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jsbt_gw

Clay soil burning

jsbt
10 years ago

Hello :-)

I have a small piece of land. A small 4 meter x 4 meter part of it is of the best clay soil, perhaps the best in the world for making pottery: hard as a rock when dry and like chewing gum when wet. When dry that soil laughs at my pickaxe and when wet it glues my pickaxe to the soil. Not even grass can grow there. However, I am not interested in pottery industry, but growing my plants there.

I read a lot about clay soils and about composting them. Recently I found an article in an very old magazine here http://chestofbooks.com/gardening-horticulture/Journal-2/How-To-Improve-Stiff-Clay-Soils.html#.UmUDnvnxrZ . At the end of the article, it mentions that there is an explanation on how to burn clay: "For the process of burning clay, see Horticultural vol. ii. p. 442, and vol. iii. p. 184. Ed."

However I cannot find the mentioned article on clay burning. Seems like when clay is burnt it will become a bit more porous and will not aggregate any more. This would facilitate draining and also adding compost to it. However, there should be the cons which perhaps were not taken into consideration 130 years ago: burning the clay would perhaps destroy nutrients? And if I burn clay and then add compost to 'refill' nutrients into the burnt clay? It would be bad if from clay that piece of soil becomes as sandy as the Sahara.

I made research, contacted the owner of the website that hosts the above book, nobody knows about clay burning. It seems clay burning is kind of a subject lost in history. I never found anything on that and there is no explanation on how to do it. As my piece of land is small, I would be willing to try clay burning and adding compost, provided it will not destroy the soil.

All your ideas, suggestions and information on the clay burning subject are welcome.

Comments (30)

  • Kimmsr
    10 years ago

    Clay soil particles are inert minerals and by themselves would not support combustion, something that would support combustion would need to be added to that soil and then enough to create sufficient heat to cause the soil particles to expand. It would be far easier to do that in your oven, but then that would stink up the house for a fairly long time.
    Heating that soil to a temperature that might cause the clay particles to expand would kill off any part of the Soil Food Web that might be there.
    The link you provided did not work, hopefully this one will, but it does not really address the question of how to "burn clay soils".
    Make your life much easier and simply add enough organic matter to that soil.

    Here is a link that might be useful: 1851 advice about clay soils

  • seysonn
    10 years ago

    It is interesting:
    Isn't that how bricks are made from red clay by firing ?
    Now, instead of forming the clay into a shape, make it into smaller pieces or even particle and fire. Those small particle would be like if you crush a brick or a clay pot. They will not stick togetther anymore and will have porosity to retain moisture.
    In effect that is how things like Turface and Floor-Dri are made.

    But I suppose it might not be economical to do it in a large scale due to high energy costs.

  • jsbt
    Original Author
    10 years ago

    Hello Kimmsr, thank you for the link, this is exactly the article mentioned in my opening post. You are right,composting will work in the long run. However, I found very interesting this old technique from 1851, which is forgotten now, perhaps because as Seysonn explains, it is not economical. In my case, I am cleaning my piece of land, I have plenty of old wood good for nothing except to burn. As the clay soil is restricted to a small 4x4meter area, I would like to try the clay burning process and then post the results here. But first, I need to find how to do it. Back in 1851, perhaps farmers just cut down trees to open a new area for cultivation and burned the logs there in place? Please, share your thoughts and ideas.

  • toxcrusadr
    10 years ago

    I have not heard of this as a soil treatment but it makes a certain amount of sense. I suppose they may have just built a fire over it, but it would likely only heat the first few inches to a very high temp.

    It's not so much burning of the soil itself, but more like kilning. To do it efficiently, it seems to me you would need to find a way to make sure the clay is broken up while being heated. Otherwise you end up with enormous clumps like bricks which then have to be broken up. They do have million-dollar machines that can heat soil while tumbling it down a rotating drum - similar to a cement kiln. I've seen these in action. Not feasible for a home garden.

    What I would do, is build a raised bed with imported soil over top of this stuff. It sounds so bad that you'll be there for years trying to fix it. And this is coming from someone who has spent years fixing clay soil, so I'm not a wuss in this department.

