Principles of Soil Management in Neotropical Savannas - Principles of Sustainable Soil Management in Agroecosystems - page 61

et al. 1986). These altitudes, combined with the inland continental location ( Figure
3.1 ), increase solar radiation and decrease the amount of precipitation coming from
the ocean. In comparison, the Llanos is much lower (mostly between 50 and 300 m
a.s.l.) and closer to the Atlantic Ocean, resulting in higher precipitations. However,
topography can be roughly considered as a long-term response of geological struc-
tures to erosion, and thus, there are other direct effects of it on soils. As mentioned
earlier, most rocks in the Cerrado are extremely old, and although some sparse tec-
tonic uplift has occurred in the Pliocene (2.6-5.3 M years B.P.), most land elevations
are much older (Saadi et al. 2005). Therefore, there are few recent mountain ranges,
and thus, Cerrado landscapes basically consist of erosional surfaces, which are very
large, roughly level areas resembling a plateau from a distance, where streams and
drainageways carve typically gentle slopes (<10%) and reliefs (<100 m). An older
erosional surface always occupies a higher altitude than a younger one, and their
transition is apparent in the field (Figure 3.2). In the Cerrado, the main erosional
surfaces are the Gondwana (remnants of rocks denuded during the existence of the
supercontinent formed by South America and Africa, >145 M years B.P.), the South
American (the dominant surface, with rocks denuded during the late Cretaceous
100-65 M years B.P.), Velhas River (Miocene-Pliocene, 2.6-23 M years B.P.),
and Paraguassu River (Quaternary, <2 M years B.P.), according to Thomas (1994)
and Marques et al. (2004). Although it is important to understand the formation of
FIGURE 3.2 Smooth landscape (Sul-Americana erosion surface) most commonly associ-
ated to Oxisols, between the cities of Brasília and Goiânia. A well-managed pasture is shown
in the first place, and a riverine (“gallery”) forest is seen as a thin tree strip along the drain-
ageway a few hundred meters away. In the distance is the Pireneus quartzite range (a remnant
of the Gondwana erosion surface), where soils are too poor and sandy for cropping.