Agriculture Reference
In-Depth Information
3.2.3 a
nnual
C
ropS
Croplands are the second most important land use in the Cerrado biome and cov-
ered 21.6 M ha by 2002 (Sano et al. 2010). While these statistics do not differentiate
between annual and perennial crops, croplands are primarily concentrated in the
most developed southern and western areas of the Cerrado. Unlike pastures, produc-
tive annual crops are mainly planted on clayey, but also on coarser Ustoxes, as well
as on Quartzipsamments and Ustults when slopes are not too steep. Although occu-
pying less than half the area under pastures, croplands pose a higher environmental
impact because of their intensive management and often with heavy use of pesticides,
fertilizers, and mechanization. However, as mentioned earlier, this was not always
the case, since early farmers in the Cerrado only grew rice or corn immediately fol-
lowing the land clearance, with little or no inputs, obtaining low productivities for no
more than 2 years. At present, after decades of government incentives and research
and development, cultivations of annual crops in the Cerrado have become highly
technical and productive, most commonly involving soybeans and corn, but also
rice, beans, and more recently, cotton. Liming and fertilizer use have also become
more widespread, and in fact, some farmers are applying doses much above the tech-
nically recommended rates, aiming to build “nutrient banks,” especially of P, which
may result in losses but also increase overall soil quality. Even when initial P levels
were adequate, annual rates of fertilizer use of 100 kg P ha
-1
for 11 years to corn/
soybean rotations caused small but significant increases in SOC stocks for a 0- to
20-cm depth (Nunes et al. 2011).
Conventional tillage for annual crops in the Cerrado traditionally involves disk
plowing and harrowing prior to planting, and in some cases, crop residues are
incorporated right after harvesting. Moldboard plowing is less common than disk
plowing, whereas a heavy disk harrowing is frequently used instead of plowing and
harrowing. When applied to a typical clayey Haplustox of high macroporosity, these
implements adversely impact bulk density, saturated conductivity, and compressive
behavior in the order of moldboard plow>disk plow>heavy disk harrow (Silva et al.
2003). However, over a long period, these tools cause different effects depending on
the crop and soil type. Continuous (>15 years) use of disk plow for a soybean/corn
rotation in a clayey Haplustox strongly decreased the proportion of macro (>2 mm)
water-stable aggregates from 80% under native Cerrado to only 15%, whereas the
heavy harrow was less disruptive, maintaining ~50% of large macroaggregates
(Resck et al. 2001).
Whatever the implement, annual tillage operations demanded large amounts
of fuel and time of farmers and became expensive in increasingly larger farms.
Additionally, widespread soil compaction and erosion resulting from annual tillage
encouraged the Cerrado farmers to no-till (NT) systems, which had been used in
Paraná, southern Brazil, since the 1970s. The rapid and wide adoption of NT for
annual crops is perhaps the most striking shift in soil management systems that ever
happened in Brazil and in the Cerrado. Presently, NT systems are almost univer-
sally used for large-scale annual crops in the Cerrado, and annual tillage is all but
restricted to small areas in family farms. In consequence of the NT boom, the use of
herbicides and pesticides has drastically increased.
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