Experimenting with Biochar: pursuing the promise of charcoal as a soil ammendment

char header I have this neighbor up here.  He’s always saying sustainability and permaculture and stuff like that, but I was surprised in a recent conversation to find out that he did not know the term, or concept of, biochar.  For others who don’t know, that’s a catchy marketable name for charcoal that is intended as a soil amendment, the claimed benefits of which I’ll delve into further on.  I’m not even sure I like the term biochar.  Why name something that already has a name?  Maybe so you can market it?  Charcoal with special properties?  Anyway, I guess I thought it was more in peoples consciousness than it probably is, and since my sustainably hip neighbor was unfamiliar with the concept, I got to wondering how many other people haven't yet encountered the concept and thought I’d present some thoughts and information here in case I might be able to convince more folks to delve into experimenting with the idea.

I had seen some interesting, and even exciting, articles and videos on using charcoal as a soil amendment.  But, all the references were based on the discovery of terra preta, which are these human modified soils in the Amazon containing a large amount of charcoal.  The claim is that these soils are still highly fertile compared to the natural soils surrounding them, even after many hundreds of years of heavy Amazonian rains.  The mysteries of terra preta are still being prodded and examined, but clearly charcoal is a major player, and likely the key ingredient.  If it functions as advertised, adding char is a permanent improvement, unlike the treadmill of organic matter and nutrients that we add to our soils every year and which mostly flush away in the rain.  I've seen what happens to gardens when they are abandoned.  The fertility quickly declines remarkably fast and eventually disappears.  The possibility of making really permanent improvement to gardens, orchards and pastures is very compelling and worth some great effort.

Having trained myself to be somewhat cautious and critical of new and exciting ideas, I was naturally slow to adopt.  I was very interested though and began to save any charcoal I could for experimenting.  One day while researching heirloom apples, I found a 19th century reference to using charcoal in potting soil, which gave me the idea to search google books for the terms - charcoal fertilizer - ,.  I limited the search to the 19th century.  Bingo!  I found a bunch of very interesting references. Now that I had something besides the much recycled terra preta hype to fuel me, I was much more excited to experiment.  If you haven’t read that post, you totally should.  It’s quite fascinating.  You can skip my usual rambling and go straight to the accounts.  Biochar use in Europe and North America in the 19th century.  Since most of you won't actually click the link and read it, here is a tasty extract...


The Farmers’ cabinet, and American herd-book, Volume 11 From the Farmer and Mechanic Comparative Merits of Charcoal and Barn-yard Manure as Fertilizers. In the year 1788, my father purchased and removed upon the tract of land in Hanover township, Morris county, N. J. The land, owing to the bad system of cultivation then prevailing, was completely exhausted, and the buildings and fences in a state of dilapidation. The foundation of the barn was buried several feet beneath a pile of manure, the accumulation of years: little or none ever having been removed upon the lands. Even the cellar, beneath the farm-house, was half filled with the dung of sheep and other animals, which had been sheltered in it. The former occupant of the farm had abandoned it on account of its supposed sterility, and taken up the line of march for the Valley of the Miami, along with the first caravan of pioneers who accompanied Judge Symmes.

The barn, before referred to, was removed to another situation soon after its foundation was uncovered, by the removal of the manure to the exhausted fields; and its site, owing to the new arrangements of the farm, became the centre of one of its enclosures. During the seventeen years which I afterwards remained upon the farm, the spot could easily be found by the luxuriousness of the grass, or other crops growing thereon; though the abatement in its fertility was evident and rapid. On revisiting the neighbourhood in the autumn of 1817, I carefully examined the corn crops then standing upon the spot, and was unable to discover the slightest difference in the growth or product, upon that and other parts of the field. This was about twenty-eight years after the removal of the barn.

Upon the same farm and upon soil every way inferior, were the remains of several pit-bottoms, where charcoal had been burned before the recollection of any person now in the vicinity, and most probably, judging from appearances, between the years 1760-70. These pit-bottoms were always clothed, when in pasture, with a luxuriant covering of grass, and when brought under tillage, with heavy crops of grain. Eleven years ago I pointed out these facts to the present occupant, and his observations since, coincide with my own, previously made; that they retain their fertility, very little impaired, a period probably of about seventy or eighty, certainly not less than sixty-five or seventy years. Here then is an excellent opportunity of observing the comparative value of charcoal and barn-yard manures, as a fertilizer of lands. The former has not, after at least sixty or seventy years exposure, exhausted its powers of production, while the latter lost its influence entirely in twenty-eight years, and most probably in much less time.

