage are one and the same. Retention of the water is performed almost solely by this clay content, and evaporation in this confined root zone can be a significant hazard to the vine. Fortunately rain in Burgundy during the growing season is common, although rainfall from April to October, and particularly in July, the loss of water in the soil is swifter than it’s replacement from the sky (Wilson, “Terroir” p120).

Infiltration Rates of Calcareous Soils

A study by A. Ruellan, of the Ecole National Supérieure Agronomique, examined the calcareous (limestone) soils of Mediterranean and desert regions, where available water and farming can be at critical odds.  He studied two major limestone soil types. The first was a light to medium textured, loamy, calcareous soil (60 – 80% CaCO3), and the second was a powdery and dry limestone soil with no cohesion. This second soil had a calcium carbonate content that exceeded 70%, and had 5% organic matter and a low clay content. The water holding capacity of this soil was a mere 14%. The depth of this soil was over 2 meters deep, which likely does not allow weathered clay accumulate near the surface, as it does in Burgundy.

Both limestone soils had very high permeability, with an infiltrate at a rate at a lightning fast 10 to 20 meters per day (or between 416 mm per hour and 832 mm per hour).  Even if rainwater infiltrated at half that rate through Burgundy’s compact limestone soils, it would virtually disappear from the topsoil. This is the area where the majority of the vines root system exists, and part of the root system responsible for nutrient uptake is within this topsoil region.  In this case of these soils, the vines must send down roots to gain water in the aquifer. Wittendal, who I wrote of in Part 3, suggests in that the vines literally wrap their roots around the stone, and suck the water from them.  I have seen little evidence that limestone actually absorbs water due to many limestone’s high calcium content and lack of porosity. This would be particularly true on the upper slopes under consideration now. It would be up to the roots to attempt to penetrate the stone in search of the needed water.

The root zone

Root development through soil
This slide represents the root development in shallow topsoil over a lightly fractured limestone base vs a deeper soil situation with four or five separate bedding horizons, such as exists lower on the slopes of burgundy.The effect infiltration rates have depends significantly on the distribution of vine roots. In most planting situations, 60 percent of vine roots are within the first two feet of topsoil, and have been known to attain a horizontal spread of 30 feet, although the majority of the root mass remains near the trunk.

By design, vines rely on the roots established within the surface soil – which is where nutrients (ie nitrogen, phosphorus, potassium) are found – to gain the majority of their sustenance. They send down deeper roots to gain water when it is not available nearer the surface. However in Burgundy, many of the steeper slopes present planting situations where not only is the soil very shallow, but the nutrients are poor. The limestone in these vineyards often is hard and clear of impurities, and within the same vineyard may vary significantly in how fractured the stone is. Because of this, in some locations vines have difficulty establishing vigorous root penetration of the limestone base, and this can dramatically limit the vine’s root zone.

Additionally, because of the soil’s shallow depth, , and because of the soils high porosity and low levels of clay and other fine earth fractions, only a limited volume of water can be retained

Water is critical for both clay’s formation and its chemical structure, and the clay will not give up the last of what it needs for it own composition. The evaporation rate of what little water there might remain, can be critically swift.

Rainwater’s infiltration of the limestone base, and its retention of water can also be limited where significant fracturing has not occurred. Any water that cannot easily infiltrate either the soil or the limestone base, will start downward movement across the topsoil as runoff. That means any vine that has been established in shallow topsoil, or the topsoil has suffered significant losses due to erosion, will be forced to send roots down to attempt to supply water and nutrients.

Vine roots and a restricted root zone

In non-cultivated, non-clonal vines, powerful tap roots are sent down for the purpose of retrieving water when it is not available in from the surface soils. However our clonal varieties are more “highly divided” according to the “Biology of the Grapevine” by Michael G. Mullins, Alain Bouquet, Larry E. Williams, Cambridge University Press, 1992. The largest, thickest, roots develop fully in their number of separate roots, by the vine’s third year, and are called the main framework roots. Old established vines in good health may have main framework roots as thick as 100cm (40 inches) thick. This main framework root system, in normal soils, typically sinks between 30 cm (11 inches) and 35 cm (13 inches) below the surface.  In shallow soils, they may hit hard limestone before full growth, and may have to turn away, or stop growing. Anne-Marie Morey, of Domaine Pierre Morey, echoes this in talking with Master of Wine, Benjamin Lewin, of their plot in Meursault Tessons. “This is a mineral terroir: the rock is about 30 cms down and the roots tend to run along the surface.”

From the main framework, grows the permanent root system. These roots are much smaller, between 2 and 6 cm, and may either grow horizontally (called spreaders) or they may grow downward (known as sinkers).  From these permanent roots grow the fibrous or absorbing roots. These absorbing roots are continually growing and dividing, and unlike the permanent roots, are short-lived. When older sections absorbing roots die, new lateral absorbing roots to replace them.

This cutaway of the topsoil of Gevrey Bel Air shows just how limited the root zone is in this premier cru vineyard. The Comblanchien below is being 'reconditioned' in this plot. More on this in a near future article. click to enlarge.
This cutaway of the topsoil of Gevrey Bel Air shows just how limited the root zone is in this premier cru vineyard. The limestone below is being ‘reconditioned’ in this plot. click to enlarge.

Although the permanent sinker roots may dive down significant depths, the absorbing roots (which account for major portion of a vine’s root system account for the highest percentage of root mass, typically only inhabit the first 20cm to 50cm, or between 8 inch and 19 inches of a soils depth (Champagnol,  Elements de Physiologie de la Vigne et de Viticulture Générale 1984). Clearly this is an issue if the topsoil is only 30 cm (12 inches) to begin with.  If the absorbing roots are not growing sufficiently on the sinkers, the vine must rely on the exceptionally poor topsoil of the marly limestone.

South African soil scientist Dr. Philip Myburgh found (1996) that restricted root growth correlated with diminished yields. He also found that the “critical limit’ of penetration by vine root was 2 MPa through a “growing medium”. Weakness in the bedrock, and the spacing of these weaknesses, contributed to a vines viability.

The vines on these slopes, on which there is limited fracturing of the harder, non-friable limestone, have difficulty surviving. These locations often shorten the lifespan of the vines planted there, compared to other, more fertile locations in Burgundy, where vines can grow in excess of 100 years. It is these vines, with barely sufficient nutrients that make wines that don’t have the fruit weight that I wrote of before, simply because they cannot gain the water and nutrients necessary to develop those characteristics. The amount of struggle the vine endures directly determines the wine’s weight, or lack of it.

It is ironic, that when we research the issues the catchphrases of wine describe, ie, the “vines must struggle”, or that a vineyard is “well-drained”, or the vineyards are “too wet to produce quality wine”, we see the simplicities, inaccuracies, or the shortcuts that those words cover up. Yet these catchphrases are so ingrained in wine writing, that we don’t even know to question them, or realize that they require significantly more nuance, or at minimum, point of reference. Yes, the vines on the upper-slopes are particularly well-drained. They do indeed struggle, sometimes to the point of producing vines are not healthy, and cannot the quality or the weight of wine that the producer (dictated by their customers) feels worthy of the price.

Extreme vineyard management

Blagny sous la dos d'Ane's shallow red soils produce a Pinot that is too light for the market to bear at the price it must be sold. photo: googlemaps
Blagny sous la dos d’Ane’s shallow red soils produce a Pinot that is too light for the market to accept – at the price it must be sold. photo: googlemaps

In Blagny, the Sous le dos d’Ane vineyard, which lies directly above the small cru of  Aux Perrières, has seen at least one frustrated producer graft their vines from Pinot Noir to Chardonnay. The Pinot, from the red, shallow, marly limestone soils, was felt to be unsatisfactorily light in weight. Not only would a lighter-styled, and minerally Chardonnay be well received, the producer will be able to sell it much more easily – and for more money because he could then label it as MeursaultSous le dos d’Ane, a much more marketable name.

Bel Air. More photos on this excellent website, and a terrific discussion in the comment section, albeit in French. Worth running through a translator. source: http://www.verre2terre.fr/
Bel Air. More photos on this excellent website, and a terrific discussion in the comment section. source: http://www.verre2terre.fr/

Producers in the Côte de Nuits rarely have the option to switch varietals. They typically must produce Pinot Noir to label as their recognized appellation. In the premier cru of Gevrey-Chambertin “Bel Air”, and Nuits St-Georges “Aux Torey”, growers have gone to the extreme lengths and expense of ‘reconditioning’ their plots. To do this, they must rip out their vines, strip back the topsoil and breaking up the limestone below. In the adjacent photo, a field of broken Premeaux limestone and White Oolite has been tenderized, if you will. The soil is replaced and the vineyard replanted. The entire process requires a decade before useful grapes can be harvested once again from the site, costing an untold number of Euros spent, not to mention the money not realize had the old vines been allowed to limp on. The same has been done in Puligny Folatières in 2007 by Vincent Girardin, and there again in 2011 by another unknown producer. Ditto with Clos de Vergers, a 1er cru in Pommard in 2009.

 

http://www.wineterroirs.com/2009/11/landscaping.html

click here: for the previous article, Understanding the Terroir of Burgundy: Part 3.2 The lower slopes

Understanding the Terroir of Burgundy, Part 3.1: The confluence of stone, slope and soil

Analysis: Combining what we know about limestone and soil, and applying that to a slope allows us to be predictive of topsoil makeup.

by Dean Alexander

slope comparison

Rise ÷ Run = Slope

It has always been my contention that the slope determines a vineyard’s soil type, and it is the soil type that is a major factor in wine character. Because many vineyards carry through the various degree of slope through the profile a hillside, the soils vary greatly from top to bottom. Water and slope work together to cause this. Rainwater both causes the development of clay on the hillside, and is the reason clay and other fine earth fractions will not readily remain on a slope. But lets start with a hillside typical of one found Burgundy, and the fractured stone and scree and colluvium that resides there.

Slope diagram
The 315 meter elevation represents a grand cru vineyard profile. The 350 meter profile represents a steeper rise which would be typical of a premier cru, which sits above a grand cru located on the curb of the slope. This added elevation and degree of slope, greatly changes the soil type at the top of the hill and decreases the soil depth, and at the same time increases richens and thickens the soil type, and deepens the soil in the lower grand cru section.

