FAO - Making charcoal in earth mounds
The alternative to digging a pit is to stack the wood above the ground and cover the stack with earth. This method is also very old and is widely used in many countries. One finds many variations of the basic method. Studies have been made in some countries to optimise the design. The Swedish work in this area some years ago is notable. Essentially the process is the same as the pit - the wood to be carbonized is enclosed behind an air-tight well made from earth, a universally available material wherever wood is grown. The earth mound is preferred over the pit where the soil is rocky, hard or shallow, or the water table is close to the surface. By contrast the pit is ideal where the soil is well drained, deep and loamy. The mound is also more practical in agricultural zones where fuelwood sources may be scattered and it is desirable to make the charcoal near a village or other permanent site.
A mound site can be used over and over again, whereas pits tend to be used a few times and then new ones dug to follow the timber resource. Also where the water table is close to the surface or drainage is poor, pits are not practical. The repeated digging of pits also disrupts cultivation for crops or pasture. The fuelwood to be carbonised, in a mound can also be gathered slowly over a period of months, stacked in position and allowed to dry out well before covering and burning. This fits in well with the life style of a small farmer who may gather scrap wood, branches and logs and stack them carefully to form the mound. After some months, depending on the season, charcoal prices and so on, he covers the mound with earth and burns the charcoal. A small cash income is produced this way which requires no initial cash outlay.