I have since had many opportunities of’ observing the effects of charcoal left in pitbottoms, upon vegetation, one of which only,. I will relate. The last season, in the northern part of Ohio, was one of uncommon frost and drought . In May, the wheat fields, when promising a luxuriant crop, were cut off by frost;—especially in the valleys, and very much injured in the high lands—which was succeeded by the most severe drought ever experienced in the West. The moiety which escaped both these scourges, was afterwards very much injured by rust. Near the village of Canton, upon a farm on high ground, which had been mostly cleared of its timber by its conversion into charcoal, it was observed that upon the old pit-bottoms, the wheat grew very luxuriantly—was clear of rust—and had ripened plump in the berry; while in the adjacent parts of the field it was short in growth, the stem blackened with rust, and the berry light and shrivelled."

All the results are definitely not in on using charcoal as a soil amendment.  It is being sold as a panacea for the ills of the planet and human society, and large corporate interests are even becoming involved.  The biggest claim is that charring gajillions of tons of woody debris and burying it can help mitigate climate change.  About half of the carbon in woody material can be converted into charcoal, an extremely durable material capable, at least in some cases, of residing in the soil for thousands of years.  Not only that, but if that buried charcoal increases plant growth and fertility, as it is claimed, the extra abundant growth on previously less fertile soil will absorb even more carbon which could then be charred as well.  If the wood decays naturally, little of the carbon remains in the soil, but instead ends up back in the atmosphere.  While it seems hard to believe we could char our way out of the enormous quantities of carbon we've released in the last 00 years of so of burning fossil fuels, that is the hopeful claim of many biochar champions.  Other claims, relevant to us as gardeners, are increased water retention in the soil, reduced leaching of nutrients (because they bind strongly to the charcoal which is a virtual magnet for all types of substances) and therefore a decreased reliance on fertilizers, better and earlier soil warming, and Increased microbial activity (the miles of pore space and surface area in a piece of charcoal, rich with absorbed nutrients, providing a huge habitat for living things.).  One issue though, is how char will work when applied to differing soils in various climates.  The truth is that there is a lot we don’t know about the practical applications and benefits under varying circumstances. carefully designed long term studies might help, but If we wait for science, and possibly more relevant, its interpreters, we may be disappointed or behind the curve.  Besides, there are so many climatic/gardening style/fertilizer and soil type factors to account for.  You and I only have one agenda, to see if the stuff works in our soils and gardens.  I suspect that it will work for some of us, so lets just find out on our own.  It’s not really that hard to just try the idea out in small areas.  If charcoal amended areas of our garden consistently grow the giganticest healthiest plants ever, that's probably a green light to keep burying charcoal.

The first idea I was able to reject in order to move on was the idea that I needed special charcoal, burned in a special way.  The 19th century references were using whatever charcoal was available.  Most of it was probably slow burned in piles since that was the common method, but I feel pretty sure that whatever charcoal we can come up with is probably worth trying, even if it isn't ideal, (which I've seen no compelling evidence so far to say it's not.  Not that I've looked very hard).  It takes a lot of charcoal to reach a soil content of 10% in a significantly large area.  Save charcoal wherever you can get it.  Avoid the moulded “charcoal” briquets that people use to barbeque.  Those are made with coal and are actually “coke” briquets (coke is the term for the equivalent of charcoal made from coal).  I have been partially successful at convincing others around here to save the charcoal from the woodstove every morning, which adds up over a winter.  I also collect it from campfires and burnpiles.  Once a burn pile is down to just embers, it can be spread out and/or doused with water to prevent the charcoal from burning all the way down to ash.

this picture is just to keep you interested in case you have a short attention span ;)

I’m also planning to produce charcoal intentionally.  I have this friend that is always telling me about the newest best thing ever.  Biochar is one of them.  While this guy is much less cautious than me in accepting an idea as worth pursuing, while I was still getting excited about biochar, he was making 17 yards in one winter!  The guy gets mad respect for GSD (getting shit done) and pursuing his goals for self reliance.  Charcoal has traditionally been a very polluting activity producing enormous quantities of very dirty smoke.  This friend burns his in a barrel with a flue on top, which burns much cleaner than traditional methods of smothering.  He learned the method from this video.  The technique could no doubt be refined, but it is where I’ll be starting.  I'm also hoping to adapt the same kiln for lime burning, or making char and sea shell lime at the same time.  My friend added a fan which feeds into the bottom of the barrel.  Most other methods burn up some fuel all the way to ash in order to make the charcoal, but this kiln achieves two very important goals relatively well, efficient fuel use and low emissions.  I have some barrels and, time and energy permitting, I’ll be setting up a couple of these kilns and charring some wood chips.

