Impacts of Land-use Change on Carbon Stocks and Dynamics in Central-southern South American Biomes: Cerrado, Atlantic Forest and Southern Grasslands - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 256

or biologically fixed nitrogen (consociation
with Stylosanthes guianiensis ) showed a gain
of 10.6-13.3 Mg C ha - 1 (0-100 cm), 3-4 years
after establishment. In contrast, soils with-
out nitrogen amendment, under Brachiaria
decumbens , showed early signs of degrad-
ation, and loss of 2.6 Mg C ha - 1 (0-100 cm)
(Silva et al ., 2004), in the same period. Cerra-
do biome topsoils (0-5 cm), with higher clay
contents, lost lower amounts of soil organic
carbon (19% in clay oxisols versus 48% in
sandy entisols) (Zinn et al ., 2002). In deeper
soil strata (0-60 cm), carbon losses were also
higher in sandy entisols under Eucalyptus
spp., while no net losses occurred in oxisols.
The influence of soil texture on the re-
sponse of carbon sequestration to sugarcane
harvest management is very significant, es-
pecially in traditional burning harvest sys-
tems, when impacts on soil carbon are
much higher. Burning sugarcane prior to
harvesting results in higher SCS losses than
unburned sugarcane areas, especially for
sandy soils (Resende et al ., 2006; Balieiro
et al ., 2008; Luca et al ., 2008; Galdos et al .,
2009). Eight years after replanting sugar-
cane at a site in the Atlantic Forest biome
(São Paulo), the unburned plots showed an
increase in total soil carbon at the 0-10 cm
layer of 41%, compared to the burned fields
(23.30 × 16.57 g C kg -1 ) (Galdos et al ., 2009).

reduction of greenhouse gases in the atmos-
phere calls for the implementation of agricul-
tural systems with lower carbon footprints.
This review has shown that improved soil
and crop management in agricultural sys-
tems can counteract most of the soil carbon
losses derived from LUC in the region.
Soil and crop integrated management
systems can partially reverse agricultural
soil carbon losses. The magnitude of these
losses and gains varies greatly with land-
use history, soil management, climate, soil
type and soil cover. In the Argentinian
Southern Grasslands, conventional agricul-
ture with annual crops led to an overall loss
of 34 Mg C ha - 1 (50% loss), considering the
last 100 years (Alvarez, 2001). In the Cerra-
do biome, conventional tillage was shown
to lose 33% of the SCS in one year (Jantalia
et al ., 2007). On the contrary, SCS could be
increased significantly in degraded Cerrado
biome pastureland converted to conserva-
tion agriculture systems, such as no-tillage
including nitrogen-fixing legumes in the
crop rotation scheme. Forestry can be bene-
ficial in the northern parts of the region,
where afforestation in the Cerrado and At-
lantic Forest biomes can result in soil car-
bon sequestration rates of 1.22 (Corazza
et al ., 1999) and 1.73 Mg C ha - 1 year - 1 (Mac-
edo et al ., 2008), respectively, the latter
with N 2 -ixing trees. However, in humid en-
vironments of the southern portion of the
basin, afforestation with eucalyptus or pine
monocultures has been shown to cause a
decrease in SCS.
The data presented show the import-
ance of no-tillage systems for soil carbon se-
questration and storage. It also reinforces the
need to maintain high levels of plant residue
inputs to the soil, so as to boost carbon se-
questration and stabilization in the soil, re-
ducing the agricultural carbon footprint in
all biomes studied. In the Cerrado biome,
soil carbon sequestrations up to 1.43 Mg C
ha - 1 year - 1 have been reported (Corazza et al .,
1999) and in the Southern Grasslands, a
nearly 26% increase in SCSs were obtained
by no-tillage systems compared to conven-
tional systems, 9 years after their establish-
ment (16.6 × 13.2 t C ha - 1 in NT × CT systems,
respectively) (Quiroga et al ., 2009).

Conclusions

To meet the increasing global demand for
food and bioenergy, the sharp increases de-
manded for agricultural production in rural
landscapes must be balanced with greater
environmental and social sustainability.
This review focused on the understanding
of the LUCs in the Cerrado, Atlantic Forest
and Southern Grasslands, major biomes in
central-southern South America, during the
past 40 years. Conversion of the native vege-
tation to agricultural systems was shown to
cause a significant reduction in SCSs, for all
biomes analysed. We suggest soil carbon
losses are derived mainly from lower C in-
puts to the soil under crop production, and
to a lesser extent to higher C outputs (respir-
ation) from the soil. The global need for a