Climate Change Mitigation - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 123

This finding has important implications for
the potential and means of capturing syner-
gies between mitigation and food security
( Branca et al ., 2013a).
Since the IPCC (2007) assessment, new
practices have been considered, including
the use of biochar as a soil amendment and
also the application of 'chipped ramial
wood' to cultivated fields.
Biochar is produced from pyrolysis of
biomass heated between 300°C and up to
1000°C under zero (or extremely low) oxygen
concentration. Biochar is considered to be
constituted mostly of recalcitrant or stable
organic C, and has been proposed as a miti-
gation solution that also improves soil prop-
erties and functionality. A recent report
(Verheijen et al ., 2010) concluded that the
carbon sequestration potential of biochar
was largely hypothesized and important un-
certainties remained, particularly regarding
the effects on CH 4 and N 2 O fluxes. Biochar
applications have also been found to im-
prove the overall soil quality and increase
yields. Jeferry et al . (2011) reported, in a
quantitative review of the effect of biochar
on crop productivity, a mean yield increase
of 10%, although with a wide range in yield

responses, from −28% to +39%. The highest
increases were observed for acidic and neu-
tral pH soils and medium- to coarse-texture
soils. The efficacy of biochar for GHG miti-
gation is currently under debate, and there
are still large unknowns and potential risks
that need to be quantified.
Chipped ramial wood (CRW) consists
of the twigs and branches of trees or shrubs
used in cultivated land for mulching. Ori-
ginally a by-product of hardwood logging
and processing in Canada, some scientists,
farmers and non-governmental organiza-
tions (NGOs) have advocated the use of
CRW to improve soil fertility and rehabili-
tate degraded soils. With a high content of
cellulose and lignin, CRM is considered to
stimulate soil fungi. As is typically the case
with new cultivation practices - to date, more
attention has been paid by farmers, NGOs
and extension services - scientific investi-
gations are scarce. Barthès et al . (2010) per-
formed a synthesis of available experimental
results and concluded that CRW had a posi-
tive effect on crop yield (except for the first
year in some cases), increased soil organic
matter (and thus SOC) and improved medium-
term nutrient availability (Fig. 9.1 ) . However,

200 200

(a) Temperate region

(b) Tr opical region

150 150

100 100

50 50

0 0

100 100

0 50 150 200 250 300

To tal input of ramial wood (t DM ha -1 )

0 50 150 200 250

Fig. 9.1. Impact of the addition of chipped ramial wood (CRW, expressed in cumulative quantity in
dry matter (DM) per hectare) on soil organic carbon in relation to a control without CRW. White symbols
correspond to situation without additional inputs, black symbols to situation with CRW plus additional
inputs. The same symbols correspond to different measurements during the experimentation.
(From Barthès et al ., 2010.)