[Turtle]

Originally Posted by Pangolin

...
As a means of understanding the uses of Terra Preta it would be usefull to know [i]how much we need for the job[/a] i.e. reducing atmospheric CO2 and/or improving farmland. It would be helpful to know this in units that are in use by the layman i.e. cubic yards of charcoal. It would also be usefull to know minimum and maximum usefull application spread rates in acres and or/sq ft. Just like any other soil amendment.

The current situation is that we have no definitive answers to these questions. It is experiments and reporting on those experiments by interested folks like you that may change that.

For the agricultural side, get some charcoal, measure its volume after crushing it into variable sizes from powdery to around 3mm, and then weigh it. I would suggest mixing it at a rate of 20% by volume of your existing soil. Then grow as usual and note any differences.

I haven't run across the actual carbon content of charcoal(s)*, but finding that, then you can calculate how much carbon you have sequestered. In one of the threads here on terra preta - or a link in one - it was suggested we would have to bury the charcoal to a 3 foot depth on current agricultural land. For simple sequestering purpose, we needn't use only agricultural lands I think.

*Post Script: It's not as simple as it may seem. Bold emphasis mine. >>

Originally Posted by springerlink.com

Abstract Diffuse reflectance Fourier transform infra-red spectroscopy (DRIFT) has been used to characterise the chemical nature of a range of charcoals produced from different woods and with differing carbon contents. The technique is simple to perform and high quality spectra are reported for total carbon contents of up to 92.5%. The work shows that carbonisation of wood results in a graded change in chemical nature from a material rich in aliphatic structures to one dominated by aromatic domains as carbon content increases.

SpringerLink - Journal Article

[Philip Small]

Originally Posted by Pangolin

At the average density of hardwood charcoal what volume of ...

I read through the thread a little quickly, so apologies if bits of this this has already been covered.

Charcoal is carbon with minor impurities so it is reasonable to assume for our purposes that a ton or yard of charcoal is a ton or yard of carbon.

Carbon dioxide units at full molecular weight can be converted into equivalent carbon units by dividing by 44/12 (see endnotes here).

A metric ton of charcoal is equivalent to 3.67 metric tons of carbon dioxide.

A cubic yard of hardwood charcoal weighs about 475 lbs. (based on one (1) 8.8 lb, 0.5 cu ft, bag Cowboy brand hardwood charcoal) >> Revised per new information and correct calculations: A cubic yard of charcoal, at 250 kg/m3 weighs 148.6 lbs.

A ton of charcoal is about 13.5 yards.

A metric ton of charcoal is about 14.8 yards.

A metric tonne of carbon dioxide contains about the same amount of carbon as 4.04 yards of (pure carbon) charcoal.


Corrected lb/ft3 per formula kg/m3*2.2 lbs/kg*(((0.3048 m/ft)*3ft/yd)^3)m3/ft3=lbs/ft3. lbs/ft3 * 27 = lbs/yd

[Turtle]

I have some 'horticultural charcoal' still left, so I weighed it.[bag says Product of USA, Red McLellan Co, Whitney Farms, PO Box 70, Independence, OR 97351, Whitney Farms Organic Garden Products Mind you, particle size IS extremely important to weight per unit volume, and I will have those experiment results presently.

Since my source shows the highest carbon content charcoal is only 92.5% carbon, I think Phillip's estimates are too large.

So, 1 cup of 'horticultural charcoal' pieces in the 1cm to 2cm size range weighs 93.272gms.

1 cup of my native soil weighs 242.354gms

I have 1/2 cup of the charcoal bits in my mortor, and I will measure the volume after crushing them to fine particles. Regardless of what the other fellas tell you, size matters.

[Philip Small]

Originally Posted by Philip Small

A metric tonne of carbon dioxide contains about the same amount of carbon as 4.04 yards of charcoal.

Revised to 4.25 yards of charcoal needed to offset a metric tonne of carbon doxide.

Carbon content of charcoal appears to be between 95 and 99 percent (see here). The 1-5% is ash and non-C components of volatile/aromatic constituents. At 95% C, it takes 4.25 yards of charcoal. (see additional revision in later post)

The density of charcoal used in the previous post (17.6 lbs/ft³) does not seem to bear out in other references:
Density of charcoal is expected to be between 250 kg/m³ (5.5 lb/ft³) and 300 kg/m³ (6.6 lb/ft³). Rail freight for charcoal is calculated on the basis of 300 kg/m³ of charcoal.


