Expert: Henry Boyter - 7/28/2008

Question
I've been reading about charcoal used as a soil supplement (i.e. terra preta).  I've tried it on some highly stressed plants and it has produced amazing results (if that is really the cause).  It looks worthy of experimentation.  At the recommended application rates I could see myself using 500 lbs in a decent DOE trial with 4 varieties of raspberries and soil mixtures.  Producing my own charcoal is a little more involved than I have time for right now, particulary in that quantity.  
Buying bags of Kingsford to grind/crush is possible but then again, my Scots heritage rebels against spending money on something I might be able to get more cheaply.  Charcoal is plant derived and mostly carbon.  Coal is plant derived and mostly carbon--and in some parts still available by the ton.

I started wondering what the difference is between charcoal and coal.  Is the difference structural only or is there a chemical difference as well?  In other words, if you were given a cup each of charcoal dust and coal dust, would you be able to tell them apart and how?

Thanks,

David

Answer
Coal and charcoal are not the same thing, but they are similar.

Coal is formed from organic matter under pressure and temperature and with the exclusion of most oxygen.  Coal is closer to crude oil than it is to charcoal because it was formed over many years.

http://www.planete-energies.com/content/coal/formation.html

http://en.wikipedia.org/wiki/Coal


Charcoal is formed by burning wood in the absence of oxygen over short period of time (compared to coal).  Briquettes are a mixture of charcoal, sawdust and other things.

http://en.wikipedia.org/wiki/Charcoal

The problem is that coal has some compounds in it that may be toxic to the plants, that charcoal will not have.  It will be a different, but similar mix, so you would end up with a different experiment.

You can buy bulk charcoal and since it would not be mixed with sawdust like briquettes, you would not need as much.  I found several links on the internet.

http://www.alibaba.com/catalog/11441833/Hardwood_Lump_Charcoal.html