My soil amending experiments have just begun.  This spring I ground up and buried some charcoal in a garden bed.  I divided this long bed into three 7 foot long sections.  Section one has about 10% charcoal in the top 10 inches of soil.  Section two has 5% and section three has none.  It is generally said that a certain percentage is required to start seeing real benefits, so adding a quantity to a small area rather than just spreading it out over a whole bed or garden seems like the way to go.  Some say that the charcoal should be pre-charged with nutrients because it is so adsorptive of plant foods that it will deplete the soil at first until an equilibrium is achieved.  I chose not to pre-charge to see what would happen, and so I could treat the control section the same as the charcoal sections.  I also dug the no-char section just the same as the other two sections, even going so far as to go through the same motion of sifting in the char that wasn't there.  I did add a sprinkling of woodash to the no-char section to try to imitate the small amount of ash present in the pulverized charcoal.

2x4's are use to roughly measure the depth of the charcoal.

char spread out

This experimental bed was planted to peas, spinach and lettuce, with the rows running the full length of the bed.  At first things grew well, but as time went on, it was apparent that the more charcoal there was in the soil, the less the lettuce and spinach grew.  The 10% charcoal end of the bed was a total loss as far as lettuce goes.  The Peas did okay through the whole bed, but not great.  It was difficult to discern much difference, but that was complicated by part of the pea row being attacked by birds and bugs.  Anyway, it appears that it is probably true that the charcoal should be pre-charged or it will sap the soil of nutrients in the beginning.  I would probably charge by mixing with compost or soaking in compost tea, except that sort of screws up the experiment of doing the same thing to all areas of the bed except for the charcoal content.

Although I’m very excited about biochar and plan to scale up production and experiments, I will approach it somewhat cautiously at first since it is a permanent addition and can’t be undone.  I will continue to plant primarily test plots as outlined above, but with variations in depth and quantity of charcoal.  Next I’d like to do a bed that has charcoal at varying quantity, up to 20%, but 24 inches deep instead of 12, and one with the same quantity of charcoal in each section, but dug in to various depths.  I also plan to bury some in the meadow to see the long term effects there.  finally, I’d like to see what happens if I just throw the stuff down on the meadow without burying it.  I plan to do dug control plots in all cases, because that eliminates the possibility that it is just the act of digging that is making a difference.  These few simple tests should yield up some fundamental information that can tell me whether to proceed to char everything I can get my hands on, or spend my time on something else.

If you can collect charcoal from burn piles, campfires or the woodstove, it doesn’t take all that much to put together a very small test plot.  It probably should be used in adequate quantity per area.  10% would be something around one and a half inches deep dug into 12 inches of soil.  I’m mostly planning to use 5%, 10% and 20%.  Grinding the charcoal can be a problem.  I have been using an old corn, bone and shell mill that someone gave me.  It grinds the charcoal to pea sized and down, which is what I decided I want for now, though it could be adjusted finer or coarser.  I’m tempted to do some tests with various sized grinds, and probably will eventually.  a hammer mill of the garden variety chipper shredder type would probably work and I’ve thought about running it over with a car or a heavy roller of some kind.

The Enterprise corn, bone and shell grinder in use for grinding oyster shells.  Works great for charcoal.

My first experimental bed is now planted to leeks for the winter as it's second crop.  I’ll continue to plant the whole bed uniformly to the same crops for comparison, and I hope by next growing season to be able to discern any obvious effects.  When you realize how much charcoal it actually takes to amend 100 square feet at even just 5%, you may be discouraged, but remember that this is potentially a permanent soil improvement.  Remember too that It can also be done in small sections as charcoal becomes available, so there is not necessarily a need for a heroic effort.  If it really is as useful as we all hope, it is also quite possible that it will be worth buying the charcoal if need be, though it seems ideal to figure out how we can char whatever debris we might have on the home place, including crop wastes.  Since the process produces quite a lot of heat, there seems to be great potential for working charring into home systems.  For instance one could potentially heat water, boil bark for tanning skins, make lime, cook, can food, dry food, heat greenhouses, heat living spaces, etc... all while producing char.  The trick is going to be figuring out char producing stoves and kilns of various kinds for these purposes, which use the fuel sizes and shapes that we have available.  Once that is figured out though, charring, rather than being an extra job will be integrated into homestead life.  That's a pretty neat vision.

Posted on October 15, 2013 and filed under Garden Stuff, Uncategorized.