Principles of Soil Management in Neotropical Savannas - Principles of Sustainable Soil Management in Agroecosystems - page 78

through genetic breeding and, in the case of insect pests, with biological control by
natural enemies introduced or preexistent in nearby areas under native vegetation.
As for pastures, soil management in plantation forests is sparse and of little inten-
sity when compared to croplands, but it still affects soil properties depending on soil
type and site preparation. Planting E. camaldulensis Dehnh. using heavy harrow on
the whole area resulted in lower SOC concentrations at the 0- to 5-cm depth by the
age of 7 years, and more intensely on sandy than on loamy Haplustoxes in the central
Cerrado region (Zinn et al. 2002). However, after the stands were cut and allowed to
sprout as coppice stands without further site preparation for 7 more years, SOC was
resequestered and no significant differences in SOC stocks occurred in comparison
to the native vegetation (Zinn et al. 2011). On the other hand, when Eucalyptus trees
were planted without an intensive site preparation, SOC stocks at age 16 years were
similar or even larger than those under native Cerrado (Resck et al. 2000). Thus,
synthesis and analysis of a large number of published reports show no significant
difference between SOC stocks under Eucalyptus plantations and native vegetations
in Brazil as a whole and in the Cerrado region (Fialho and Zinn 2012). Pinus planta-
tions are much less studied, but it is known that the slow decomposition of its needle
layers favors wildfires and tends to result in lower surface SOC levels (Zinn et al.
2002).
Soil physical properties are also affected by afforestation, depending on site prep-
aration. Zinn et al. (2011) observed that mean aggregate size under Eucalyptus was
always smaller than that under native vegetation, suggesting that soil aggregation
recovers more slowly than SOC when disturbance is interrupted. Soil compaction
following the use of heavy harvesters, feller bunchers, and skidders to extract wood
has been reported elsewhere in Brazil, but not yet in the Cerrado region, where these
machines are less common and few or no studies have been conducted.
3.2.6 B iofuel C ropS
Brazil is well known for having perhaps the most successful industry of first-
generation biofuels, based on the production of ethanol from sugarcane ( Saccharum
spp.), used as single fuel or mixed with gasoline for most modern Brazilian cars,
which run with both fuels (i.e., “flex” cars). With regards to agricultural and industrial
initiatives in Brazil, the success of biofuels is attributed to large public investments
on research and technology and intervention on markets (Moraes 2011), mandated
after the petroleum crisis of 1973. Recent efforts have also focused on plant-derived
oils, which federal law mandates to be mixed with diesel at a 2% rate (“biodiesel”)
for use by trucks. Although crops such as sunflower ( Helianthus annuus L.) and oth-
ers are currently spreading in the Cerrado and other regions to meet this demand,
such efforts are at a much lesser scale and profitability than for sugarcane ethanol,
which is the focus of this section.
Sugarcane is an important biofuel crop in the world, and Brazil is its major pro-
ducer, especially along the Atlantic coast and in the State of São Paulo, where it is
often planted on former Cerrado land. Currently, sugarcane plantations are spread-
ing through many Cerrado areas where they have never been planted before, such
as in Goiás, due to high demand not only for ethanol but also for sugar. Sugarcane