The typical Cote de Nuits hillside vineyard rises about 100 meters (328 feet). The base of many appellations sit at roughly 200 to 250 meters elevation, and here the vineyards are quite flat. As you move toward the hillside (facing uphill) it is common for there to be roughly a half a degree rise on the lower slopes. After 300 to 400 meters, the slope gently increases over the next 150 to 200 meters to roughly a 2 to 3 percent slope, where the grand crus generally reside. The upper slopes can rise dramatically in places, depending on the how wide the sections of bedding plates between faults, and pulled out and down with the falling Sôane Valley, and how much the edges of those bedding plates have fractured and eroded, also sliding down the hill. Areas like Chambertin, this slope remains moderate and the vineyard land remains grand cru to the top of the slope. However, above Romanee-Conti, the slope becomes much more aggressive, and the classification switches to premier cru at the border of Les Petits Monts. This uptick in slope, and the change in classification is common, but not universal in its application. As most things in Burgundy, there are a lot of exceptions to classification boundaries, notably for historical /ownership reasons.  

fractured limestone base exposed
If we were to strip away the fine earth fractions what we would expose is a fractured limestone base. Here the exceptionally shallow soil of Meursault Perrieres is peeled away and the limestone below is laid bare. The very shallow depth of soil, despite the relatively shallow slope suggests significant erosional problems.

Limestone derived topsoil types

If you could magically strip away all the dirt from the fractured limestone base of the Côte d’Or, leaving only a coarse, gravelly, sandy, limestone topsoil, and watch the soil development, this is what would happen: Over time, with rainfall, carbonization (the act of making the calcium carbonate solvent by carbonic acid in rainwater) would produce clay within the fractures of the stone. This new clay, is called primary clay (see Part 2.1) and gravity would have it settle to the lowest point in the crevices between the stones, below actual ground level. This primary clay will be rendered from weathering limestone everywhere on the Côte, from the top of the slope to the bottom of the slope, and tends to develop into a 9:1 to a 8:2 ratio of limestone to clay. This is the origin of limestone soils, and it is called… marly limestone.

Limestone to Clay diagram

 

limestone-clay diagram 2
I developed this diagram to express the different combinations and geological names of limestone mixed with clay and their agree upon percentages by the geological community. Marl dominates a full third of this diagram from 65 percent limestone/35 % clay to 65% clay / 35% limestone.

 

Marly Limestone – upper slopes: 90% to 80% limestone to clay

There are two common (and well-defined) terms that describe essentially the same soil type, applying different names and using differing parameters. This represents the purest, least mixed soil type on the Côte, and it is found on steeper (typically upper) slopes.

Clayey Limestone: the proportion of limestone in the mix is between 80% to 90% – source Frank Wittendal, Phd. Great Burgundy Wines A Principal Components Analysis of “La Côte” vineyards 2004) 

Marly Limestonecontaining 5-15% clay and 85-95% carbonate. source: The Glossary of Geology, fifth edition. (julia a. jackson, james p. mehl, klaus k. e. neuendorf 2011).

This is new, primary clay is not sorted by size, causing it to be rough in texture. Also of note, it is not plasticky like potters clay (kaolin clay) because of the irregularity of the particle size, which doesn’t allow its phyllosilicate sheets to stack, like it will once it is transported by water and reforms lower on the slope.

 

_______________

The Limestone to Clay diagram can virtually be tilted on upward and applied to the Côte to represent its topsoil makeup. The only part of it is missing is pure limestone because wherever there is limestone, clay has weathered from it.

It is no accident that you can turn this progression of limestone to clay into a general slope-soil diagram. The reason, as always, is water.
It is no accident that you can turn this progression of limestone to clay into a general slope-soil diagram. The reason, as always, is water.

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The fact that limestone and clay continues to exist in this 9:1 to 8:2 ratio (the stone does not continue to accumulate clay although it continues to develop it) allows us to deduce two things: First, the clay gains sufficient mass (depending on how close to the surface it is developing) where it can be eroded down the hill by rainwater runoff when it reaches roughly a 5% to 20% proportion of the limestone soil matrix. This static ratio also suggests that it exists only where erosion is a constant condition, meaning marly limestone can exist only on limestone slopes. It is erosion that maintains this general ratio of clay to limestone; limestone which will always produce primary clay as long as there is rainwater present. Of course, there may be other materials as well present in this mix, perhaps fossils, quartz sand, or feldspar.

I asked Pierre-Yves Morey, a noted winemaker in Chassagne, what was the texture, or the feel, of this marly limestone soil, is, and he described it simply as compact. “You would have to come to Burgundy and come see it.” I was looking for a little more richness to his description, but that is what I got. So… the definition of compact. The Glossary of Geology, 5th ed., defines compact (among other meanings) as “any rock or soil that has a firm, solid, or dense texture, with particles closely packed.” So there you have it. Clayey Limestone/Marly Limestone.

Argillaceous Limestone – mid-slope: 80% to 65% limestone to clay

The next incremental level of limestone to clay (75% to 25%) is not commonly cited, but sometimes referred to as Argillaceous Limestone or Hard Argillaceous Limestone. As a pure descriptor, this name isn’t especially helpful, since Argillaceous means clay. I also found another reference that called this ratio of limestone to “Mergelkalk” which is the German  for “marl chalk”, and this name indicates at least a progressive amount of clay over clayey limestone. This ratio of limestone to clay is not widely used, because, I suspect, it exists in the fairly narrow area of transition areas between marly limestone and Marl.

We might presume this ratio of limestone to clay appears not on the steeper slopes (generally above), but rather as the slopes grow more gentle, where to transported clay (from the steeper grades) may begin to flocculate as the rainwater runoff slows, adding to the primary clay growing in situ.

Because primary clay is more prone to erosion because of its mixed sized particles make its construction less cohesive, it is likely some of the primary clay developed in this lower location will be eroding further downslope, even as finer clay particles traveling in the rainwater runoff are starting to flocculate into transported clay in the same location.

With this high ratio of limestone to clay, it would be likely the be a compact soil, but because of the increased amounts of clay, not to mention some of it being transported clay, it will both have more richness and better retain water and prevent rapid evaporation.  Incidentally, his ratio of 75% limestone and 25% clay incidentally, is the recipe for industrially made Portland Cement.

Grand crus on compact marly limestone or argillaceous limestone: None

 

Marl – mid to lower slope: 65% to 35% limestone to clay

The beauty of, and the problem with, the word marl is its breadth of meaning. Marl as a term covers a wide variation of soils that contain at least some clay and some limestone, with many other possible components that may have been introduced from impurities on the limestone or from other sources within or outside the Côte.(1) But since we have magically stripped away the hillside, let’s imagine marl of its most simple combination: limestone and clay. Once the proportion of clay has risen to 1/3 of the construction with limestone, it is considered marl. It will continue to be considered Marl until clay exceeds 2/3 of the matrix. This is the definition established by the American geologist Francis Pettijohn 1957 in his book, Sedimentary rocks (p410).

Marl is an old, colloquial term that geologists may not have completely adopted until fairly recently. Perhaps it is because of this, that the definition of marl has an uncharacteristically wide variance in meaning, can be applied to a fairly hard, compact limestone soil, to a loose, earthy construction to a generally fine, friable, clay soil.  I imagine that on the clay end of the marl spectrum, the soil begins to become increasingly plasticky, due to the increasing alignment of the clay platelets by the decreased lime in the soil. This is purely subjective on my part.

Marl is most often noted in the same positions on a slope as colluvium, at a resting place of not much more than a 4 or 5% grade.  To attain a concentration of clay of at least 1/3 (the minimum amount of clay to be marl) rainwater runoff must slow enough for the clay’s adsorptive characteristics to grab hold of passing by like-type phyllosilicate minerals and pull them out of the water passing over it. As you can imagine, in a heavy deluge, with high levels of water flow, this will only happen lower on the slope, but in light rain, with a much less vigorous runoff, this will occur higher on the slope. How far these clay mineral travel down the slope before flocculation all depends on the volume of water moving downhill, and its velocity, which tends to be greatest mid-slope.

We can safely deduce that the first marl construction on our magically stripped slope consists of 15% primary clay (maximum) because that is what we started with, 20% transported clay which has been adsorbed to the site, and 65% limestone rubble (rock, gravel, sand and silt). Here, the ratio of stone in the topsoil is lower than in the slope above, because the topsoil is deeper, and the stone represents a small proportion of the ratio. Additionally, it is very possible that some of the primary clay, which is more readily eroded, may have been washed further downslope, in which case the percentage of transported clay would actually be higher.

It also stands to reason that the soil level is significantly deeper where marl resides by a minimum of 15%, due, if only because of it’s increased volume of clay to those soil types above if the limestone concentration in the soil remains constant from top to bottom.  Of course, we know that fracturing of the limestone, erosion and gravity have moved limestone scree downslope.  If you could know that volume of additional limestone that had accrued on the slope, and then factor in the percentage of clay, you could effectively estimate the soil depth. Farther down the slope, marl with 65% clay to 35% limestone, we can assume to have a minimum of 30% deeper soil levels, but again, that depends on the limestone scree that has moved downslope as well. Notes of excavations by Thierry Matrot in 1990 in his parcels of MeursaultPerrières show one foot or less topsoil before hitting the fractured limestone base, whereas his plot of Meursault-Charmes just below it, was excavated to 6 feet before hitting limestone.(3) This indicates, a significant amount of limestone colluvium had developed in Charmes (some of which may have been the overburden removed from the quarry at Clos des Perrières?) that has mixed with transported clay to attain this six-foot depth of marl dominated soil.

Wittendal’s work analyzing the vineyards of Burgundy (2004) revolved around statistical methods tracking values of slope and soil type, among other 25 other factors. From that, he plotted the vineyards as data points to try to develop trends and correlations. I was not surprised by his results, as it confirmed many of my assumptions about slope causing the types of soils that develop there. Of note, though, to some degree, his work dispels some of the assertion that marl/clayey soils reside more in Beaune and limestone/colluvium soils reside primarily in the Nuits.

