Principles of Soil Management in Neotropical Savannas - Principles of Sustainable Soil Management in Agroecosystems - page 69

much more exchangeable bases than other Ustoxes (Zinn et al. 2007a; Zinn and
Resck 2008). Thus, since 2000, more and more of these fertile plinthic soils of the
Cerrado are being cultivated for rice ( Oryza sativa ) paddy fields, but also for soybean
following artificial drainage (Oliveira, G.C., personal communication).
Inceptisols cover ~3% of the Cerrado area (Adámoli et al. 1986), mostly on the
steep borders of plateaus or hilly lands, where they are often associated with Ustoxes
(summit) and Ustults (less pronounced slopes). Most of these soils are classified as
Dystrustepts, derived from preweathered rocks and thus are acidic and low in basic
cations. Haplustepts are also common and may have higher fertility when developed
from basalt or limestone. Bulk density of these soils is similar to those of Ultisols,
ranging from a mean 1.07 Mg m -3 in the surface to 1.35 Mg m -3 to 1-m depth (Araujo,
M.A. et al. 2011). Crop productivity is limited by low or extremely low fertility, shal-
low rooting depth, steep slopes, and vulnerability to interrill or sheet erosion. Thus,
these soils are most commonly used for pastures, forest plantations, and perennial
crops. However, high doses of gypsum (>10 Mg ha -1 ) can greatly enhance depth of root
penetration of coffee in Ustepts in southwestern Minas Gerais (Serafim et al. 2011).
Entisols with lithic properties occupy ~7.3% of the Cerrado (Adámoli et al. 1986)
and commonly occur on quartzite ranges, steep slopes, or recently exposed rock sur-
faces. In Brazil, these soils are named Neossolos Litólicos , and low or extremely low
fertility and water retention are among principal constraints to agronomic productiv-
ity. Thus, these soils are commonly used for extensive grazing. However, many low-
income farmers depend on these and other unproductive soils to grow annual and
perennial crops, especially cassava ( Manihot esculenta Crantz).
Soils with aquic moisture regimes and without plinthite occupy about 2% of
Cerrado (Adámoli et al. 1986). While more commonly confined to drainageways and
lowlands, they sometimes occur in uplands where perched water tables accumulate
over impervious layers. Some of these soils can accumulate deep peat and/or high
SOC stock because of slow rates of organic matter decomposition under anoxic con-
ditions. However, this C accumulation can be readily lost upon artificial drainage or
by drastic lowering of water tables during the dry season, even causing subsoil fires.
In the Brazilian System, these soils are included in the separate orders Gleissolos
and Organossolos , the latter being equivalent to Histosols. Many small landholders
cultivate these soils for growing horticultural crops or vegetable gardens, because
of abundance of water and relatively high fertility. Rice paddy, although a common
land use in Southern Brazil, is not common in aquic soils of the Cerrado.
3.2 PRINCIPAL LAND USE AND SOIL MANAGEMENT
SYSTEMS IN THE CERRADO
By the year 2002, approximately 40% of the total Cerrado biome, (or ~80 M ha) had
been converted to some kind of anthropogenic use (Sano et al. 2010). This land con-
version has been mostly concentrated near the densely populated Brazilian south-
east, on the southern reaches of the Cerrado biome ( Figure 3.1 ), where ~85% of
the land surface has been reclaimed, in contrast to only 10% in the northernmost
regions. Thus, the Cerrado underwent a rapid land settlement leading to an immense