  • jsbt
    Original Author
    10 years ago

    I will never fully understand how Google algorythms work. I spent a couple of weeks looking for the Horticulturist books online and never found anything. Now, in a couple of clicks, I found volume II. And there is how to burn clay soil. They say it is easy and I believe so, for small volumes, and resolves quickly the issue. I will do it next February or March and post here the results. Here you have the text, which has no copyright:
    ******
    * A simple mode of burning: clay in the kitchen garden is the following: make a circle eight or ten feet in diameter, by raising a wall of sods a couple of feet high. Place a few large sticks loosely crosswise in the bottom, and upon those pile faggots or brush, and set fire to the whole. As soon as it is well lighted, commence throwing on lumps of clay, putting on as much at a time as may be without quite smothering the fire. As soon as the fire breaks through a little, add more brush, and then cover with more clay, till the heap is raised as high as it can be conveniently managed. After lying till the whole is cold, or nearly so, the heap should be broken down and any remaining lumps pulverised, and the whole spread over the surface and well dug in ' As an example." says Loudon, " of the strong clayey soil of a garden having been improved by burning, we may refer to that of Willersly Castle, near Mattock, which the gardener there, Mr. Stafford, has rendered equal in friability and fertility to any garden soil in the country. "When I first came to this place,' says Mr. Stafford, "the garden was. for the most part, a strong clay, and that within nine inches of the surface; even the most common article would not live on it; no weather appeared to suit it; at one time being covered by water; at another time rendered impenetrable by being too dry. Having previously witnessed the good effects of burning clods, I commenced the process, and produced, in a few days, a composition three feet deep, and equal, if not superior, to any soil in the country.' "
    *****

    Hope to have helped gardeners with the same issue as me.

  • avgusta_gw
    10 years ago

    I would not say it is easy or makes any sense .

    If you are able to dig out a clump of clay to throw it in the fire, it means you are able to shovel the whole area and amend it with organic matter and solve your problem with heavy clay.

  • Hammerga
    10 years ago

    I agree with avgusta. My garden is 100 feet by 125 feet of red Georgia clay. I have added sandy soil and compost and it does well. I do raised rows a no till method and if I turn it at all I turn it with a fork and never walk on my rows also.

  • ericwi
    10 years ago

    Pure clay will not burn, but it will absorb a lot of heat before it is completely dried out. I am sure that there are locales with "clay soil" that contains significant organic material, and that stuff will support combustion. Our local soil, here in Madison, is fairly high in clay, but also has considerable organic component. I am able to dig up and break up the clay clods, and work in compost made mostly from leaves. Our garden soil is now easily workable, but it took several years, and many annual additions of compost, to achieve this.

  • nc_crn
    10 years ago

    That whole book (actually a collection of articles) is a trip.

    I've never heard of "clay burning" myself, but it seems to be a way to harden off small aggregates of clay improving air movement in the soil and lessening water holding capacity in the clay.

    Basically, when clay is cooked to a high enough temperature (especially those high in iron/iron oxides and aluminum/aluminum oxides)...the clay can harden up and become dehydrated (more accurately, de-hydroxylated (removal of OH- groups attached to the clay)). This makes parts of the clay hydrophobic (water repelling) which keeps it from getting "sticky" and improving air movement through the soil. It's not permanent, but it can be rather long lasting (years/decades).

    That said, this is a very difficult and overkill way to go about improving soil. It might be best to leave this one in the 1850s.

    This post was edited by nc-crn on Tue, Nov 26, 13 at 20:14

  • toxcrusadr
    10 years ago

    OTOH, if no one here has actually tried it, how do we really know?

    From the description, the author made a 3-ft thick deposit of clay and biochar. I gotta wonder how much of the improvement was also due to the charcoal.

    I have a rural property with some terrible clay, some of which is in piles as we speak, and I also have brush piles in need of burning. Hmm.

  • jsbt
    Original Author
    10 years ago

    @nc-cm, thank you for the explanation, very interesting. @hammerga, compost is sure a solution and will solve the clay issue as you say after some years of work. I was reading another page of the book and the author says exactly that, compost will work in the long run, clay burning is an instant solution. I was worried clay burning would destroy the soil, but the author says the contrary, as it faciliates penetration of compost and organic matter. @toxcrusadr charcoal may play a part, but as nc-cm says, clay burning causes a chemical reaction removing OH. I will burn the clay on March, if you also do so, please post here the results. On my case, I will not build a a wall, but burn the layers of clay and brush inside the same hole in the ground I retired them. I am glad to have revived this long forgotten solution. Let's see if it effectively works! :-)

  • Kimmsr
    10 years ago

    Putting any pollution concerns aside this most likely was not a too popular thing to do because in reality it did not do what was expected. Since the kilns that the now extruded and dried clay is placed to fire into bricks need to be in the 900 to 1200 degree range I doubt that burning in the filed would produce anything similar.
    Adding organic matter to clays is much easier then would be trying to prepare that same clay for burning, I would think.