Wittendal plots a perfect 50-50 marl to colluvium, as point zero in the center of a four quadrant graph (Figure 8 – The Grands Crus picture components 1 & 2). On the left side of the graph would be the purest expression of marl. This represented as negative four points of standard deviation ( σ ) from zero (the mean). On the right, the purest representation of colluvium is four points positive of standard deviation ( σ)  from zero (the mean).

Grand Crus on marl soils: more than one standard deviation (neg)Corton Charlemagne (one section with a standard deviation of -3.5, and another section at -1.5 )  Chevalier-Montrachet -1.75.

Grand Crus Primarily on marl soils with some colluvium: near one standard deviation (neg). Only one lower section of the Pinot producing Corton has a surprising amount of marl – the vineyard is not named (-1.25 ) and Le Montrachet with a surprising amount of colluvium (-.8 )

Grand Crus on slightly more marl than colluvium: Romanee-Conti sits on slightly more marl than the mean  (-.3), La Tache sits right near zero.

Grand Crus on slightly more colluvium than marl: less than one-half the standard deviation. Musigny, Bonnes Mares and Ruchottes-Chambertin. (.333)

 

Ruchottes inclusion here is at first surprising. But since there appears to be little chance of colluvium to develop on this upper slope, coupled with its shallow soils, it is this soil construct makes sense. In fact, this highlights that Wittendal’s work represents the ratio of marl to colluvium, rather than the depth of marl and colluvium present.  It is my contention that the most highly touted vineyards have significant soil depth and typically have richer soils. Ruchottes, which many have suggested should not be grand cru, has little soil depth (which is a rock strewn, quite compact marl), and the vines there can struggle in the little yielding Premeaux limestone below. A vine that struggles, despite all of the marketing-speak of the last two decades, does not produce the best grapes.

 

Clay Marl – lower slope: (a subset of marl)

Clay marl seems to be within the defined boundaries of Marl. One would suspect this to be in the 35-45 limestone with the remainder being clay. It is described by the Glossary as “a white, smooth, chalky clay; a marl in which clay predominates.” No specific ratios are given.

Marly Clay – lower slope 15% carbonate 

Marly Clay, and also referred to as marly soils are 15% carbonate and no more than 75% clay. At this point, it seems the use of the word limestone has been discontinued. Perhaps at this level we are dealing with limestone sand sized particles and smaller, perhaps with pebbles. There must be silt and clay sized limestone particles before complete solvency, but I have never seen mention of this. It is likely the carbonate is solvent, influencing, and strengthening the soil structure, and affecting to some degree, clay’s platelet organization? As much as I have researched these things, I have never seen this written. The soil just is the soil at this point.

Deceptive here is the need to discern limestone sand from quartz or other sands. Limestone sand will be “active” meaning it would be releasing significant calcium carbonate into the soil (disrupting the clay’s platelet alignment) and would be actually be considered marl. I imagine the degree of plasticity to the soil would be the shorthand method to determine this, although I understand if you pour a strong acid on a limestone soil, it will visually start carbonization (fizzing).

Could it be, that in marketing of limestone as the key factor in developing the legend of Burgundy, the Burgundians may have swept the subjects of claystone and shale under the rug?

 

Clayey soils – Sôane Valley fill 

Worldwide, most clayey soils develop from shale deposits. Geologist Francoise Vannier-Petit uses the word shale to explain clay to importer Ted Vance in his writing about his day with her. In fact, she virtually used the term clay and shale interchangeably. However, other than that writing, I have never seen the word shale used in Burgundy literature. This might lead one think that shale is not existent on the Côte. Clayey soils are a large component of the great white villages of the Côte de Beaune however, and ignoring shale as a major source of this clay may be a mistake. Vannier does mention alternating layers of limestone and claystone in Marsannay in the marketing material the Marsannay producer’s syndicate produced which I discussed at length in Part 1.3.  Could it be, that in marketing of limestone as the key factor in developing the legend of Burgundy, the Burgundians may have swept the subjects of claystone and shale under the rug?

 

Clayey sand and loam (no carbonate)

We've seen this before, under the guise of the USDA soil diagram. Here is the original by Francis P. Shepard
We’ve seen this before, under the guise of the USDA soil diagram. Here is the original by Francis P. Shepard

Wittendal uses “Clay with silicate sand” as one defining soil type in his statistical analysis of Burgundy vineyards. He does not give a percentage breakdown he is using for this soil type. However, reaching again to the Glossary of Geology, the most straightforward of definition is attributed to Geologist Francis Shepard: An unconsolidated sand containing 40-75% sand 12.5-50% clay and 0-20% silt.’ (Shepard 1954)“. Unconsolidated means that it is not hardened or cemented into rock. Of note: the definition attributed to Shepard is slightly at odds with the diagram to the right which Shepard is most known for, which has clayey-sand contains no more than 50% clay. The definitions of clayey-sand and loam clearly overlap. At one extreme, Clayey-sand can also be defined as a loam.

Clay-loam – clay sand

Clay-loam is a soil that contains clay (27-40%),  sand (20-45%), with the balance being silt, all of which have very different particle sizes. If you apply the lowest percentage of clay 27%, and a high percentage of sand 45%, and the remainder, silt at 28%; this combination doesn’t somehow doesn’t seem to fit the description well. Clay-sand is overlapping with clay-loam but generally consists of 60% sand, 20% silt and 20% clay.

Clayey-silt

Clayey-silt In 1922 geologist Chester Wentworth defined grain size. Clayey-silt thusly is 80% silt-sized particles, no more than 10% clay (which particles are substantially smaller), and no more than 10% coarser particles of any size, though this would be primarily of sand-sized and above.  Conversely, Francis Shepard’s definition of clayey silt in his 1954 book, is 40-75% silt, 12.5-50% clay and 0-20% sand. 

*Grand Crus on clayey soils: None

Colluvium, Breccia – mid to lower slope (and Scree – everywhere)

The scree filled Les Narvaux in Meursault. photo: googlemaps
The scree filled Les Narvaux in Meursault. photo: googlemaps

Colluvium and breccia are very similar. They are both rubble that has amassed on a resting place on a slope.

Breccia has a more specific definition, being at least 80% rubble and 10% clay, and can be loose or like any soil type, become cemented into rock. Incidentally, that 10% clay ratio has come up again, because just as the marly limestone I spoke of before, the stone will weather primary clay, but rainwater erosion consequently will remove it as the clay gains mass. The stones that form these piles are what geologists refer to as angular because they are fractured from larger rock, they have angular or sharp edges. This remains true until the stone has become significantly weathered by the carbonic acid in rainwater.

Colluvium, on the hand, is a construction of all matter of loose, heterogeneous stone and alluvial material that has collected at a resting place on a slope, or the base of a slope.  These materials tend to fall, roll, slide or be carried to the curb of the slope as scree (those loose stone that lies upon the surface) or washed there by runoff. In Burgundy, the rocks of colluvium and breccia are likely mostly limestone.

Rocky soils, such as colluvium and particularly breccia, are less prone to compaction because of the airspace is inherently formed between the rocks as they lay upon one another. This protection against compaction should not be overlooked as a major indicator of vine health and grape quality these colluvium sites provide. Drainage through a rocky colluvium surface material can be, let’s say, efficient, and this too is a natural defense against soil compaction, because a farmer must be cautious about trodding on wet soils because they compact so easily. Chemical weathering will develop primary clay deposits amongst the stone, and the stones themselves will slow water as it erodes down the hill, likely giving this primary clay significant protection from erosion.

Grand Crus on colluvium soils more than one standard deviation. With the most colluvium are the vineyards of Clos Vougeot with a range of σ ( 2 to 2.7) and Romanee St Vivant (1.8). followed by Most of the red vineyards of Corton sit largely on colluvium (1.25 to 1.75) Echezeaux (1.1).

Grand Crus on colluvium but with more marl: within 1 standard deviation. Charmes, Latricieres, and Richebourg form a cluster of vineyards with a σ of  (.5 to .75) with just a little more colluvium than the Musigny, Bonnes Mares and Ruchottes all at roughly a σ of .4.   source Wittendal 2004 (figure 8)

Here we find some interesting groupings. First, the grand crus with the most colluvium are generally considered in the second qualitative tier. The outlier there would be Romanee St-Vivant, which while great, is not considered to be in the same league as Vosne-Romanee’s other great wines, Romanee-Conti, La Tache, and depending on the producer, Richebourg. Are high levels of colluvium cause the vines more difficulty than those planted to vineyards with a heavier marl component?

Colluvium Creep and landslide, in this case at Les Rugiens in Pommard. The steep slope being Rugiens Haut, and in the foreground, its benefactor, Rugiens Bas. Here is an example of two vineyards that should be separated in the appellation, but both are labeled as Rugiens.

But this question rolls back to ratios of how much colluvium there is in relation to how much marl is in that location, what is the ratio to clay to limestone in the marl at each site (which would change the placement of zero (which would change the mean), and lastly, at what point is it no longer colluvium but marl or vice-versa?

Colluvium Creep

Colluvium is known to creep, meaning it continues to move very slowly downslope since it is not anchored to the hillside bedrock, rather it rests there. It is not uncommon to see the effects of this creep in tilted telephone poles and other structures on hillsides. Creep is essentially a imperceivably slow landslide. The most obvious creep/slide in Burgundy is the slope of Rugiens-Haut onto Rugiens-Bas, in Pommard.  Gravity, being what it is, nothing on a slope is static, and colluvium will, so very slowly, creep.

 

 


 

Authors note:

What I write here, is a distillation of the information laid out in the previous articles, and my weaving together all the information to build a picture of the various soil types and the slopes that generate them. Much of this is my own analysis, cogitation, and at perhaps at times conjecture, based on best information. 

As I mentioned my preface, I had come to some of these conclusions when researching vineyards for marketing information and noticed a correlation between slope and soil type.  The research that formed the basis of the previous series of articles, was done to see if the science of geology supported my theory that a vineyards position dictates the soil type there. I think it does.  Ultimately the goal of these articles is to lay down a basis for explaining and predicting wine weight and character, independent of producer input, based on a vineyards slope and position.

