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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Based on the available public studies charcoal can be considered as inert to microbial degradation with relatively huge half-life times.

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Additional information

Many terms have been used to describe these products of combustion including char, charcoal, soot, graphitic carbon, and black carbon (Jones et al., 1997). Charcoal has been considered to be part of the stable carbon pools of soils, with mean residence times of up to several centuries (Skjemstad et al., 2006). It is relatively inert and thus contributes to refractory soil organic matter (Schmidt and Noack, 2000).Its potential role as a C sink in soils and sediments for long time periods, because its microbial decomposition and chemical transformation is apparently very slow.

In (Baldock et al. 2002)is investigated the mineralization of wood (Pinus resinosa) charcoal heated at five temperatures (200, 250, 300, 3500C) after a 120 days of incubation period, at 250C in the absence of light. The following eight combinations have been tested:

1) Glucose: sand media, nutrient/ solution, glucose.

2) Cellulose: sand media, nutrient/ solution, cellulose.

3) 700C wood: sand media, nutrient/ solution, unaltered wood (heated to 700C).

4) 1500C wood: sand media, nutrient/ solution, wood thermally altered at 1500C.

5) 2000C wood: sand media, nutrient/ solution, wood thermally altered at 2000C.

6) 2500C wood: sand media, nutrient/ solution, wood thermally altered at 2500C.

7) 3000C wood: sand media, nutrient/ solution, wood thermally altered at 3000C.

8) 3500C wood: sand media, nutrient/ solution, wood thermally altered at 3500C.  

 

At the end of the incubation period the mineralized organic C (% of initial organic C) found to be below 2 % for the thermally altered wood. 

 

In (Hamer et al. 2004)is investigated the influence of14C-glucose addition on the mineralisation of charred maize and rye residues (thermally altered at 350oC) and oak wood (thermally altered at 800oC). The different BC materials were mixed with sand and incubated for 60 days at 20oC. The samples received 20μg glucose-C per mg black carbon at the beginning and at day 26 of the experiment. At the beginning, a nutrient solution [(NH4)2SO4+KH2PO4] and an extracted from an arable soil were added. A mineralization of0.78%, 0.72% and 0.26% for charred maize, charred rye and charred oak respectively has been observed.

 

In (Nocentini et al. 2010) is investigated the mineralisation of charcoal during a 1 month incubation experiment using microbial inocula extracted from burned and unburned soil, under controlled conditions with and without substrate addition.

Artificial charcoal was produced in the laboratory starting from pine needles and pine wood, to create optimal conditions for microorganisms, the flasks with charcoal and sand were incubated at 50% of WHC at 200C in an incubation chamber. At the end of the month5.7 mg CO2/g C of charcoal (inocolum from unburned soil) has been measured.

 

In (Kuzyakow et al. 2009)the decomposition rates of BC were estimated based on14CO2sampled 44 times during the 3.2 years incubation period (1181 days).

The decomposition rates of BC calculated based on14C in CO2were similar in soil and in loess and amounted to 1.36 10-3%d-1. This corresponds to a decomposition of about 0.5% BC per year under optimal conditions. Considering about 10 times slower decomposition of BC under natural conditions, the mean residence time (MRT) of BC is about 2000 years, and the half-life is about 1400 years.

 

In conclusion charcoal can be considered as inert to microbial degradation with relatively huge half-life times.