Agriculture Reference
In-Depth Information
occur
13
years after reforestation using N
2
-
fixing legumes (
A. mangium
,
Acacia auric-
uliformis
,
Enterolobium contortisiliquum
,
Gliciridia sepium
,
Leucena leucocephala
,
Mimosa caesalpiniifolia
and
Paraseroanthes
falcataria
) to reclaim an area degraded by
gully erosion processes in the Atlantic Forest
biome (Macedo
et al
., 2008).
Results from ongoing studies in the La
Plata Basin Grasslands show that the forest
cover on soils originally formed under grass-
land strongly affects their chemical and
physical properties, significantly impacting
soil fertility, carbon stocks and hydrology
(Jobbagy and Jackson, 2003; Jobbágy
et al
.,
2006; Farley
et al
., 2008; Berthrong
et al
.,
2009a). Tree plantations are often regarded
as a global C sequestration option. However,
in the Southern Grasslands, the plantations set
off part of their biomass C gains with soil C
losses, particularly in grassland environments,
under humid climates and in first rotations
(Berthrong
et al
., 2009a,b, 2012). The extent of
SCS changes due to afforestation will depend
mainly on the age of the plantation and the
mean annual precipitation (Balieiro
et al
.,
2004, 2008; Resende
et al
., 2006; Berthrong
et al
., 2009a,b, 2012; Eclesia, 2011)
(Fig. 21.6)
.
Afforestation usually increases SCSs in
dry areas and decreases them in humid en-
vironments, depending on the stand age. In
specific cases, where afforestation is used to
recover degraded agricultural soils, increases
in soil C stocks have been observed, depend-
ing on the forest species, the presence of
mycorrhiza, whether they are grown in con-
sortia with legumes and the soil type (Riestra
et al
., 2012).
LUC is affecting the albedo (surface reflect-
ance) of large areas in the region significantly
(Lee and Berbery, 2012). Albedo changes after
afforestation are a direct climate effect that
offsets that of C storage on climate. The impact
of albedo changes becomes more relevant to-
wards temperate and drier zones. Other un-
wanted side effects of afforestation in the
Southern Grasslands are high water consump-
tion, soil cation depletion and biodiversity
losses (Farley
et al
., 2008; Jackson
et al
., 2008).
Land Use, Crop Management and Soil
Organic Carbon Sequestration
Several researchers have argued that SCSs
in the Cerrado biome could be improved if
good agricultural practices were adopted
(Corazza
et al
., 1999; Bayer
et al
., 2006;
Bustamante
et al
., 2006; Jantalia
et al
., 2007;
Carvalho
et al
., 2010a). Systems under NT,
crop rotation or consociation with nitrogen-
fixing legume species show the highest car-
bon sequestration potentials, with a special
emphasis on crop-livestock, or crop-livestock-
forestry integrated systems (Sisti
et al
., 2004;
Bayer
et al
., 2006; Bustamante
et al
., 2006;
Corbeels
et al
., 2006; Jantalia
et al
., 2007;
Batlle-Bayer
et al
., 2010; Carvalho
et al
.,
2010b). The positive effects of NT on SCSs can
be observed after a period of organic matter
(a)
150
150
(b)
600 mm
1000 mm
1400 mm
1800 mm
2200 mm
100
100
2600 mm
2200 mm
1800 mm
1400 mm
50
50
0
0
-
50
-
50
0
0
0
0
0
100
0
2
0
0
0
0
100
-
100
-
100
Plantation age (years)
Pasture age (years)
Fig. 21.6.
Multiple regression model between the effect of age since conversion to (a) tree plantations
and to (b) pasture, and changes in SOC contents at different levels of mean annual precipitation (MAP).
The arrows indicate the direction of increasing MAP isohyets. (From Eclesia, 2011.)
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