Where science generally begins and ends are with the single aspect of  their research.  That is the extent of their job. Scientists rarely will connect the dots of multiple facts for various reasons. It can move them outside their area of examination, or it may not have a direct evidence to support the correlation, or the connection of facts may have exceptions. The study of the cote is clearly would b a multi-discipline enterprise. There is no cancer to be cured, no wrong to be righted, and no money to be made off of understanding it’s terroir. So it has been largely left to the wine professional to ponder.  These are my conclusions. I encourage you to share yours.


 

(1 & 2) Vannier-Petit discusses alternating layers of Claystone and Limestone in Marsannay. While I have never read this of the rest of the Côte d’Or, the Côte has never been examined as closely as Vannier-Petit is beginning to examine it now. Layers of claystone may well exist, and given the amount of clay in the great white regions, this may well be the case.

(3) Per-Henrik Nansson “Exploring the Secrets of Great Wine” The Wine Spectator, Oct. 25, 1990

Note: Sediment gravity flow has four principle transport mechanisms. From wikipedia

  • Grain flow – Grains in the flow are kept in suspension by grain-to-grain interactions, with the fluid acting only as a lubricant. As such, the grain-to-grain collisions generate a dispersive pressure that helps prevent grains from settling out of suspension. Although common in terrestrial environments on the slip faces of sand dunes, pure grain flows are rare in subaqueous settings. However, grain-to-grain interactions in high-density turbidity currents are very important as a contributing mechanism of sediment support.[4]
  • Liquefied/fluidized flow – Form in cohesionless granular substances. As grains at the base of a suspension settle out, fluid that is displaced upward by the settling generates pore fluid pressures that may help suspend grains in the upper part of the flow. Application of an external pressure to the suspension will initiate flow. This external pressure can be applied by a seismic shock, which may transform loose sand into a highly viscous suspension as in quicksand. Generally as soon as the flow begins to move, fluid turbulence results and the flow rapidly evolves into a turbidity current. Flows and suspensions are said to be liquefied when the grains settle downward through the fluid and displace the fluid upwards. By contrast, flows and suspensions are said to fluidized when the fluid moves upward through the grains, thereby temporarily suspending them. Most flows are liquefied, and many references to fluidized sediment gravity flows are in fact incorrect and actually refer to liquefied flows.[5]
  • Debris flow or mudflow – Grains are supported by the strength and buoyancy of the matrix. Mudflows and debris flows have cohesive strength, which makes their behavior difficult to predict using the laws of physics. As such, these flows exhibit non-newtonian behavior.[6] Because mudflows and debris flows have cohesive strength, unusually large clasts may be able to literally float on top of the mud matrix within the flow.
  • Turbidity current – Grains are suspended by fluid turbulence within the flow. Because the behavior of turbidity currents is largely predictable, they exhibit newtonian behavior, in contrast to flows with cohesive strength (i.e., mudlfows and debris flows).[6] The behavior of turbidity currents in subaqueous settings is strongly influenced by the concentration of the flow, as closely packed grains in high-concentration flows are more likely to undergo grain-to-grain collisions and generate dispersive pressures as a contributing sediment support mechanism, thereby keep additional grains in suspension. Thus, it is useful to distinguish between low-density and high-density turbidity currents.[4] A powder snow avalanche is essentially a turbidity current in which air is the supporting fluid and suspends snow granules in place of sand grains.

Understanding the Terroir of Burgundy, Part 2.2: Soil formation

We all know what soil is, or at least we think we do. If I were to ask you what was in soil, what would you say?

by Dean Alexander

In healthy soils, minerals typically only represent slightly less than half of the volume of soil, while air and water incredibly represent much of the rest. Here is the soil of La Tache in Vosne Romanee.  photo: leonfemfert.wordpress.com

Soil: 45, 25, and 25%

Despite all the talk about limestone, to really understand the terroir of Burgundy, we really have to understand what soil is and the material from which it is eroded. The mineral component, or the part we think routinely of as soil, are typically only 45% of the soil matrix. The balance is actually 25% air, and a further 25% of water, with the last 5% being split between humus (4%), roots (.05% ), and organisms (.05). It would make sense that this percentage changes seasonally, depending on how much water is in the soil from rainfall (or the lack of it) which changes the ratio of minerals, water, and air. Further, these ratios can change based on soil compaction, which decreases the air in the soil, which in turn increases the percentage of the mineral and organic component.  Why is this important? Because this is the environment that the vines live and they require a certain ratio of each of these components to produce high-quality grapes.

Cote soil influencers
I developed this graphic to illustrate the assorted soil formation processes that affect the Côte, and are described in depth in Limestone Fracturing in Part 1.2, and from Limestone to Clay in part 2.1, in earlier articles in this series. This article, Part 2.2 Soil Formation, builds upon those earlier concepts.

 The 45%: Burgundy’s mineral makeup

The French refer to the loamy Saône Valley fill as Marne des Bresse. The earth there is very deep, and typically is too wet for high-quality grape production. Historically this been used for pasture land for sheep and cattle. With every storm, this rich loam from the valley intermixes a little bit more with the soils of the boundary vineyards, and even encroaches on the loose, stony soils of the Côtes lower slopes.  ‘Interfingering’, was how geologist James E. Wilson described this mixing of soils in his 1990 book, Terroir: The Role of Geology, Climate, and Culture in the Making of French Wines.

Bore samples, according to Wilson, had indicated that this interfingering has reached westward, up the hill, to influence the soil construction of the lower sections of the grand cru Batard-Montrachet. With this information, he inferred that the Saône fault must be near.  It is notable that in 1990 precise location Saône fault was not known, and around Puligny, it still may not be. I suppose the wealthy Puligny vintners have no need to explain why Puligny-Montrachet is great. Vannier-Petit however, does tacitly show the Saône fault in her map of Gevrey, which is represented by the abrupt end of the limestone bedding east of RN74.

The ravine Combe de Lavaux defines character of most of the premier crus of Gevrey-Chambertin, but more importantly, its alluvial wash greatly expanded the growing area of vineyards below the village. Click to enlarge
The ravine Combe de Lavaux defines the character of most of the premier crus of Gevrey-Chambertin, but more importantly, its alluvial wash greatly expanded the growing area of vineyards below the village. Click to enlarge

Because the Côte is an exposure of previously buried, older limestone, younger soils line the divide on either side of the escarpment. The Saône Valley’s Marnes de Bresse brackets the Côte on the eastern, lower side of the slope, while younger rock and soil material that cover the tops of the hills, to the west, and beyond.

From the hilltops above, those younger soils have eroded down, bringing feldspar and quartz sand, silt, as well as phyllosilicate clay minerals, to help fill in and strengthen the rocky limestone soils of the Côte. In many places, geological faulting, coupled with runoff or streams, have created combes or ravines which have allowed substantial alluvial washes to extend the planting area of the Côte. A prime example of this is the Combe de Lavaux which is a dominate feature of the appellation of Gevrey-Chambertin.  It has sent a large amount of alluvial material around and below the village of Gevrey, creating good planting beds for village-level vineyards. Alluvial soils are nothing more than a loose assortment of uncemented of soil materials that have been transported by rain or river water. These materials are typically sand, silt, and clay, and depending on the water flow, various sizes of gravel particles. It is this sand and gravel that has traveled with the water flow from the Combe, that provides these vineyards that protrude past the limestone of the escarpment the drainage the vines require.  These are not, however, the soils that will produce the great premier cru, or grand cru, wines for which Burgundy is famed.

a graded sediment bedSoil suspension and graded bedding

Soil moves downslope by water erosion, the force of gravity, and even is transported by the force of significant wind. With movement, the particles within the topsoil are in a state of suspension. Geologists refer to this movement and suspension as turbidity. Because of their weight, gravel travels downward in the moving soil, creating a progressively sorted soil, with coarser pieces on the bottom, while the finer particles find their way to the top.  The result of this is called a graded sediment bed. (1)

While it is easier to see how a graded bed might be created in a stream bed below a ravine like the Combe de Lavaux, I was somewhat perplexed how this might occur in Alex Gamble’s Les Grands Champs vineyard in Puligny-Montrachet, see Clay part 2.1.  Here gravel bedding lay at 80cm, a little more than two and a half feet below the surface. Above the gravel, sat a foot and a half of heavy, yellow, clay-dominated soil. This was, in turn, topped by nearly a foot of loamy-clay soils. Vannier-Petit estimated these soil horizons, as geologists refer to them, were created between two and five million years ago by water runoff. What kind of run off?  I realized that the kind of runoff that creates graded bedding happens often, like in this photo (below), taken in Pommard during the winter/spring of 2014, by winemaker Caroline Gros Parent.

This is how graded bedding develops.
This is how graded bedding develops. Here the road to Pommard has flooded in the winter storms of 2014. Photo: Caroline Parent via twitter

Parent material

Geologists talk about a soil’s parent material because every element of soil came from a different material, which was then weathered, both mechanically and chemically, into various sizes. These minerals will then accumulate, either poorly sorted into an aggregate material, or they can be well sorted by the wind, water, or gravity into size categories. Sand and silt are generally said to have been created by mechanical weathering, although chemical weathering is always a present force, as long as there will be rain. Sand can be made of any parent rock material, but in Burgundy, there are sands made of granite, in addition to plentiful limestone sand. (2) We know this because there is loam present (as well as graded bedding), in the Grands Champs vineyard from the Saône valley fill below. The water that carried this non-limestone, Côte-foreign material, would have carried quartz sand with it as well when it created the graded bedding there. This gives us a very important insight into the construction of the soils of Burgundy.

Fine earth fractions

Fine Earth Fractions are the trinity of sand, silt, and clay. Gravel and sand can be made of limestone or other rock that has been weathered into smaller and smaller pieces, but silt is typically feldspar or quartz. Clay is much, much smaller in size, and is created by chemical weathering of rock. Its parental material can be limestone, granite or other stone.

Geologists grade soil minerals by size; the basis of which are particles that are 2 mm and smaller. These are called fine earth fractions and consist of sand, silt, and clay. In equal thirds of each of the three soil fractions is considered perfect for farming crops, and is termed loam. The various sizes of minerals in the soil makeup gives the soil its texture.