  • wayne_5 zone 6a Central Indiana
    9 years ago

    Thank you jsbt for reporting back. I have to wonder how long the change would last out there in the open garden.

    I like the idea of changing the texture and structure by adding large amounts of sand and peat moss and lots of other organic matter to clayey soil. It works nicely for me.

  • Kimmsr
    9 years ago

    Keep in mind too that some things people believed in the 1850's today we know is nonsense.

  • jsbt
    Original Author
    9 years ago

    The good thing is that we should never stop learning and checking things. The original article in 1851 was written at the Horticulturist because of a demand from a reader: "that articles which may be obtained of the dry salters are much more accessible to me than wood ashes, peat, etc, which every farmer in the country can easily obtain, but which are less abundant here than guano. Very respect-fully yours, E. R. Boston, April 28,1851." His problem was that peat moss and other organic matter was difficult to obtain. The articulist then made reference to an alternative process, clay burning - and he mentioned the name of the person and the city where that person worked during some years burning clay in his backyard and obtained a very good soil for legumes, the articulist say. It was then a bit more than a mere belief, it was tested by someone before. And according to my test, it works, therefore it is not nonsense - if you do not have other solutions at hand. In my case it is easier to purchase compost. I did it once in in the lower half of my piece of land and incorporated 4 tons of compost using a rented tractor, it worked very well as wayne_5 says and after 3 years I still see how the compost ingrained itself into the clay soil and the earthworms doing their job very well - I am amazed how they manage to dig their tunnels into that sticky soil, sticky enough to stop pickaxe like glue. But this clay burning works too, only it is much more time/energy consuming. But tell you what: I will burn more clay and make a special bed and plant some vegetables there, just for fun and to test how they will grow on this burned clay soil.

    This post was edited by jsbt on Tue, Apr 15, 14 at 8:33

  • toxcrusadr
    9 years ago

    I would like to see some pics of how this works. I don't quite see how wood can burn when down in a hole layered with soil. How does it get enough air? Or are you only placing a few chunks of clay amongst the sticks and branches?

  • Slimy_Okra
    9 years ago

    Something else to keep in mind is that burning will drive off organic acids and cause a large increase in soil pH.

  • wayne_5 zone 6a Central Indiana
    9 years ago

    Again, how long does the result last?

  • jsbt
    Original Author
    9 years ago

    @toxcrusadr: at the present stage of the soil, as sticky as it is, I did not manage to grind it into small pieces but only take chunks with a pickaxe, there was plenty of free space for air to come in. The burning pine tree branches also provided space for air.
    @wayne_5: it depends if clay burning leads to a physical or chemical reaction. A physical reaction could be reverted. A chemical reaction mostly not, afaik (I can be wrong). I believe it happened a chemical reaction, as the soil colour changed from light tan into reddish or rust depending on the chunk of soil and when I dissolved it in water it turned into a chocolate colour. Here you have a picture http://s23.postimg.org/tprwib3jv/DSC_0070_1.jpg of a small quantity of burnt clay I mixed with water. The big difference is that it dissolved in water while the non-burnt clay soil is sticky like epoxy and hardly dissolves in water. Notice the colour: not tan anymore, but chocolate. When dry is reddish colour like those commercial bricks sold everywhere. If this clay burning was a chemical reaction as perhaps nc_crn explained better above, then it will last a long time (perhaps forever).
    @slimy_okra: yes you are right, whatever little organic matter in that "epoxy-like" soil, it was burnt. The minerals are there though, even after burning.
    ===
    PS:Clay burning is very time consuming, but I am thinking just out of curiosity to burn more clay and try to setup a small test bed for legumes and see what happens. If and-or when I do that I will post here the results with pictures.

