Managing Soil Carbon for Multiple Ecosystem Benefits – Positive Exemplars: Latin America (Brazil and Argentina) - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 279

verified higher aromatic group concentra-
tion of humic acids in the superficial layer
(0-10 cm depth) of older areas, while in the
subsuperficial layer ( 10- 20 cm depth), there
was no difference due to time of system
adoption.
About 50% of total sugarcane in Brazil
(approximately 4 Mha) is still burnt prior
to harvest (Canasat, 2011). Once those
areas are converted from burning to mech-
anized harvest, a huge amount of crop resi-
due is left on the soil surface, in some
places close to 15 t ha - 1 , which is equiva-
lent to 6 t of C. Several studies have been
conducted on sugarcane areas converted
from burned to green harvest and have
shown an important enhancement of soil
carbon stocks due to this conversion (Cerri
et al ., 2011). The increases in soil carbon
stocks reported in these field studies, at
least in the first years of green harvest adop-
tion, would be enough to compensate for
all emissions associated with other agri-
cultural practices. Recent estimations of
the amount of GHGs emitted to the atmos-
phere associated with all sources in the
agricultural management of sugarcane
fields in southern Brazil mention about 3 t
CO 2 equivalents ha - 1 year - 1 (De Figueiredo
and La Scala, 2011). A soil carbon accumu-
lation rate of 1 t ha - 1 year - 1 , which has been
observed in many field studies (Cerri et al .,
2011; La Scala et al ., 2012), would be
enough to compensate for the emissions
associated with crop production, and the
ethanol derived from this agricultural man-
agement would have close to a 'zero emis-
sion' footprint.
Renovation operations with intensive
soil tillage promote mineralization of SOM
(Silva-Olaya et al ., 2013) and attenuate dif-
ferences between burning and no-burning
harvest systems (Resende et al ., 2006). To
understand better the carbon balance and
the system potential to increase C stocks in
no-burning sugarcane areas, it is important
to take into account the tillage system dur-
ing the renovation period (De Figueiredo
and La Scala, 2011). La Scala et al . (2006)
evaluated the effects of conventional till-
age (mouldboard ploughing followed by
two passes of offset disk harrows), reduced

tillage (chisel ploughing) and no-till on
CO 2 emissions from sugarcane soils. The
CO 2 emissions during 1 month after soil
tillage were increased by 160%, and by
71% when soils were prepared with con-
ventional and reduced tillage as compared
to no-till, respectively. The results suggest
that in a 1- month period after tillage, 30%
of soil carbon input in sugarcane crop res-
idues could be lost after ploughing tropical
soils, when compared to the no-till plot
emissions.
The same set of studies has also
pointed to another important aspect: once
the sugarcane fields are reformed and till-
age is applied, a large amount of CO 2 is
emitted from soil, and soil carbon stocks
are depleted dramatically (Cerri et al .,
2011). Hence, the adoption of green har-
vest in sugarcane fields, with the input of
large amounts of residues on soil surface
should, desirably, be combined with a re-
duced or even no-till practice. This would
be an ideal production scenario, a win-
win situation where less fossil fuel and
synthetic fertilizer use would result in
higher soil carbon stocks.
In addition to reducing the depend-
ence on fossil fuels, another objective of
ethanol use is to mitigate GHG emissions
(Cerri et al ., 2007; Goldemberg et al ., 2008).
Brazilian sugarcane ethanol presents a
mean decrease of 85% in GHG emissions
compared to fossil fuels, while American
maize ethanol presents a reduction of only
25% (Börjesson, 2009). Galdos et al . (2010)
presented data for Brazilian ethanol pro-
duction showing that most ethanol GHG
emissions occurred in the field during sug-
arcane production. De Figueiredo et al .
(2010) quantified the carbon footprint of
sugar production in two Brazilian mills and
observed that 241 kg of CO 2 equivalent
were emitted to produce 1 t of sugar, 44%
of this from burning, 20% due to mineral
fertilizer use and about 18% derived from
fossil fuel combustion, confirming the in-
formation reported by Galdos et al . (2010).
Brazilian ethanol has another advantage:
a lower production cost per litre in relation
to fossil fuel extraction and refinement (Luo
et al ., 2009).