Clay, we have talked about in length in part 2.1, and differs from silt and sand because it is a construction from stone that has been chemically weathered, whereas silt and sand are derived from mechanically weathered rock. Additionally, clay is a construction of clay minerals that are bound with aluminum and oxygen by water and carries minerals within its phyllosilicate sheets. It is also important to mention that clay’s particles are considerably smaller in diameter, being less than 2 microns in size.  Soils with more clay hold more water,  so they require less frequent application. An overabundance of water in clay soils causes oxygen depletion in the root zone.  This can limit root development.  The abundant solvent calcium in the limestone soils Burgundy misaligned the clay platelets, loosening the soil, and allowing better drainage.

Diatoms (top) and Radiolarians bottom, fill the ocean floors with sediment.
Diatoms (top) and bottom, fill the ocean floors with sediment.

Silt is specifically formed from quartz and feldspar, and is larger than clay, being 0.05 mm-0.002 mm. We know that any feldspar in the soil, could not have come from weathered stone; neither limestone or granite, which was the dominant stone in the area when the limestone beds were forming, because it would have metamorphosed into a phyllosilicate clay mineral if it had. This means the feldspar has traveled onto the Côte, either from above or below the limestone strata.

While it might seem logical to assume the quartz in silt originated in the earth’s crust, and perhaps degraded from granite that was prevalent in the area, this may not be the case. The first problem is quartz is resistant to chemical weathering. And physical weathering like frost wedging of sand particles may continue to yield results beyond a certain size.

Researchers from the University of Texas at Arlington used (and I cut and pasted this) a “backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe.” They found that the 100% of silt quartz found in 370 million-year-old shales of Kentucky were made from the “opaline skeletons” of plankton, radiolarians,  and diatoms. This, they reasoned, might explain the lack of these kinds of fossils during the same period. These tiny animals had all been incorporated into the then forming shale. This may also be the case for the silt quartz of Burgundy, itself too having once been a Jurassic, seaside resort. This, in fact, this information also suggests this quartz silt may come from weathered shale that is much older than the limestone of the Côte.

A sandy soil horizon
A sandy soil horizon

Sand is larger than silt. being less than 2 mm, and typically is constructed of quartz or limestone particles. The limestone sand will weather to solvent calcium carbonate, but the quartz will not weather and will remain as sand. It is likely that significant quartz sand has been washed down from the hillsides, and certainly is a major contributor to alluvial soils below the combes. Sand drains so quickly that vines grown in sandy soil have more frequent water requirements, but require a lesser amount of water.  Adequate water maintains plant growth while minimizing the loss in the root zone.

 Plant and animal soil contributors

Grasses, with their dense root systems, are positively impactful to the topsoil. In their decomposition, darker soils are created to deeper depths, and the resulting soils also tend to be more stable.  In a monoculture of grapevines, many growers are finding this to be a significant advantage. In Australia, some grape growers are using grasses to help lower soil temperature in efforts to slow down ripening in an ever-warming climate.

Much is made by those practicing sustainable and organic cover crop encourage populations beneficial predator insects and birds, but grasses and cover crops also encourage subsoil organisms and microorganisms growth as well. Most common are bacteria and actinomycetes (rod-shaped microorganisms), which by weight have been found to be four times more present by weight than earthworms in healthy soils. While these are important to the quality of the wine, they are only an intricate part of terroir if it is practiced by the farmer.

The 25%: Air (and soil compaction)

Soil compaction relates to poor water infiltration and low oxygen levels. drawing: landscaperesource.com
Soil compaction relates to poor water infiltration and low oxygen levels. drawing: landscaperesource.com

The proper amount of airspace between mineral fragments is very important for vine growth and allow for water to penetrate and be retained by the soil. Soils with diminished airspace are said to have soil compaction, and compaction is difficult to correct once it has occurred. The Overly tight spacing between the mineral component of a soil restricts oxygen levels and contributes to a poor water holding capability.  Rainfall itself can cause some soil compaction, but most commonly walking or operating farming equipment on moist soils does the most damage. In drought years, soil compaction can lead to stunted vine growth and decreased root development. In wet years, soil compaction decreases aeration of the soil and can cause both a nitrogen and potassium deficiency. Additionally, without adequate porosity to the soil, water cannot easily penetrate the soil during a rainstorm. Water that cannot infiltrate soils of flat terrain can stagnate, which further compacts the soil,  or on sloped terrain will runoff, which can create erosion problems.

Positive effects of moderate compaction

As moisture of the soil increases, so does the depth of compaction.
As moisture of the soil increases, so does the depth of compaction.

Moderate compaction can have some desirable effects. Moderate compaction forces the plant to increase root branching and encourages secondary root formation. This additional root growth is the plant’s response to not finding enough nutrients with its existing root system. Plants with more extensive root systems are more likely to find nutrients that are not carried by water, like phosphorus.  Obviously, more compaction is not better, because it impedes root growth, lessens the oxygen in the soil, and repels water from penetrating the soil.

While deep tillage 10-16 inches can shatter the hard packed soil, studies have shown that crop yields will not return to normal following the effort. While there are factors that might cause the soil to return to compaction, like a farmer, unintentionally re-compacting their soils, more than likely tilling does not return the airspace that was lost in the soil itself. Further continuous plowing and tilling at the same depth can cause serious compaction problems on the soil below the tilling depth.

The 25%: Water (the key to everything that Burgundy is)

It should be impossible to talk about soil without talking about water, given it is optimally 25% of soil’s makeup. It is certainly tempting to pass over the subject of groundwater and lump it into erosion, but that would really shortchange our understanding of the Cote. Part of Burgundy’s success can surely be attributed to relatively steady rainfall year round, coupled with the fractured limestone’s ability to hold water until its reserves of water which is held within the stone can be recharged by future storms.

Good drainage, well-drained? Let’s reset the dialogue.

The infiltration of rainfall by the soil is the first and perhaps most important factor in recharging groundwater levels. Like I wrote of compaction, the soil has to be porous enough to penetrate the topsoil and subsoils successfully. The buzz word in the wine world is drainage, with terms like well-drained, and good drainage appearing often. I suppose we picture the roots drowning in mud if there isn’t good drainage. But the idea of good drainage really simplifies the issue. Drainage can have to do as much to do with compaction as soil materials or slope. Soil drainage is important in fighting erosion as well not causing additional soil compaction. Good drainage, which is what happens with a well-aerated soil, allows the vines roots sufficient oxygen and nitrogen and allows the roots to take in nutrients like phosphorous and potassium. But none of this can happen if the soil releases rainwater too quickly, and the vine can perform none of these vital tasks. The reality is, it is not the fact that a soil well-drained, but rather it drains at the adequate rate for a given rainfall. Obviously, this will not always be a perfect equation since rainfall varies greatly depending on the year and the time of year.

The speed of drainage

water movement through various soil types. source: usda-nrcs
Water movement through various soil types. source: USDA-nrcs

The kinds of materials that make up the soils contribute greatly to the rate of water ability percolate through the material. The speed of the mater’s movement depends on the path the water is channeled in. The most direct path that is in line with gravitational pull will give the fastest drainage.

Water movement comparison through sand and clay. Soure Coloradostate-edu.
Water movement comparison through sand and clay. Source Coloradostate-edu.

Sandy soils, as one might expect, drains quickly because it consists of only slightly absorptive, small pieces of stone, that allow the water to essentially slide right past.

Clay, on the other hand, is very dense and plasticity. These characteristics, as you might expect, would be resistant to allowing water to pass through, and large bodies of transported clay can redirect horizontally, the flow of water percolating through from above due to it’s slower absorption rate. But what isn’t obvious is that clay’s construction encourages capillary action. The clay body will distribute water throughout its mass, counter to gravitational pull, becoming completely saturated, before releasing excess water through to the material below.

Argillaceous Limestone
Argillaceous Limestone with its horizontal fracturing slows water percolation. click to enlarge

Highly fractured limestone that is still in place, is often is fragmented in a prismatic pattern. However some limestones, like this soft argillaceous limestone to the right, with its high clay content, may fracture horizontally. The type of fragmentation would depend on the stresses upon the stone, the freeze-thaw effects of water and temperature, as well as the material of the stone’s construction. Clay based stones will tend to fragment horizontally and when they do, they are considered platy, and water will percolate more slowly than stones that fracture in a prismatic fashion.

Water movement through soil
The hillside of the Côte is a recharge area for water collection, while the valley below is a discharge area, where excess water is expelled. The water table is at the capillary fringe. Water uses faults and fissures to move quickly into and out of the saturated zone. It is likely there are aquifers, meaning caves which have been cut out of the limestone by carbonization below the Côte, where the water is stored.

 

a small karst aquifer Photo:planhillsborough.org/
A small karst aquifer in Florida. Photo:planhillsborough.org/

Groundwater, the water table, and karst aquifers

In writings regarding Burgundy, very little is said about ground water, other than there are no cellars built underground in Puligny because the water table is too high there. A plentiful water supply may be one of the features that propel the vineyards of Puligny into the ranks of the worlds best. As my diagram above shows, water percolates through the soil and stone. This upper section is called the vadose zone, or unsaturated zone. Slabs of limestone, fissures, faults, and clay bodies all can change the course of the water flow. Each horizon of soil and each layer of stone have their own rate of percolation. With this much limestone, it is very likely there are karst aquifers or large caves caused by the carbonization of calcium carbonate beneath the Côte, but I could find no specific mention of aquifers in close proximity to the Côte. There is a mention in a European Academies Science Advisory Council‘s country report for France, that in Burgundy there are “karsified Jurassic limestone layers” somewhere in the region, but nothing more is elaborated upon.

There is a very famous and massive karst aquifer with seven very deep layers that spans from north of Burgundy across the Paris basin to the English channel. The deepest level of water is brackish. The uppermost section is called the Albian sands sits at than 600 meters, and was first was drilled into in 1840 taking well more than 3 years to achieve. The water there is 20,000 years old, and there has been discussion whether the water should be considered fossil, meaning there is a question whether there recharge from the water above, or not.

