Principles of Soil Management in Neotropical Savannas - Principles of Sustainable Soil Management in Agroecosystems - page 76

lower than ammonium forms (Frazão et al. 2010) and most soils are so deep that nitrate
percolation may not reach groundwater. Nevertheless, additional research is needed to
enhance scientific understanding on these subjects.
3.2.4 p erennial C ropS
By definition, perennial crops have production cycles spanning many years, and thus
site preparation and tillage are used more infrequently than in annual crops, some-
times on intervals of 15 years or more. Thus, perennial crops generally cause less
impact on properties of Cerrado soil than do annual crops. The principal perennial
crops in the Cerrado are coffee ( Coffea spp.), cassava ( Manihot spp.), rubber trees
( Hevea spp.), and a range of fruit trees (sugarcane is discussed separately in Section
3.2.6). Soil management in fruit orchards is highly variable depending on the spe-
cies and farm size, and the management of rubber tree plantations, except for the
annual harvesting, is similar to that of planted forests (see Section 3.2.5). Although
cassava plantations are common in other regions of Brazil, cassava in the Cerrado
is typically planted in small farms or collective settlements, with little fertilizer or
other inputs, and soil preparation is often done with manual- or animal-drawn imple-
ments. Therefore, this section focuses on coffee plantations, by far the most promi-
nent perennial crop either in commercial value or in the planted area.
Productive coffee plantations are among the most intensively managed land use
systems in Brazil and usually employ large amounts of fertilizers, pesticides, and
labor throughout the year. Approximately half of the coffee production in Brazil
comes from the Cerrado region (Resck et al. 2008). Further, coffee is only planted in
the most fertile soils, although innovative management systems are currently being
developed that enhance productivity even in low-fertility Cerrado soils (Serafim
et al. 2011). Soil preparation before planting primarily involves liming, plowing, and
harrowing, as well as pitting for the seedlings, but these operations typically are
done every 15 to 30 years, when the stands are cleared and replanted. Although this
long rotation cycle may suggest that soil disturbance is low in coffee stands, in many
cases, soil tillage with harrowing is used for weed control between the planting rows.
In addition, heavy tanks with fertilizers and pesticides are pulled by tractors several
times per year, not to mention harvest machines used on a yearly basis. Therefore,
soil compaction and aggregate disruption are common in Haplustoxes and other soils
with low bulk densities under coffee plantations. In a clayey Oxisol under coffee for
>20 years in southern Minas Gerais, the relative volume of pores >50 μm decreased
by 25%-60% at a 0- to 3-cm depth depending on weed control systems and by ~30%
at a 10- to 13-cm depth, in comparison to soils under native dry forest (Araujo Jr. et al.
2011). However, in most cases, this compaction does not hinder coffee productivity,
and if this occurs, the stands are cut and the soil tilled again for a new plantation.
When the coffee plants are spaced densely (2000-3000 plants ha -1 ), biomass produc-
tion by the crop and weeds is significant and SOC levels may be preserved depending
on weed control systems. At the same site mentioned above, SOC stocks to a 0- to
30-cm depth (after correction for soil compaction) were similar to those under native
forest in plots where weeds were allowed to grow or controlled by mowing (Cogo et
al., in press). However, SOC stocks decreased by ~20% when weeds were controlled