Agriculture Reference
In-Depth Information
the relatively high biodegradable soil organic matter (SOM) content of primary forest topsoil
but low available nutrients (requirement for microbial population growth), in contrast to
refractory
Terra Preta
SOM with high available soil nutrient contents. Thus we conclude that
nutrient availability in
Terra Preta
is independent from SOM decomposition. The effects on
soil biology seem to be essential as charcoal has the potential to alter the microbial biomass
(Steiner, et al., 2004a) and composition (Birk, 2005) and the microbes are able to change the
charcoal's properties (Glaser, et al., 2001a). Rondon, et al. (2006) found increased biological
N fixation by common beans through charcoal additions and Gehring (2003) increased
occurrence of nodulating plants in forests on
Terra Preta
than on adjacent soils.
B
IOCHAR
P
ROSPECTS AND
E
SSENTIAL
R
ESEARCH
The global potential of biochar (non fuel use charcoal) reaches far beyond
slash and
char
. Inspired by the recreation of
Terra Preta
, most biochar research was restricted to the
humid tropics. More information is needed on the agronomic potential of charcoal, the
potential to use alternative biomass sources (crop residues) and production of by-products to
evaluate the opportunities for adopting a biochar system on a global scale. Biochar as soil
amendment needs to be studied in different climate and soil types. Today, crop residue
biomass represents a considerable problem as well as new challenges and opportunities.
A system converting biomass into energy (hydrogen-rich gas) and producing charcoal as
a by-product might offer an opportunity to address these problems. Charcoal can be produced
by incomplete combustion from any biomass, and it is a by-product of the pyrolysis
technology used for biofuel and ammonia production (Day, et al., 2005).
The acknowledgement of biochar as carbon sink would facilitate C-trading mechanisms.
Although most scientists agree that the half life of charcoal is in the range of centuries or
millennia, a better knowledge of the charcoal's durability in different ecosystems is important
to achieve this goal. An access to the C trade market holds out the prospect to reduce or
eliminate the deforestation of primary forest, because using intact primary forest would
reduce the farmer's C credits. Fearnside (1997) estimated the above-ground biomass of
unlogged forests to be 434 Mg ha
-1
, about half of which is C. This C is lost if burned in a
slash-and-burn scenario and lost at a high percentage if used for charcoal production. The C
trade could provide an incentive to cease further deforestation; instead reforestation and
recuperation of degraded land for fuel and food crops would gain magnitude. As tropical
forests account for between 20 and 25% of the world terrestrial C reservoir (Bernoux, et al.,
2001), this consequently reduces emissions from tropical forest conversion, which is
estimated to contribute globally as much as 25 % of the net CO
2
emissions (Palm, et al.,
2004).
Today most biomass gasification systems tend to suppress the creation of residuals, like
total organic carbon (TOC) and ashes. C-emission trading options and a better knowledge of
charcoal as soil additive would add value to these residues. Further, this would facilitate the
use of alternative biomass, those which are currently avoided to due their higher TOC
residuals. The tarry vapors constitute a significant loss of carbon during carbonization (Antal
and Grønli, 2003), although representing another valuable product. Despite a lack of research,