  • toxcrusadr
    9 years ago

    "Organic acids" is probably not the most correct term here. Carbonates (calcium and magnesium, mostly) decompose to give off CO2, and when they are rehydrated, they form hydroxides which are very alkaline. This is why ash is alkaline anyway, and I suspect ash will control the final pH if it is mixed into the soil, at least temporarily until it's leached out. I had not thought about what happens to the clay though. Depending on the type of clay it may go through a similar process. I would think, although don't have specific knowledge, that the clay would recover also after it's exposed to the environment. Did the original book discuss this?

  • wayne_5 zone 6a Central Indiana
    9 years ago

    I saw part of a soil health video where chunks of soil were dropped into water. Unlike what you would think, it was the ones that did not melt down quickly that were considered of better structure. I don't remember the why, but might guess that too fine of melting and merging for clay loam soils might let them recongeal into hard lumps when they dry. Now if the texture is coarse enough, that would not be a problem.

    Deflocculated soils make hard lumps. Sodium and magnesium deflocculte, but calcium flocculates soil and makes soft and fluffy lumps.

    This post was edited by wayne_5 on Wed, Apr 16, 14 at 15:26

  • Paul Hadfield
    8 years ago

    Merriam Webster dictionary says "the burning or roasting of clay especially in Great Britain for use in improving the soil".

    Sure enough, I reached this discussion group by seeing reference to 'burning clay soil' on the CURRENT UK government website, in relation to my investigation of agricultural tenancies here in little old England. It says (at https://www.gov.uk/agricultural-tenancies) that in relation to compensation to a tenant at the end of a tenancy :

    "The
    tenant is entitled to compensation for the following : ...... Short-term
    improvements, including:

    - protecting
    fruit trees against animals

    - clay
    burning

    - liming
    and chalking of land"

    So clay burning must have been done on quite a wide scale - by burning brushwood on top of the soil I guess, rather than by attempting to dig it all up and throw it onto a fire.

    Weather permitting we will be driving past Willersley Castle in ten days time (near Matlock in the Peak district here), and will see if I can persuade my family they might fancy calling in for a spot of tea, eh what?, in the hotel which now occupies it.

    If so I will see if I can quiz the gardener about clay burning, and wonder if we will find the venerable Mr. Stafford still in residence 165 years on, and still enthusing about his garden soil - his ghost must surely still haunt the place at the very least. The tea room might even offer produce from that very garden, in which case I will report back on its quality.

  • toxcrusadr
    8 years ago

    Greetings from the Colonies and welcome. We anxiously await your findings.

  • idaho_gardener
    8 years ago

    This is awesome! We have a lot of gardenweb cousins in the south who will probably benefit from this technique. I would have loved to try this when I lived in Idaho, but adding humic acid rendered that good clay soil into a friable topsoil. Tox, I'm going to be curious to hear how well it works for you. These days I'm living in the land of silt, and clay soil is a luxury that I miss.

  • davidzcrookes
    8 years ago

    Sorry to arrive late. The locus classicus here is Montagu Allwood, Carnations, Pinks and All Dianthus, page 72 ff. I'll type out the pertinent passage, but everyone should try to acquire a copy of Allwood's wonderful book.

    BALLAST
    OR BURNT EARTH

    The great value of this consists not only
    in the potash it contains, also its special help in lightening and giving
    drainage to heavy soil, but in the wonderfully stimulating effect it has upon
    root action, especially with all members of the dianthus family. It supplies something which is beyond the
    reach of the chemist.

    To make ballast it is a good plan to dig
    out some of the stiff, dense subsoil and burn it in small fires, conveniently
    distributed. A number of small fires are
    better than one big one for making burnt earth, because if the clay is lightly
    burnt it loses its tenacity and then a small amount of plant food is made
    available.

    To make ballast as hard as brick dust a
    large fire is necessary because that generates more heat.

    We at Wivelsfield burn clay for all our
    carnations and dianthus, using about one-eighth in the compost, but as much as
    one-quarter in soil for sowing dianthus seed, and also for early pottings. Undoubtedly the potash so supplied is in a
    form which is most beneficial and health-giving.

