Principles of Soil Management in Neotropical Savannas - Principles of Sustainable Soil Management in Agroecosystems - page 79

plantations are generally large and established on Haplustoxes and Haplustults of low
to moderate relief. Typically, sugarcane is planted as stem cuttings with buds, which
are inserted by hand or mechanically along planting rows, usually following site
preparation with plow and harrow, or only heavy harrow. Harvest takes place annu-
ally and is still mostly done by hand and machete after burning, although mechanical
harvesting is gradually increasing. Fertilizer use is generally less than 100 kg N ha -1
year -1 , and it has been estimated that biological N fixation supplies ~60% of crop
demands (Lisboa et al. 2011).
Since sugarcane is a perennial crop commonly lasting six annual cycles, soil does
not need to be disturbed annually, yet soil degradation and erosion under sugarcane
plantations is widespread, especially in coarse-textured soils and where harvest is
preceded by burning. Cerri et al. (2011) estimated that conversion from burned to
unburned plantations can sequester on average 0.7 and 2.0 Mg SOC ha -1 year -1 for
sandy and clayey Oxisols, respectively. Although sugarcane ethanol is one of the
cleanest biofuels, N 2 O emissions from N fertilization and C losses from conversion
of native vegetation to sugarcane may offset CO 2 mitigation from petrol substitu-
tion (Lisboa et al. 2011). The emission of other air pollutants is also significant and
probably underestimated, even where burning is being abandoned (Tsao et al. 2011).
Despite the availability of technologies for the use of sugarcane residues (bagasse
and vinasse), its potential for energy generation is still largely untapped and the dis-
posal of these materials is a major concern.
3.2.7 C rop /l iveStoCk i ntegrationS
Crop/livestock integrations are innovative land use systems based on millennia-old
practices, in which crops and pastures are alternated on the same land, aiming at a
combination of management practices and effects on soil properties that eventually
enhance soil quality, productivity, and biological diversity. There is large global vari-
ability on how this system is used, and in the Cerrado, it commonly involves three
major options (Vilela et al. 2008): (1) pasture-based farms that plant crops in order
to enhance productivity by reducing liming and fertilization costs with the income
from grains; (2) crop-based farms that plant forage grasses in the dry season aiming
to increase mulching for NT crops (especially maize and Sorghum ); and (3) farms
that systematically do crop/pasture rotations in all or most areas.
Despite the variability of these systems and the relatively recent onset of system-
atic studies on the theme, there exists research evidence that crop/livestock integra-
tions may enhance soil quality in the Cerrado. In a 13-year-long experiment near
Brasília, Marchão et al. (2007) reported increased bulk density and reduced macro-
pore volume in comparison to the native Cerrado vegetation. Although the compac-
tion was statistically significant, the magnitude of changes was too small to raise
any concern. In the Cerrado of Mato Grosso do Sul, Salton et al. (2011) reported
that SOC sequestration rates in soybean/livestock rotations were about half of those
under continuous Brachiaria pastures (~1 Mg ha -1 year -1 ), whereas NT and conven-
tional till plots showed no SOC changes even after 10 years. Additional research is
needed to address a wider range of combinations of crop and grazing species, and
management practices.