Principles of Soil Management in Neotropical Savannas - Principles of Sustainable Soil Management in Agroecosystems - page 68

has a very different classification approach to these soils and recognizes the separate
order Plintossolo , in which suborders are defined based on the presence of clay illu-
viation and ironstone layers or gravels (Embrapa 2006). The nomenclature used in
the study of these soils is variable: ironstone and plinthite are commonly termed “lat-
erite” across disciplines other than Soil Science, and soils rich in these materials are
named “Latosols” by Padmanabhan and Eswaran (2002), a term also used by many
Brazilian soil scientists as a translation for Latossolos (Oxisols). Basically, these
soils present significant Fe concentrations and cementations where oxic and anoxic
conditions alternate, or where relict materials thus indurated are being exposed or
dismantled, often on steep borders of plateaus. Ironstone remnants can thus be dis-
tributed throughout the landscape and appear as opaque sands or gravels ( Figures
3.3 and 3.4) in almost all types of Cerrado soils. Plinthite-forming conditions exist
in many but not all lowlands and drainageways and appear to be rarer where organic
soils and peats occur (Skorupa et al., in press). Plinthic soils are commonly derived
from Fe-rich parent materials such as clayey sediments, basalts, and especially ultra-
mafic rocks (Trescases et al. 1979), but they can form from low-Fe rocks such as
quartzites in small areas where Fe-enriched water flows from uplands for a long
time. Thus, the principal limitations to intensive use of these soils are poor drainage,
year-round waterlogging, and heavy wear-and-tear of plows and other soil prepara-
tion tools. In addition, many of these soils occur on steep slopes, and most are acidic
and nutrient-poor. However, about 10% of plinthic soils have high nutrient levels
(Adámoli et al. 1985), either due to nutrient flow from uplands or to strong micro-
nutrient sorption by the Fe-oxides. Some of these fertile plinthic soils are unexpect-
edly young and contain significant amounts of weatherable minerals, as observed
in a Plintaquult in the Cerrado of Goiás (Moreira and Oliveira 2008). Some upland
clayey Ustoxes of the Cerrado, with ironstone gravel contents too low to have a plin-
thic diagnostic horizon, present lower internal drainage and thus are able to retain
FIGURE 3.4 Scanned image of soil thin sections of a clayey Haplustox (0- to 5-cm depth)
cultivated with annual crops for 20 years under different soil preparation practices. From left
to right: native Cerrado vegetation, no-till, chisel plow, disk plow, and moldboard plow. Each
image is 2.7 cm wide. (Adapted from Skorupa, A.L.A. et al. Micromorfologia de um latossolo
do cerrado sob diferentes sistemas de manejo e preparo por vinte anos. In XXXIII Cong.
Bras. Ci. Solo. Proceedings . Uberlândia, SBCS, 2011. With permission.)