Agriculture Reference
In-Depth Information
Slash and Char
was described as an alternative to slash and burn (Lehmann, et al., 2002)
and (Steiner, et al., 2004b) observed that charcoal is currently used by Amazonian settlers to
improve soil fertility. If a forest is burned, only around 2-3% of the above-ground C is
converted into charcoal (Fearnside, et al., 2001), but charcoal production can capture 50% of
the above-ground C. If the charcoal is not used as fuel (e. g., soil amendment) it has a very
high recalcitrance against biological or chemical decay and stores the carbon over centuries or
millennia.
Slash and char
is an alternative agricultural method producing charcoal out of the
aboveground biomass instead of converting it to CO
2
through burning. If re-growing
resources are used,
slash and char
could establish as a significant carbon sink and could be an
important step towards sustainability and SOM conservation.
On a global scale, the total carbon release flux due to fire is of the order of 4-7 Pg of
carbon per year. This flux is almost as large as the rate of fossil fuel consumption (about 6 Pg
per year in 1990) (Goudriaan, 1995). Fearnside (2000) calculated a total net emission of
carbon from tropical land uses, equivalent to approximately 29% of the total anthropogenic
emission from fossil fuels and land-use change. These numbers emphasize the potential for C
management if only biomass is utilized being ablaze each year.
As a result of intensive research done in the 1980s, carbonized materials are formally
authorized for use as soil amendment material in Japan. Thus Japan used 27% of the total
charcoal consumption (50,835 Mg in 1999) for purposes other than fuel. By far the biggest
proportion was used for agriculture (30.6%) followed by livestock industries (22.3%),
gardening and golf courses (7.6 %) (Okimori, et al., 2003). A Japanese company established
charcoal production at an Indonesian tree plantation for pulp production. Their feasibility
study with conventional charcoal-making methods showed that 77,000 Mg charcoal could be
produced per year, and the carbon emission reductions by the project reaches 62,000 Mg C
yr
-1
(= 230,000 Mg CO
2
yr
-1
) at an annual wood harvest of 10,000 ha (Okimori, et al., 2003).
S
OIL
F
ERTILITY
E
NHANCEMENT
Antal and Grønli (2003) mentioned that most potting soils, herbicides in carbon-based
formulations, and culture media formulations contain charcoal or activated carbons, although
the scientific rationale for these applications is absent. Recent studies showed that soil
charcoal amendments are indeed capable of increasing soil fertility. Charcoal significantly
increased plant growth and nutrition in a pot experiment by Lehmann, et al. (2003) and a field
experiment by Steiner, et al., (2007c). The authors proposed that charcoal can improve soil
chemical, biological, and physical properties, but could not completely discern the
mechanisms of fertility enhancement. Lehmann, et al., (2003) found significantly reduced
leaching of applied fertilizer N in charcoal containing pots. This was corroborated by the
findings of Steiner, et al., (2007a in submission) and Steiner, et al., (2007b in submission).
Soil respiration and the microbial population growth rate were found significantly altered
by charcoal amendments. Steiner, et al., (2004a) found increased microbial activity on
charcoal amended plots.
Terra Preta
soils were marked by a very low soil respiration but very
high population growth after substrate (glucose) additions. Unmanaged forest soils (Ferralsol)
had a higher respiration rate but a very low population growth potential. These results reflect