    We dig stiff yellow clay and burn this when
    wet during the dull wet months of the year.
    In fact it is difficult to persuade it to burn freely when it is
    dry. We commence with a large fire of
    wood, and when this is partially burnt, we cover it with the wet clay sprinkled
    with a little soft coal dust. This is
    the only secret. If the clay is too soft
    and wet, or too powdery and not in lumps or clods which admit air or draught,
    or if the wind causes one side to go dead, then iron pipes are placed to
    encourage a draught. The ballast heaps
    are kept smouldering for months. As the
    clamp burns through, usually twice in the twenty-four hours, it is covered in
    with clay and a dusting of soft coal dust.
    In fact, it must be kept well covered so as to preserve the heat, yet
    not smothered. When the heaps get too
    high they are dragged down with iron drags, a portion at a time, and covered
    with clay and coal.

    The ashes or ballast are sieved before
    being used and we prefer to keep them dry.
    The lumps are allowed to weather.
    Pure wood ashes of course contain more potash but are not so beneficial
    to heavy soils, because they do not keep them so well aerated.

    Some will ask, is all this expense worth
    while for growing carnations? To grow
    the best it is always worth while.

    Our father, when a farmer on the wolds of
    Lincolnshire, always sowed sieved burnt earth with his turnip seed, and he was
    famous locally for his exceptionally fine crops. He used to plough up the turf on the sides of
    the parish roads (you could take liberties like that in those days) and burn
    these turves when dry during the summer time.
    The method employed was to make a circular well of turves with spaces
    for draught around a large heap of wood, fire the wood and, when nearly burnt
    through, put turves upon the embers, then close the whole lot in with turves as
    it burnt through. This sod clamp would
    burn for weeks. Undoubtedly the roots
    and humus in the turves, and also the draught, must have assisted the burning,
    because I well remember in those now distant years that everything seemed to be
    consumed. However, for turnips the old
    Governor never used the ashes for at least one year. They were then sieved and sown with the
    turnip seed through the drill. When the
    wolds in Lincolnshire
    were reclaimed from being merely rabbit waste land much of the surface soil was
    burnt in long ridges on the hills. That
    would be, I imagine, during the Napoleonic Wars.

  • HU-665503972
    5 years ago
    last modified: 5 years ago

    I have a great interest in old bricks and I recently came across a newspaper article from 1727 which refers to clay burning and thus I thought it may be of some interest to you - " The lands of Gogar, lying in the shire of Clackmannan and the Parish of Alloa (Scotland) are designated to be sold by a voluntary roup in the months of May or June next. There is a well contrived house........to the extent of 277 acres.......and the whole may be so at a very easy expense, there being one of the best free stone quarries in all the County, on the East part, which wants chiefly to be brought in. There is clay to be had in several places where of good brick has already been made, and the clay at hand to be burnt for manure. The ground is almost surrounded with coal works, within less than half a mile or a mile of it........ " www.scottishbrickhistory.co.uk

  • Paul Hadfield
    5 years ago

    I did call in very briefly at Willersley Castle in July 2014, but unfortunately the walled garden has been sold off by the hotel and Mr Stafford was not to be found. Time didn't permit me that day to attempt to find where the garden had been.


    If I had looked in advance at the satellite picture on Google Maps at https://www.google.com/maps/@53.1138952,-1.5569823,159m/data=!3m1!1e3 I would probably have seen that there is a walled garden area a hundred yards to the north of the castle, which is now apparently someone's lawn, and is probably the area in question. Mr Stafford must be turning in his grave as all his soil improvement is reduced to lawn. Now that I have seen where it is, I shall call in if I have time when next passing, and knock on the adjacent owners' door. But being under grass it may be that they know nothing of the quality of the soil below. After 150 years the beneficial effect of the burning may be somewhat reduced anyway. Shame. Interesting to hear about the lands of Gogar however, having lived in nearby Glendevon for 6 months over the winter of 1982-3, although I never attended a roup there, voluntary or otherwise.


    Anyway we are on heavy clay here in south Leicestershire and have been using well-matured sheep manure from a local farm to supplement our own garden compost, and have had very good results. Once the organic matter content is raised, the clay is the most fertile soil there is, with huge nutrient content compared to sand or even many silts. It is difficult to produce enough organic matter to significantly raise the organic matter content on an agricultural scale, but easy enough in the average garden.


    A fascinating thread all round, and thanks to all for the information.