 

Next up: Understanding the Terroir of Burgundy, Part 3: Confluence of stone, soil, and slope

 


 

(1) Interestingly, larger stones, especially the flatter, rounded shaped stones that the French refer to as galets, tend move to the surface, probably because of their larger displacement values.

(2) Sand from other parent rock material is likely to be available as well.

Understanding the Terroir of Burgundy: Part 2.1 From Limestone to Clay

© BiVB Latricieres
Latricieres under brewing storm clouds.  photo © BiVB

by Dean Alexander

The weathering of limestone: let it rain

flooding
Rain and Flooding

For the past 35 million years, rainwater has endlessly and relentlessly washed across the limestone escarpment. To varying degrees, the limestone will absorb water through its pores, but stone that has been damaged by ductile deformation is much more easily infiltrated. Faster still, water fills the cracks and fissures created by geologic strain, finding freshly broken calcium carbonate to wetten, and begin the process of chemical weathering called carbonation.

Rain rainwater, it seems is more than just H2o.  From the storm clouds above, H2o binds to with carbon dioxide (CO2) to form carbonic acid (H2CO3). And although carbonic acid is typically a mild acid when carried by the rainwater, it does slowly act as a solvent to the calcium carbonate (CaCO3) that holds the limestone together. This carbonation frees the carbonate from the calcium, and will metamorphose the calcium into calcium hydrogen bicarbonate Ca(HCO3)2, which technically only exists in solution. (1)  The material that remains behind once it is no longer bound by bonds of the stone, is whatever impurities that were in the stone when it formed. This could include clay, fossils, feldspar which is the most common mineral on earth), among many other possibilities.

Nature’s Highly Engineered, Deconstruction of Limestone

Calcium Bicarbonate photo credit: Frank Baron/Guardian
The calcium carbonate in limestone is made solvent by the carbonic acid in rainwater.  The calcium carbonate is metamorphosed into calcium hydrogen bicarbonate  or Ca(HCO3)2. Technically calcium bicarbonate exists only as a water solution. As long as enough CO2 remains in the water, calcium bicarbonate is stable. But once excess Co2 is released, calcium carbonate is dropped out of solution resulting in the scale like on the facet above. photo credit: Frank Baron/Guardian

Calcium carbonate is more soluble in colder temperatures.  If you aren’t paying attention, this, along with so many other pieces of information might seem fairly unrelated. But like everything else, it is an important piece of the puzzle. It is all part of nature’s finely detailed engineering, where every element directly is related to, and influences the next.

This fact that calcium is more soluble in colder temperatures folds beautifully together with the freeze-thaw fracturing of the limestone that I detailed in Limestone: Part 1.2. The acidic water enters the more porous limestone, where it then freezes. This exerts immense internal pressure on the rock, which causes it to split along the pores, can cause various types of fractures within the stone.  Then when the acidic ice within the rock begins to melt, it erodes the stone along the fissures, being aided by the cold temperatures. The more acidic the rainwater, the more minerals the groundwater can dissolve and be held in solution. Interestingly, because lime is alkaline (a base as opposed to acid) it naturally balances the ph of the water, and thus the soil, which is good for the health the vines.

Clay Development = great vineyards

Puligny excavation at Alex Gamble
An excavation of the village cru, Les Grands Champs by Alex Gamble and Francoise Vannier-Petit. According to Vannier-Petit’s analysis, below the first 30 centimeters of dark clay-loam soil, lies a fine-grained, yellow clay. In its most pure form it is typical of transported clay being less than 2 microns, before mixing with heavier soils of increasing size down to an 80 cm depth. Here it transitions to more loosened substratum of “angular gravel” of 2 mm in size, which she also terms “heterometric stones”, providing good drainage for the site. See more at alexgamble.com
Les Grands Champs
Visual observation: Les Grands Champs is located on the eastern edge of the village of Puligny. The land here is be quite flat, with less than a one percent grade.  It sits at the foot of the 1er cru Clavillions (where the road turns to head up hill). Folatieres lies just above that, the bottom of which is denoted by the by the plot being replanted.

Every Burgundy vineyard that is considered to be great has at least some clay and some limestone in their makeup. But that is not surprising since  clay, is the byproduct of the chemical weathering of stone. The silicate materials (essentially the building blocks almost all minerals) in the stone are metamorphosed into phyllosilicate minerals. Putting that more simply: after stone is eroded by acid, some of the weathered material (depending on what the stone was made of) is transformed into a material that will become clay – once it attracts the needed aluminum, oxygen, and water.

Clays first forms at the site (in situ) of the stone that is being weathered, and this typically is a form of surface weathering. This new material is a primary clay, and sometimes referred to as a residual clay. These primary clays tend to be grainy, lack smoothness, and do not typically have qualities that are described as plasticity. As primary clays are eroded, (typically by water) and are moved to reform in another location, they are called transported clays.

This transportation changes the clay’s properties; this is likely because the water carries the lighter, smaller gains together, away from the larger, coarser material that remains in the in situ location. When transported clay reforms, the reformation is called flocculation. This natural attraction that clays have toward homogeneous groupings, are due not only to their similar size but because they carry a net negative electrical charge, which the particles gain by adsorption. Adsorption is not to be confused with absorption, is like static-cling. Items are added, or adhered by an electrical charge, to the grains, not absorbed by the grains.

In flocculation, particles are attracted to one another, by their uniform size (typically very small, under 2 micrometers), and shape (tetrahedral and octahedral sheets). These phyllosilicate sheets organize themselves, layering one upon another, like loose pages of sheet music. Between these silicate sheets, aluminum ions and oxygen are sandwiched. These elements bind together to form a clay aggregate, even in the confluence of water. Clay formations can carry with them, varying mineral components such as calcium, titanium, potassium, sodium and iron and other minerals, making them available to the vines. To say that the chemistry of clay gets very complicated, very quickly, is an understatement.

Transported clay has plasticity, which primary clays do not. When a clay is very wet, beyond its liquid limit, (meaning the most water a clay structure can hold before it de-flocculates), the sheets slide apart, giving clay its slippery feeling. Any thick area of clay found at a location is likely to a be transported clay, as the adsorption characteristic of clay allows it to achieve significant mass.

Sand 0.02 – 2.00 mm in diameter
Silt 0.002 – 0.02 mm in diameter
Clay < 0.002 mm in diameterClay types

Francoise Vannier Petit at AlexGamble
Francoise Vannier Petit, inspects the yellow ocher-colored clay in Puligny-Montrachet, Les Grands Champs.  Clays get their pigmentation from various impurities. Brown clays get their color from partially hydrated iron-oxide called Goethite. This yellow ocher clay gets its color from hydrated iron-hydroxide, also known as limonite. Clay type, however, is not determined by its color, but instead by its chemical and material organization.
Different clay types can be found next to each other or layered on top of one another. This layering is called a stacking sequence. photo source: alexgamble.com

The type of clay that is produced from the weathering of rock depends on the what minerals make up the stone.  In the case of granite (the stone which existed in the Burgundy region, before the creation of limestone), is constructed of up to 65% feldspar, and a minimum of 20% quartz, along with some mica. While quartz will not chemically degrade in contact with the carbonic acid carried in rainwater, feldspar and mica will. Even though they originate from the same stone, these two minerals will metamorphose into two different of types clay, that belongs to two different clay family groupings. Feldspar weathers into Kaolinite clay minerals and mica weathers to an Illite clay mineral. These tend to be non-swelling clays. (3)

I probably spent twenty hours trying to figure out what kind of clay eroded from limestone, before I realized that it would depend on what impurities were mixed into the calcium carbonate when it was brewed up during the Jurassic period.  Limestone can produce any of the four families of clay.

Kandites (of which Kaolin(ite) is a subgroup), are the most common clay type, because feldspar, which is the world’s most common mineral, metamorphoses into it.

The other three clay groupings are smectite, illite, and chlorite.(4) Within these clay family groupings, there are 30 subtypes. As might be suggested by the example of the weathering of granite above, it is very common for different kinds clays reside adjacent to, or in layers with other clays. This layering of clay types is called a stacking sequence, and it can occur in either ordered or random sequences. Each are attracted to formations of its own type, by size weight, and electrical charge.

The Effect of  Weathered Limestone on Soil Quality

effect of lime on Clay
effect of lime on Clay

There are a number of significant benefits to the high levels of limestone in the soils of Burgundy. The world over, farmers make soil additions of agricultural lime (which is made from grinding limestone or chalk), in order to balance and strengthen their soils. These are additions that are unnecessary in Burgundy.  Soil salinity is increased by the calcium bicarbonate that is released by chemical weathering of limestone. This increase in soil salinity (which raises the pH) of the soil, is cited as a condition for the flocculation of the clay, allowing the phyllosilicates (clay minerals) to bind together into aggregates. But of course, citing a high ph is required for flocculation (as I have seen written by several authors) this is the chicken or the egg debate. The flocculation requires a low pH environment to occur because it creates that environment in process of its development.

Lime additions to agricultural lands are also beneficial in that it increases soil aeration, which in turn improves water penetration. The calcium loosened soils allow for better root penetration, and because of that root growth is improved. Additionally, agricultural lime strengthens vegetation’s cell walls, increases water and nitrogen intake, and aids in developing enzyme activity. Too much lime (and its accompanying salinity) in the soil, however, can be lethal to the vines, and various rootstock has been identified as being more resistant to the effects of high levels of limestone in the soil than others.

This loosening of soil by addition of lime/calcium carbonate is caused by the disruption of the alignment of the clay particles. Rather than doing a poor job paraphrasing an already excellent article from soilminerals.com, called “Cation Exchange Capacity,” which will I quote below.  To put the article in a frame of reference, it explains to farmers interested in organic and biodynamic farming, the proper mineral balance for healthy soils. These are conditions often exist naturally in the best sections of the slope in the Cote d’Or.

