The other big issue to address concerns the soil loading capacity for biochar
(BLC) or in another way, the question of how much biochar soil can tolerate. Soils
with high biochar concentrations corresponding to about 40% of their soil organic
carbon were found in the Amazonian Basin. Furthermore, after hundreds or thousands of years, the productivity of these soils did not decrease or even increase. The
evidence available points out, for example, that in a weathered tropic soil, crop
yields kept increasing with biochar loadings up to 140 t Cha
−1 . On the other hand,
other trials showed that some crops delivered positive effects concerning biomass
and yields, at much lower applications. For example, experiments with bean
(Phaseolus vulgaris L.) cultivation showed positive yield effects with application
rates up to 50 t Cha
−1 , which disappeared with a rate of 60 t Cha
−1 , along with yield
decreases at application rates of 150 t Cha
−1 . This is indicative that BLC is likely to
be dependent on crops, on soil and climate, and on rates of application and total
accumulated amounts as well. Overall, it is likely that crops respond positively to
biochar additions up to 50 t Cha
−1 with possible growth reductions at very high
rates of application.
Smoldering combustion is another variable interfering with BLC, insofar that this
kind of combustion can be supported for years or long time periods in organic soils
that dry out sufficiently. Thus, soils with extreme loadings of biochar, subjected to
drastic drying conditions, could eventually withstand smoldering fires ignited by
natural or anthropogenic factors. This is an issue also requiring long-term research.
The sum of downward CO 2 from the atmosphere to the ocean, soil, and vegetation is of the order of 213.35 GtC, and the sum of upward fluxes to the atmosphere
of non-anthropogenic sources which were soil, vegetation, oceans, and forests
accounts for about 211.6 GtC, so that e.g. in 2004 a net loss of carbon from the
atmosphere was of around 1.75 GtC. This loss was however more than compensated
by anthropogenic sources of 5.5 GtC, delivering to a net gain of around 3.75 GtC, for
which a significant contribution for mitigation could be achieved through biochar
addition in soil. The hypothetical equilibrium of anthropogenic carbon emissions
should be thereby the main objective to achieve with biochar in soil (e.g., Verheijen
et al. 2010). As aforementioned, the carbon dioxide emissions were higher of around
9.9 GtC in 2017 and averaging 4.7 GtC in the period 2008–2017.
Also, global emissions of greenhouse gases were reported as increasing by 35%
from 1990 to 2010 reaching about 13.6 GtC. These later data ranges from 0.4 to 2.5
orders of magnitude from the value of 5.5 GtC of 2004, a variation which is not
incompatible with the hypothetical equilibrium role of compensation, already
mentioned, are attributed to biochar. Estimations were carried out indicating that
storing carbon in biochar would compensate global carbon yearly emissions of
about 0.1–0.3 Gt CO 2 .
Other projections mention that carbon sequestration of biochar, resulting from
forestry and agricultural residues and urban wastes, would reach by 2100 yearly
values ranging from 5.5 to 9.5 Gt C, values of the same order of magnitude of
current fossils fuel emissions. Also, an application of 10–100 Mgha
−1 of biochar,
with carbon concentration around 50–78% considering a global cropped area of
1411 Mha, would determine a sequestering of carbon of 7–110 GtC. The assumed
8.7 The Potential of Biochar in the Modulation …
303
(BLC) or in another way, the question of how much biochar soil can tolerate. Soils
with high biochar concentrations corresponding to about 40% of their soil organic
carbon were found in the Amazonian Basin. Furthermore, after hundreds or thousands of years, the productivity of these soils did not decrease or even increase. The
evidence available points out, for example, that in a weathered tropic soil, crop
yields kept increasing with biochar loadings up to 140 t Cha
−1 . On the other hand,
other trials showed that some crops delivered positive effects concerning biomass
and yields, at much lower applications. For example, experiments with bean
(Phaseolus vulgaris L.) cultivation showed positive yield effects with application
rates up to 50 t Cha
−1 , which disappeared with a rate of 60 t Cha
−1 , along with yield
decreases at application rates of 150 t Cha
−1 . This is indicative that BLC is likely to
be dependent on crops, on soil and climate, and on rates of application and total
accumulated amounts as well. Overall, it is likely that crops respond positively to
biochar additions up to 50 t Cha
−1 with possible growth reductions at very high
rates of application.
Smoldering combustion is another variable interfering with BLC, insofar that this
kind of combustion can be supported for years or long time periods in organic soils
that dry out sufficiently. Thus, soils with extreme loadings of biochar, subjected to
drastic drying conditions, could eventually withstand smoldering fires ignited by
natural or anthropogenic factors. This is an issue also requiring long-term research.
The sum of downward CO 2 from the atmosphere to the ocean, soil, and vegetation is of the order of 213.35 GtC, and the sum of upward fluxes to the atmosphere
of non-anthropogenic sources which were soil, vegetation, oceans, and forests
accounts for about 211.6 GtC, so that e.g. in 2004 a net loss of carbon from the
atmosphere was of around 1.75 GtC. This loss was however more than compensated
by anthropogenic sources of 5.5 GtC, delivering to a net gain of around 3.75 GtC, for
which a significant contribution for mitigation could be achieved through biochar
addition in soil. The hypothetical equilibrium of anthropogenic carbon emissions
should be thereby the main objective to achieve with biochar in soil (e.g., Verheijen
et al. 2010). As aforementioned, the carbon dioxide emissions were higher of around
9.9 GtC in 2017 and averaging 4.7 GtC in the period 2008–2017.
Also, global emissions of greenhouse gases were reported as increasing by 35%
from 1990 to 2010 reaching about 13.6 GtC. These later data ranges from 0.4 to 2.5
orders of magnitude from the value of 5.5 GtC of 2004, a variation which is not
incompatible with the hypothetical equilibrium role of compensation, already
mentioned, are attributed to biochar. Estimations were carried out indicating that
storing carbon in biochar would compensate global carbon yearly emissions of
about 0.1–0.3 Gt CO 2 .
Other projections mention that carbon sequestration of biochar, resulting from
forestry and agricultural residues and urban wastes, would reach by 2100 yearly
values ranging from 5.5 to 9.5 Gt C, values of the same order of magnitude of
current fossils fuel emissions. Also, an application of 10–100 Mgha
−1 of biochar,
with carbon concentration around 50–78% considering a global cropped area of
1411 Mha, would determine a sequestering of carbon of 7–110 GtC. The assumed
8.7 The Potential of Biochar in the Modulation …
303