  • armoured
    5 years ago

    An interesting thread and I have to admit I was very skeptical - but after reading a bit I think the positive benefits for a garden plot are probably rather straightforward. (I'd still not use it because of air pollution and waste of burning like this).

    This is speculation of course. But I think the benefits are mostly due to air/oxygen penetration, improved drainage, some charcoal/biochar addition plus some remaining organic material.

    Thinking it through, what do you get when you burn woody materials in oxygen poor environments (i.e. by tossing lumps of clay and partly smothering)? Charcoal - as well as some left over woody materials (inside some of the charcoal lumps). That's going to leave charcoal to absorb and release air and water (as well as other benefits).

    The heat will drive out some/all moisture from the clay, causing some expansion of the clay and cracking some of the clay structure, possibly making some of the clay hydrophobic, but not entirely so. If the heat is not too high/fast and the clay damp, it would avoid baking them into bricks (if the clay is not dry, water expanding would contribute to this cracking - I believe bricks are made from dried clay).

    These effects would address some of the main issues with a heavy dense clay - lack of air due to density and poor drainage.

    So I can see why this would work, particularly if then mulched with compost or manure or whatever (providing an environment for worms and others) and then planting with a good rooting plant. Some other impacts would be similar to what farmers would get from clearing land of forest by burning (potash and the like, although not clear to me clay soil is deficient of these).

    That said, bad air pollution impacts (smoke from incomplete low temperature burning is pretty noxious), as well as wasteful. So I personally wouldn't want to try it out.

  • Chris Resnicke
    last year

    "Pit firing" is an ancient method of making low-fired pottery like terra cotta. Low fired clay is not vulnerable to water, but is porous enough to allow water to evaporate & even seep through it. The process is quite similar to what's described above: you dig a pit, put a layer of fuel (like wood chips), put your pottery in, put more fuel on, then build a big fire on top of that. Keep adding fuel to the fire until you have a bed of hot coals that totally covers your pots, then spread a layer of pottery shards over the top to insulate it. The whole setup is the original primitive kiln & reaches temperatures *far* beyond what you get from a regular campfire.


    If you do what is described in the previous comments (dig a hole, build a fire, then alternate between layers of fuel and clay) then it is definitely plausible that you could fire the soil enough to turn at least some of those clods into low-fired clay. That is very similar to soil amendments used even today like hydroton or expanded shale.


    Additionally, it is interesting that one of the quotes calls the addition of a bit of powdered soft coal the secret to making this all work. In Europe, "soft coal" refers to some types of coal that coincidentally have a relatively high sulfur content & a relatively low energy content. The small amount of coal described here would do nothing noticeable to the heat, but the chemistry here seems to lend credence to the idea that this would improve results.


    When wood burns in a very hot fire, the ashes left behind are primarily composed of Calcium Oxide (lime), which is very basic and Calcium Carbonate, which is neutral but will dissolve in acids & neutralize them. Rainwater has always tended to be a bit acidic because of dissolved CO2, so when that calcium oxide gets into solution with rainwater it will react to also form calcium carbonate. When the soft coal burns in a pit & gets buried, most of the sulfur in the coal would be trapped in there as well.


    As various soil organisms repopulated this area, they would eventually turn that soil sulfur into sulfuric acid. Sulfuric acid + calcium carbonate = calcium sulfate, aka *gypsum*, which is also commonly used today to loosen clay soils. So what we end up seeing here is that the wood ashes mixed with the coal ashes in the presence of a healthy soil ecosystem would end up acting like a slow release fertilizer & soil amendment, while the burned chunks of clay increase soil permeability & prevent the soil from ever reverting to the original structure. The amount of calcium carbonate formed here is likely to be very significant, so it would probably continue to buffer against soil acidity for a very long time.


    If that area then regularly received compost & manure, that additional sulfur would probably help maintain the effect (not to mention the sulfur inevitably contained in the rain if this was anywhere downwind of an English city burning coal to keep warm). Plus, this method kills off everything that was in the soil. Not ideal, but it would kill off any pests & new compost would reintroduce beneficial microbes, so the new soil ecosystem would likely recover quickly & be much better for crops. Any leftover charcoal + the potassium in wood ashes would also encourage new fungal development, which is a critical component to healthy soil.


    Not only does this seem like a plausible method of amendment, it seems like it would have been very effective in the long term as a one-time treatment.