“Because Calcium tends to loosen soil and Magnesium tightens it, in a heavy clay soil you may want 70% or even 80% Calcium and 10% Magnesium; in a loose sandy soil 60% Ca and 20% Mg might be better because it will tighten up the soil and improve water retention. If together they add to 80%, with about 4% Potassium and 1-3% Sodium, that leaves 12-15% of the exchange capacity free for other elements, and an interesting thing happens. 4% or 5% of that CEC will be filled with other bases such as Copper and Zinc, Iron and Manganese, and the remainder will be occupied by exchangeable Hydrogen , H+. The pH of the soil will automatically stabilize at around 6.4 , which is the “perfect soil pH” not only for organic/biological agriculture, but is also the ideal pH of sap in a healthy plant, and the pH of saliva and urine in a healthy human.” soilminerals.com

Mud is the problem, lime is the solution
On construction sites, mud is a problem, and lime is the solution.

The industrial of use of limestone to control wet and unstable soil

The soil strengthening properties of lime is well known by the construction industry. It is used as a soil stabilizer in the construction of buildings and roadways, as well as being used to stabilize wet ground to improve the mobility of trucks and tractors. In the vineyard, soils with high levels of limestone provide the good porosity, soil structure, and drainage to clay soils, and as this construction advertisement depicts, the same for mud/dirt soils as well.

Lime is also the binding agent in cement. The first known use of lime in construction was 4000 BC when it was used for plastering the pyramids, and later the Romans extensively used lime in the preparation of mortar for various constructions. They found that mortars prepared from lime, sand, and water, would harden to a man-made limestone, with exposure to the carbon dioxide provided by the air. This, of course, sounds very familiar, knowing the formation and chemical weathering of stone.


 Next Up Soil Formation: Part 2.2, Soil, Slope and Erosion

NOTES

(1) I should note, that within the span of this short paragraph, carbon has seen several forms: in the air (in carbon dioxide CO2), as an acid (in carbonic acid CO3) carried by water, in stone as calcium carbonate CaCO3, as a mineral bi-product (as calcium bicarbonate Ca(HCO3)2 which exists in liquid solutions. This is all part of the carbon cycle, where carbon is regenerated in the air we breath, the water we drink, the earth we grow our food in.

(2) The fact that CO3 is now carried by water, is important in terms of vineyard development.

(3) Kaolinite clays are the type used in pottery.

(4) As Granite was the primary stone formation in the region prior to the development of limestone, it is likely that Kaolinite and Illites are the most common clay families in Burgundy today.

Marl: The Most Misused and Misunderstood Word in Burgundy Literature?

Mud, Clay, Marl, Silt? photo borrowed from the excellent http://amitiesjerome.com
Mud, Clay, Marl, Silt? photo borrowed from the excellent http://amitiesjerome.com

In trying to understand the effect of ‘terroir’ on the wines of Burgundy, only ‘clay’ has been a keener form of frustration than ‘marl’. But that isn’t because marl is a difficult concept to grasp, but rather because few wine writers seem to really know what marl is. The word is thrown around, even by people regarded as experts, with such seeming abandon, that almost anyone who attempts to understand the word can be hopelessly confused.

Marl is generally defined as a mix of clay and limestone. When they refer to limestone in this fashion, they don’t mean solid stone, they mean that has been mechanically eroded, of varying sizes (from a fine sand to fairly large stones) that are mixed into the soil.  The ratio of these two major elements of marl can be a range of 35% of one, to 65% of the other.(1)  This would be fairly simple, but Wikipedia lists marl as a calcium carbonate-rich mud with varying amounts of clay and silt.

Marl table. With one extreme being all clay and the other being all limestone, marl is a mix of both. Courtesy of wikipedia.
Marl table. With one extreme being all clay and the other being all limestone, marl is a mix of both. Courtesy of Wikipedia

Deep into researching vineyards, I began to realize that much of the information I was reading on soils, (and particularly about marl) was sounding borrowed, shallow and canned. I’ve seen marl written of in myriad ways including that a vineyard had “a mix of limestone and marl” or the vineyard is made up of “Marly clay.”  This one, from one of the more definitive of Burgundy reference books, stated that the soils of Mazis-Chambertin have “a lot of marl mixed in the with the clay and limestone.” But the prize of goes to this gem that spoke of “clayey marly limestone soils”, written by an authority on the subject.

Chardonnay prefers more clayey marly limestone soils from which it can develop sophisticated, elegant aromas in the future wine.”unnamed author

Since we already know that marl is a mix primarily of clay and limestone, you don’t have to think very long and hard to see this statement is contradictory at its core. A soil can be a clay-heavy marl or a limestone-dominate marl, but it can not be a “clayey marly limestone soil.”  All this kind of language does is confuse a difficult subject, and make Burgundy more inaccessible to students of this already arcane subject.

I am not alone in this criticism. On researching marl and clay, I found this article “On marls and marlstones” by geologists Stephen K. Donovan and Ron K. Pickerill that confirmed I wasn’t going completely off base.

“As enthusiastic editors, we cringe whenever we trip over lax use
of terminology and language that authors make, repeatedly, in the
geological literature. We have over 50 years editorial experience
between us and present this note as a brief suggestion for wider
consideration. We have commented on the subject of this paper before
(Pickerill et al., 1998), but, sadly, identifying the disease hasn’t
facilitated the cure, at least so far.”

I could go on and on, and in fact I have. Visit my long 2600 word post: Preface to my upcoming article: “Understanding the Terroir of Burgundy”) for more. Some of the above is excerpted from that post.

________________________________________________________________

(1)  The fact that mud/mudstone (and this is substance is sometimes referred to as shale) is introduced as a term by wikipedia, see table certainly confuses the issue, but they also indicate that this mud is a clay element.

Preface to my upcoming article: “Understanding the Terroir of Burgundy”

(Opinion) and the ensuing quest for answers.

travel-france-pic-liberte
Wine literature champions the one half of one percent of the top vineyards, and the very top producers. What about the wine for the rest of us?

Despite the scores of books written about Burgundy, if you really break down what is being written specifically about each climate, the information can be pretty sparse. For a handful of the greatest vineyards, extraordinary efforts are made to explore the grandness of these few plots.(1)  However, these vineyards probably represent less than one half of one percent of Burgundy. Little coverage is given to the physicality of the rest of Burgundy’s sites, including many highly-regarded premier crus. Beyond listing most vineyard’s size, what the name means in French, sometimes an inane fact (like some wild bush used to grow in that spot) and who the top producers are, most crus don’t seem to warrant the effort. How does Puligny’s Les Combettes differ from Les Champs-Canet, which sits directly above it? It is not likely you find the answer by reading a book about Burgundy.

Of these vineyard entries, writers typically ignore the soil makeup and limestone below; the most primary elements of terroir. Perhaps this is due to a lack of information. (2) However, I have no doubt that if as much effort was given to researching these appellations as is given to tasting Armand Rousseau’s latest barrel samples, we’d have a lot more understanding about Burgundy than we do today. Typically when a comment regarding a particular vineyard’s soil is made by a wine writer, it is simply as a notation, with no connection to the style of wine that comes out of that vineyard. It sits there like a pregnant pause, as though it were quite important, but no explanation follows.  And that explanation is what I hope to supply by my upcoming article. I can’t do what the top wine writers can: go to Burgundy and walk the vineyards with the winemakers, talk to the professors at Lycée Viticole de Beaune. But I wanted these answers for myself; what it all that means the limestone and “marl” and clay, and what did for the wine. If I could. Did I dare?

While I am critical of the much of the wine writing produced – for its lack of deeper educational and intellectual content, I understand that wine writers must produce what consumers are willing to pay for. We are a consumer-driven society, and readers are really looking for buying guides wrapped up in a little bow of information. The capitals of 19th century Europe were famed for their starving intelligentsia, but no one wants to scrape-by in a land of plenty, regardless of how romantic. Wine writers write what the public wants.

The beginning

Way Too Geeky!
Way Too Geeky!

After more than a year of researching Burgundy vineyard information for the marketing part of my job, I thought I could do a quick write-up about the terroir of Burgundy. I had come to some interesting conclusions and felt I could write a piece with a unique perspective on vineyard orientation, slope, the general soil types determined by that, and how it all relates to a wine style.

It was all going along quickly and easily until I wanted to clarify a couple of points about geology. What had initially looked like a weekend project, has taken 9 months of daily work. This article has become something of a Leviathan, but the exploration has taken me to uncover some enlightening information, as the pieces started falling into place. The original piece first became two parts, and ironically, now it is four parts, each divided into articles of a more manageable size of 2,000 to 4,000 words. The result of this is untold hours of research and writing.

Unfortunately, sections of Part One have ended up being so technical that I no longer really know who will want to read it. Any hope of an audience is slim. Most wine professionals are so burnt by the end of the week, that they would rather paint their house than read about wine. However, this is a unique article that looks at the breadth of the factors that influence vine growth in Burgundy and ultimately influence wine character.

An example of a map showing the vineyards I'm highlighting, as well as the soil and limestone base it sits upon.
An example of a map I developed, showing the vineyards I’m highlighting, as well as the soil and limestone base it sits upon.

A Path of Discovery and Frustration

One of the first surprises was difficulty justifying the satellite images with some of the vineyard maps that I had been so diligently studying. Sometimes they just didn’t look like the same place. The vineyard maps often gave little sense of topography of the hillsides, despite paying particular attention to the elevation lines. I believe that the amount of slope in vineyards that are not terraced, like in Burgundy, is critically important to the profile of a wine.

What looked like roads on a map, at times were not, and in many places, there were entire sections which were shown as vineyard were actually unplanted, inhabited only by trees, scrub or rock. This I found to be very illuminating information regarding adjacent vineyard land, and how that might define a wine’s character. At times, the shapes and sizes of vineyards depicted on maps appeared to be different from the photos, perhaps changed to fit the artist’s needs.  After a while, I started making my own maps using Google Maps’ satellite images and adding the information that I found relevant to the needs of my job. Perhaps the most telling visual information has come by utilizing Google Maps’ street view, to see a vineyard and its slope, the topsoil, quickly and easily, and often from multiple angles. It is an amazing tool, I highly recommend using it in addition to maps when studying wine regions.

Am I a Skeptic or Just Paranoid?

Marl table. With one extreme being all clay and the other being all limestone, marl is a mix of both. Courtesy of wikipedia.
Marl table. With one extreme being all clay/mud and the other being all limestone, marl is a mix of both. Courtesy of wikipedia.

