Agriculture Reference
In-Depth Information
average livestock carrying capacity from 0.3 to 1.0 AU/ha (Machedo 1997). It has
been estimated that some 85% of pastures in the cerrado are Brachiaria (Landers
2007).
Brachiaria has a deep, well-developed root system that can penetrate depths of
more than 1 m, with at least 20% of the total root system present below 0.30 m.
Intercropping increases soil aggregation and stability of aggregates, lessens bulk
density, and increases macroporosity and water infiltration.
The total dry biomass of a Brachiaria root system can reach 1.7 t ha -1 . This fact is
important for cycling nutrients like potassium, magnesium, sulfur, and nitrogen that
are subject to leaching in tropical agriculture soils. The Brachiaria mulch decreases
the soil temperature, keeping the soil environment cool and wet, thus increasing
soil biological activity. Therefore, the intercrop system is very efficient in nutrient
cycling and reducing nutrient losses by runoff and leaching.
This intercrop system can sequester soil carbon in the range of 0.5 to 1.0 t C ha -1
year -1 . These rates are double those for regular no-till carbon sequestration with
systems that have only a tillage change with grain crops held constant. The soil loss
then reduced to the range of 0 to 3 t ha -1 year -1 , which is around three times lower
than other no-till grain systems, and it is in equilibrium with soil formation.
The large amount of aboveground Brachiaria biomass is important to reduce
weed infestation, especially with Conyza bonariensis, Commelina benghalensis,
Euphorbia heterophyla , and Cenchurs echinatus. Weed infestations are one of the
most serious threats to continuous no-till in the tropics. The total weed reduction
provided by Brachiaria generally is in the range of 30% to 70%.
Brachiaria can suppress important diseases of soybean and black beans such as
Fusarium solani infestation by approximately 60%. Also, Rhizoctonia solani can
be reduced by Brachiaria intercropped with grain crop production. One of the most
common pathogens in the South American tropics is Sclerotinia sclerotiorum , and
the combination of a grain crop with Brachiaria is one of the best options to reduce
this disease. Intercropped Brachiaria and maize provides competitive maize yields
and forage to cattle during an otherwise fallow period, providing income diversifica-
tion. This system is an important option to sustain no-till for the long term in tropi-
cal environments. It has restored degraded pastureland and degraded forestland in
Central Brazil.
14.6.3 c roP -l iveStock i integration for S uStainaBle S oil m anagement
Pastureland has important ecological functions. It often contains a high percentage of
perennial grasses, which have the ability to sequester and safely store high amounts
of carbon in the soil at rates that exceed by far those of annual crops. This capac-
ity can be enhanced with appropriate management, for example, replacing exported
nutrients, maintaining diversity in plant species, and allowing for sufficient recovery
periods between use by grazing or cutting. In conventional farming systems, there is
a clear distinction between arable crops and, mostly permanent, pastureland. Under
CA-based farming, this distinction does not exist anymore, since annual crops may
rotate into pasture and vice versa without the destructive intervention of soil tillage;
it is just as additional element of cropping diversity.
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