11
The Stability of Biochar in the
Environment
Andrew R. Zimmerman
1,
* and Bin Gao
2
Introduction
1 Biochar Recalcitrance and Lability
2 Biochar Loss—Rates and Models
2.1 Short-Term Laboratory Incubations
2.2 Biochar Mineralization Models
2.3 Field Studies
3 Mechanisms of Black Carbon and Biochar Loss
3.1 Biotic Black Carbon Degradation
3.2 Abiotic Oxidative Black Carbon Degradation
3.3 Non-Oxidative Abiotic Black Carbon Loss
3.4 Black Carbon Loss by Leaching
3.5 Black Carbon Losses by Erosion/Translocation
3.6 Black Carbon Losses by Later Fires
4 Biochar-Soil C Interaction and Stability
5 Mechanisms of Biochar Stabilization
Conclusions and Summary
References
1
Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 112120,
Gainesville, FL 32611-2120; E-mail: azimmer@ufl .edu
2
Department of Agricultural and Biological Engineering, University of Florida, Gainesville,
FL 32611; E-mail: bg55@ufl .edu
*Corresponding author
2 Biochar and Soil Biota
Introduction
Pyrogenic organic matter (OM) is a carbon-rich material that is present in
a variety of forms ranging from lightly charred biomass to charcoal to soot
(Masiello 2004). It is known as ‘black carbon’ (BC) by geochemists and has
come to be referred to as ‘biochar’ when created by pyrolysis in oxygen-
limited conditions. An understanding of the effects of biochar amendment
on soil nutrient cycling, water balance, ecology, soil fertility and other
associated benefi cial properties is still emerging. However, it has long been
clear that biochar, as a relatively refractory form of OM, can be used as a
carbon (C) sequestration tool. That is, biomass C in its pyrogenic form is less
susceptible to remineralization (i.e., conversion back to CO
2
and perhaps
CH
4
) in the environment than its non-pyrogenic form.
Understanding and quantifying the longevity of different types of
biochar in the soil environment is important for a number of reasons. First,
making up between 5–30% of soil and sediment organic C (Skjemstad et al.
2002, Song et al. 2002, Masiello and Druffel 2003), BC represents a large but
poorly quantifi ed portion of the surfi cial global carbon cycle. Atmospheric
CO
2
concentrations and associated climate changes of the past, as well as
the historical record of fi re occurrence, may be linked to the stability of BC
in the environment. And any changes in the incidence of fi re that occur
with global climate change may, through BC, represent either a positive or
negative climate change feedback, depending upon BC-soil-fi re dynamics.
Second, one who amends a soil for the purpose of fertility enhancement with
a specifi c biochar type surely would wish to know how long those benefi ts
could be expected to last. Some of these benefi ts are likely related to total
soil C content, while other benefi ts may be related to other characteristics
of biochar which may change over time (Ding et al. 2010, Graber et al. 2010,
Mukherjee 2011). Lastly and most relevant to the present discussion, the
large scale adoption of biochar soil amendment could potentially offset a
substantial portion of the C released by humans through the burning of
fossil fuels and thus serve as an important climate change mitigation tool. A
recent estimate based on available waste biomass quantities, available land
not already dedicated to food production, and C conversion effi ciencies,
predicted that biochar could offset up to 12% of annual net CO
2
-C equivalent
emissions (Woolf et al. 2010). Additional benefi ts may be derived from
improved water use effi ciencies and, should C sequestration activities be
assigned a monetary value such as by C offset trading, rural economies
could benefi t as well. For this to occur, however, an accurate and long-term
accounting system of the effect of biochar amendments of specifi c types on
soil C would need to be developed.
This chapter is intended to review current knowledge on the stability of
soil-amended biochar C as well as its effect on non-biochar soil C. Aspects

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