[Golfer]

I live near an iron furnace that operated for about 50 years during
the 18 century located in the mid-Atlantic states in the USA. I
decided to take a soil sample of charcoal from this old furnace and
have it analized by my local agricultural university. But first, I
will describe the condition of the site and its charcoal.

The site is now in the middle of a hardwood forest with trees
averaging about a foot in diameter. There is lots of what appear to
be ground charcoal located just beneath a layer of leaf litter
concentrated in a 20 by 50 foot area near the old furnace. The
charcoal appears to be ground very fine and it is interlaced heavily
with roots. When first dug from the ground, much of it is bound into
fist size clumps that break apart easily when tapped with fingers.
When handling this charcoal, it feels silky like graphite. It
quickly turns the hands filthy and black. If sifted, the charcoal
will yield some pieces about the size of a cubic centimeter.

I was very curious to see what the charcoal from around this site
might have in common with terra preta. It may be one of the oldest
concentrations of man-made charcoal in the USA. The results from the soil
test are as follows:

P(lb/A)=16, K(lb/A)=160, Ca(lb/A)=3317, Mg(lb/A)=254,
Zn(ppm)=0.7 Mn(ppm)=3.5 Cu(ppm)=0.1 Fe(ppm)=0.4
B(ppm)=0.7 S. Salts(ppm)=115

Soil pH=7.0 Est. CEC(meq/100g)=9.5

Base Sat.= 100% Ca Sat.=86.9% Mg Sat.=11.0% K Sat.=2.2%

Organic Matter= 18.9%


The local soil tends to be acidic and sandy. It supports blueberries, huckleberries, mountain laurel, rhododendron, and holly trees (under the oak/hickory cannopy).

[Essay]

This strikes me as very interesting ...and thanks for the great descriptions.

I googled to find out what the CEC of "good soil" is, and came up with some neat info. The first link wouldn't work, so I just copied the search result.

ftp://ftp-fc.sc.egov.usda.gov/GLTI/t...h/nrph-ch3.pdf
Ecological Sites and Forage Suitability Groups:
Plant-soil moisture relationships are good. Soil surface is. dark colored and has a crumbly structure. ...... native pH below 5.5 and a CEC greater than 7
...but the other link worked....

http://www.plantstress.com/Articles/..._fertility.pdf

The CEC affects the way a soil should be managed for crop production and environmental protection. For example, a soil with a low CEC (less than 5 meq/100g) generally has a low clay and organic matter content, has a low water holding capacity, requires more frequent lime and fertilizer additions, and is subject to leaching of NO3, B, NH4, K and perhaps Mg. Such soils will have lower yield potential than soils with higher CEC under the same level of management, but high productivity can be maintained by intensive management. These soils will usually be easier to cultivate than soils with higher CEC since they drain more rapidly, and added nutrients are highly available for plant uptake. Soils with CEC greater than 20 may have high clay content, moderate to high organic matter content, high water holding capacity, less frequent need for lime and fertilizers (except N), and low leaching potential for cationic nutrients. On the other hand, their physical properties may make it difficult for a farmer to cultivate, irrigate or maintain good aeration. Such soils are also more prone to K fixation unless soil K levels are inherently high.

The base cations include K, Ca, and Mg, (and Na, when present) and the base saturation is the proportion of the CEC occupied by these base cations. For a soil with 0.5 meq of K, 2.1 meq Ca, 0.4 meq of Mg and a CEC of 4.0 meq/100g , the base saturation is: (0.5 meq K + 2.1 meq Ca + 0.4 meq Mg) / 4.0 meq CEC = 3.0/4.0 or 75%. A relatively high base saturation of CEC ( 70 to 80%) should be maintained for most cropping systems, since the base saturation determines in large measure the availability of bases for plant uptake , and strongly influences soil pH as well. Low base saturation levels will result in very acid soils, and potentially toxic cations such as Al and Mn from the soil (Chapter 3).

Anion Exchange: Although the extent of positive charge on the soil is seldom as large as the negative charge, broken edges of kaolinite and iron and aluminum minerals in soils of the southeastern US can develop positively charged sites as the pH begins to drop below 5.5. These positively charged sites can be significant in the retention of sulfate and phosphate, especially in subsoil clay layers where pH is normally unaffected by liming.
===

Very interesting....

Your description of the sandy, acidic surrounding soil sounds as if it would test very differently than the soil you tested.

I do wonder if there might be some other heavy metals in the soil. Aren't those usually found around smelters (is that what this "furnace" was?).

Hope to see some further updates, if possible.

Thanks,
~SA

[Golfer]

The furnace was what is called a tubal furnace. It was used to convert iron ore into pig iron and cast iron items such as shovels, frying pans, and cook pots. Charcoal was fired elsewhere and brought to the furnace. Charcoal was made by professionals called colliers. They carefully stacked short lengths of wood in a circle up 50 feet wide and about 8 feet tall and left an open space in the middle to serve as a sort of chimney. This mound of wood was then covered in a layer of leaves and then a layer of soil. A fire was set in the chimney hole and it slowly converted the wood to charcoal. I don't know how hot the fires in these charcoal operations burned. I wonder how this charcoal compares to the Amazonian charcoal in terra preta. The charcoal was then ground and added to the furnace for iron ore smelting.

The site from which the charcoal sample came is what I believe was a place where charcoal was stored until needed. It is located above the furnace and contains no slag (that I have seen).

The results of the test suprised me. The sample had an organic matter content of 18.9%. That is very high. However, the CEC was only 9.5; that's not much better than fine sand. I understood that high organic matter always equaled a high CEC. Does this mean that this charcoal couldn't contribute much in the way of fertility? Keep in mind that this stuff could be over 200 years old, so it has had lots of time to weather. Are there other tests I could subject this stuff to?