I noticed that the information I was reading, from multiple sources, wine writers, importers, etc, was all starting to seem repetitive, using similar wording, ideas, phrasing. Increasingly, the information seemed more and more borrowed, shallow and canned. For instance, it is common for a writer to state that a vineyard is “a mix of limestone and marl” or the vineyard is made up of “marly clay.” And then there was this from one of the definitive Burgundy reference books regarding the soils of Mazy-Chambertin: “there is a lot of marl mixed in the with the clay and limestone.”

Marl is generally defined as a mix of clay and limestone. When they refer to limestone in this fashion, they don’t mean solid stone, they mean rock that has been mechanically eroded, of varying sizes (from a fine sand to fairly large stones) that are mixed into the soil.  The ratio of these two major elements of marl can be a range of 35% of one, to 65% of the other. (3) The more I read, the more I question what I am reading. (4)

Below is an example kind of “soil information” that I’m talking about. At first blush, the passage below sounded like I’d found the holy grail of explaining what kind of soils for which Pinot and Chardonnay were best suited, but later I realized it was anything but.  The following was written by an authority on the subject.

_____________________________________________________________________

“• Pinot Noir flourishes on marl soils that are more yielding and porous, that tend towards limestone and which offer good drainage. It will produce light and sophisticated or powerful and full-bodied wines, depending on the proportion of limestone, stone content, and clay on the plot where it grows.”
“• Chardonnay prefers more clayey marly limestone soils from which it can develop sophisticated, elegant aromas in the future wine. The clay helps produce breadth in the mouth, characteristic of the
Bourgogne region’s great white wines.”

______________________________________________________________________

With the Pinot, he starts off well. Marl (a combination of clay and limestone in varying percentages) with very high levels of calcium carbonate (limestone) is has a correspondingly high-rate of infiltration by rainwater. And he is right again as he writes that the weight of the wine is dictated by the “proportion of limestone, stone content, and clay on the plot where it grows.” 

The problem occurs when he tries to differentiate the conditions in which Chardonnay thrives. “Chardonnay,” he writes, “prefers more clayey marly limestone soils from which it can develop sophisticated, elegant aromas in the future wine.” If we compare the soils and bedrocks of the finest Pinot and Chardonnay vineyards, there are tremendous commonalities, and both varietals seem to flourish on the same soils. Every aspect of what he said about Pinot equally applies to Chardonnay.  Second, as marls increase in their clay content (which is what he was trying to say with the utterly confusing description of “clayey marly limestone soils“), these denser soils, which typically occur at the curb of the slope, are still capable of excellent drainage. We will look at this in depth later, but for an immediate explanation see below (6),

 

To make this passage more accurate, he should have led with drainage. The porosity of the soil allows drainage: in other words, it has a causal effect of good drainage. It is not an axillary attribute as he suggests when he writes “and which offer good drainage.”

Secondly, it seems that the writer is suggesting that Chardonnay does not do as well as Pinot Noir in porous limestone dominated soils, and vice-versa. I believe vineyards like Les Perrières in Meursault, that have very poor, and very porous, limestone soils, with little clay content, contradicts that notion. Additionally, in Chassagne Montrachet, Chardonnay has replaced much of the  Pinot Noir on the upper slopes of the appellation, while Pinot Noir has remained in the heavier, clay-infused soils lower on the slope.

“Now every piece of information had to pass the smell test, and preferably it needed to be corroborated by another source, that clearly wasn’t of the same origin.”

Skeptic: everything must pass the smell test.
Skeptical, now everything must pass the smell test.

I plodded on with my inquiry. Now every piece of information had to pass the smell test, and preferably it needed to be corroborated by another source, that clearly wasn’t of the same origin. I had read enough to identify “family trees” of bad information, and I often believed that I could often identify the original source.  Just how easy it is to pass on incorrect information is illustrated by this next example. I found an error (in my opinion) in one Master of Wine’s book on Burgundy, saying that the “white marl” of a vineyard was found on the upper slope, producing a richer, fuller wine, and while the calcareous (limestone) soils were down below, and produced a lighter wine. It was an obvious mistake if you just thought about it for a second, as the forces of gravity and subsequent erosion drive clay to the lower-slopes where it reforms via flocculation. Later I would find the same information, but in more detail, in another Master of Wine’s article, again containing the same error.(6)  The source of the error was either a mistranslation of a conversation with a vigneron or a typo. While this is a simple mistake, having two of our most revered Master of Wines citing the same information can only confuse an already misunderstood subject, even further. I can envision a whole generation of Sommeliers reciting that the upper-slope of Les Caillerets produces heavier, more powerful wine than sections of Caillerets farther down the slope.

It was clear I wasn’t going to find the answers I was looking for in the English language Burgundy books I had access to. Ultimately my questions would become more and more specific, pushing my inquiry of terroir to an elemental level – delving into the construction of the earth and stone, and how it breaks down, and how it might influence the wine we ultimately drink. I still have a tremendous number of questions that will simply go unanswered for quite some time,(7) either due to the lack of research, or that this information is not available in an accessible, English-language format.(8) 

Part One of the article is the result of searching out, reading, and trying to understand small, maybe inconsequential details.  Since I’m putting it out there on the internet, I have made a concerted effort to attempt to get it right. Obviously not a geologist, so despite reading about clay and clay formation dozens of times, from dozens of sources, the complexity of the science makes it easy to over-simplify, to misunderstand it, and definitely, easy to misrepresent. Making this process more difficult, I could find no articles that (for instance) were specific to the clay and clay formations of Burgundy. (9)

It’s not sexy reading, but I’ve done my best to pull it all together into one place.  If nothing else, I hope this can be a jumping off point for others to research, and expand our cumulative understanding of terroir. 

 

 

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ADDITIONAL NOTES

(1) Even with the top vineyards, publications heavily link the greatness of the wine to the producer, rather than the vineyard. The mantra for the past 30 years has been: producer, producer, producer. While there is a historical reason for this producer-driven focus, I feel the vast improvements in viticulture and winemaking knowledge over the past two decades, coupled with the concurrent global warming, has changed the paradigm and significantly leveled the playing field between producers. There are now much smaller differentials in quality from the top producers and the lower level producers. I feel that the focus should now return to the vineyards of Burgundy, each with a distinct set of characteristics due to its orientation, slope, and soils. Nowhere else in the world is this kind of classification so rigorously defined. And because of that, nowhere else in the world is this kind of ‘study’ possible.

(2) The mapping of Limestone has never really been done before the geologist Francoise Vannier-Petit began her work a number of years ago. She has now mapped Pommard, Gevrey, Marsannay, and Maranges, for the trade associations that have been willing to pay for her services.

(3)  The fact that mud/mudstone (and this is substance is sometimes referred to as shale) is introduced as a term by Wikipedia, see table certainly confuses the issue, but they also indicate that this mud is a clay element.

(4) To give credit where credit is due: When I first started doing an overview of our producers, I had summarized this idea, (Pinot liked preferred limestone soils and Chardonnay preferred more clay-rich soils.) My boss, Dr. George Derbalian (with his background in failure analysis) looked at the statement and said, “I don’t know about that.” He asked where I had obtained this information, and when I couldn’t immediately produce the source, he warned: “You have to be very, very, careful about these things. As an importer, we have to be completely sure we are right when we say something. I would like to remove this sentence.” I thought he was being over-reactive at the time, and 100% accuracy wasn’t important for the marketing piece I was working on, but later, with much more research under my belt, I would revisit his words with far more respect.

(5) The word marl has a very poorly defined meaning because it is a very old word that was used somewhat indiscriminately. Wikipedia lists marl as a calcium carbonate-rich mud with varying amounts of clay and silt in their of the definition. To make matters more confusing Wikipedia’s definition of mud says it has clay in it. Is mud part of marl? Is clay part of mud? Does it really matter?

6) This is for two reasons: first, because of the shards limestone, in the soil, weathering of that material by rainwater produces an abundance of freed calcium. This is sometimes referred to as “active” limestone. This calcium, which is mixed by plowing with the clay, misaligns the platelets in clay causing the clay to lose its plasticity. This misalignment greatly increases the infiltration rate (IR) of water through the clay. So while clay alone has very poor IR’s, clay that has been mixed with calcium has much-improved drainage. The second reason that these richer marls, meaning an equal or higher percentage of clay than limestone in the mix, produces richer wines is there is more root space in the vineyards which our author is writing about, (ie le Montrachet and Batard-Montrachet). This occurs because of the location in which clay increases in the soil, happens in places where the slope is leveling off. These locations are where gravity has sent the hills colluvium. Here is where the hillside’s scree, sliding down, due to erosion or from man’s working the land, sits, and upon it, water runoff and gravity have sent the clay, eroded from the hillside above, to this same spot. This convergence of higher proportion of clay in the topsoil and limestone colluvium, together, provide a deep, rich soil that has excellent drainage for the level of slope. Of course, we will get into the science of this in much greater detail, later.

(7) The quote from the second Master of Wine’s write up of Les Cailleret. I have added the (er) to here to make the passage more clear. “Up at the top of the slope, there are outcrops of bare rock. He(re) we find mainly a white marl. This will give the wine weight. Lower down there is more surface soil and it is calcareous, producing a wine of steely elegance. A blend of the two, everyone says, makes the best wine.”

(8) The list of questions I have that don’t have answers seems limitless.  Here are my top questions with no answers at the present: 1) How pervasive is is the fracturing of limestone in the top crus, 2) what kind of limestone is it?  3) does the limestone there to fracture and is thus friable? 4) how much water do these limestones hold?  5) how much groundwater is available to the vines? 6) How does the groundwater circulate, and 7) how quickly through different types of soil?  8) Where are the faults in the various top climates, 8) are the faults often at the boundaries dividing limestone types? 9)  how deep are the drop-offs (covered by the topsoil) created by the various faultlines?

(9) The University, Lycée Viticole de Beaune is likely to be active in this kind of research, but so far I have not been able to access what might be available, and correct translation from French to English can be problematic if it isn’t done by the author who wrote it, and many times more so if using a translating program (software).

(10) Therefore I’m unable to discuss the types of primary clays, called kaolins which may have formed there, in situ, instead focusing on transported clay that has been derived from the erosion of limestone of the vineyards, called Chlorites.