Corrected lb/ft3 per formula kg/m3*2.2 lbs/kg*(((0.3048 m/ft)*3ft/yd)^3)m3/ft3=lbs/ft3.

[Philip Small]

Originally Posted by Philip Small

Revised to 4.25 yards of charcoal needed to offset a metric tonne of carbon doxide.

Revised (yet again) to 4.64 yards of charcoal needed to offset a metric tonne of carbon dioxide, per carbon content of charcoal at 87 percent. (pdf source)

Note: corrected per conversion error

[Turtle]

Originally Posted by Philip Small

Carbon content of charcoal appears to be between 95 and 99 percent (see here).

I see only the 92% figure at your link; in the table and associated with 700degC process.

Originally Posted by Phillip

The density of charcoal used in the previous post (17.6 lbs/ft³) seems to bear out in other references:
Density of charcoal is expected to be between 250 kg/m³ (15.6 lb/ft³) and 300 kg/m³ (18.7 lb/ft³). Rail freight for charcoal is calculated on the basis of 300 kg/m³ of charcoal.

Accessing... I'll scale up my measure to compare with your accredited figures.

So again, the particle size matters! A lot! The 'standard' ratings of so many tons per this or that conveyance are of little worth if the particle size is not noted. My 1/2 cup of 2 to 3cm pieces ground down to 1/3 cup of sub-milimeter chunks and powder. A reduction of 1/3 in volume with no change in weight.

Also, the % of carbon is highly variable depending on the specific wood used and the temperature used to cook it. If we want a real idea of the answer we need the variability of each factor plotted as a graph and then all against each other ala linear programming.

[Turtle]

Originally Posted by Turtle

Accessing... I'll scale up my measure to compare with your accredited figures.

Scaling my actual measure for charcoal of 93.27 gms/cup to kg/m³ gives a figure of 230 kg/m³ (5.07 lbs/foot³; 137 lbs/yard³) for density of horticultural charcoal chunks in the 2cm to 3cm range.


Work >> 1 cup charcoal weighs 93.272 gms * 16 cups/gallon = 1,492.35gm/gallon * 7.48 gallons/foot³ = 11,162.79 gm/foot³ / 1,000gm/kgm = 11.16279 kgm/foot³ / 2.2 lbs/kgm = 5.07 lbs/foot³ * 27 foot³/yard³ = 136.99 lbs/yard³ * .765 = 104.79 lbs/m³ * 2.2 kgm/lb = 230.5 kgm/m³

[Philip Small]

Originally Posted by Pangolin

What is the maximum reasonable charcoal input on a given acre of land?

Considering the theoretical scenario presented, you could reasonably add charcoal at 1 ton/acre/year. forever. to any reasonable soil, not just agriculture. Considering that charcoal could reasonably be employed in strategies to vegetate non-soil and disturbed soil areas (active sand dunes, recent lava flows, badlands, damaged and degraded landscapes) it is reasonable to cast a wide net when defining what qualifies as "a given acre".

The surface 3.3 inches of mineral soil weighs about 1 million pounds per acre (calculated as 2.65 gm/cm3 (quartz IIRC) * 50% soil porosity * 2.72 million pounds water per acre foot. Note: clays are lighter, sands are heavier due to 60 and 40 percent porosity, respectively)

so a ton of charcoal per acre would increase soil charcoal content in a typical mineral soil by 0.2 percent, or 2 g/kg, in the top 3.3 inches.

At 5.05 lbs/ft3, 1 ton/acre of charcoal would be 1 tenth of an inch deep.

Revised per corrected conversion for lbs/ft3

[Philip Small]

Originally Posted by Pangolin

How much agricultural land in the world do we have that we could reasonably use for Terra Preta sequestration?

According to this source, of 1.5*10^8 km2 land, 30% is good for agriculture. If we add in the topsoil-less land, the dry land and 1/2 the mountains, we increase terra preta reasonable candidate land to 70%, or 1.05*10^7 km2.

This is equivalent to 2.72*10^6 mi2, or 1.74*10^10 acres

[Philip Small]

Originally Posted by Pangolin

What is the net annual increase in [excess] carbon?

Around 24.126 billion tonnes of CO2 are released from man made carbon dioxide sources per year worldwide, equivalent to about 6.6 billion tonnes of carbon.