Ash is a solid, particulate, inorganic combustion
residue. The ash content varies greatly between different fuels.
Of forest fuels, ash content varies between different components,
stemwood 0,4-0,6%, stem bark 2-5% and 1-2% branches. The ash
content is highest in those parts of the tree where growth occurs.
In the leaves, needles and branches and leading
shoot varied between 2 and 6%. As a mean value of forest fuels
can be expected 1-2% ash content. All values are calculated
on the fuel solids. Ash from the wood fuel contains nutrients
which the tree raised, including important trace elements. Nitrogen
(N) is missing because it largely leaves in gaseous combustion.
Since trees take up heavy metals and radioactive
substances from soil and air, are also those substances in the
ash. Generally, the ash is between 10% and 30% of calcium (Ca).
The content of potassium (K) and magnesium (Mg) is usually a
few percent, while the phosphorus (P) represents approximately
one percent of the total content.
Most of these substances have been lime-acting
nature and occurs both as soluble salts, as well as more insoluble
compounds in the form of oxides, hydroxides, carbonates and
silicates. Ashes from the incineration of wood generally have
a pH between 9 and 13.
The lime effect and nutrients in the ash makes
it suitable to use to compensate for losses of such substances
in the woodland. The law consider ash as a waste. That is why
we must have a permit to store it.