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Intercropping
is considered as the practical application of ecological principles such
as diversity, crop interaction and other natural regulation mechanisms. Intercropping
is defined as the growth of two or more crops in proximity in the same
field during a growing season to promote interaction between them.
Available growth resources,
such as light, water and nutrients are more completely absorbed and
converted to crop biomass by the intercrop as a result of differences in
competitive ability for growth factors between intercrop components. The
more efficient utilization of growth resources leads to yield advantages
and increased stability compared to sole cropping.
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Furthermore,
the
multifunctional profile of intercropping allows it to play many other
roles in the agroecosystem, such as resilience to perturbations,
protection of plants of individual crop species from their host-specific
predators and disease organisms, greater competition towards weeds,
improved product quality and reduced negative impact of arable crops on
the environment.
Nitrogen
fixing legumes can be included to a greater extent in arable cropping
systems via intercrops. Legumes contribute to maintaining the soil
fertility via nitrogen fixation, which is increased in intercrops due to
the more competitive character of the cereal for soil inorganic N. This
leads to a complementary and more efficient use of N sources.
Intercropping of grain legumes and cereals therefore offers an
opportunity to increase the input of fixed nitrogen into agroecosystems
without compromising cereal N use, yield level and stability.
Despite
all its advantages, the agricultural intensification in terms of plant
breeding, mechanisation, fertiliser and pesticide use experienced during
the last 50 years has lead intercropping to disappear from many farming
systems.
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Methodology in
intercropping
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The
agronomic advantages of intercropping are the result of
differences in competitive ability for growth factors between intercropped
components. In terms of competition, this means that the components are
not competing for the same ecological niches and that interspecific
competition is weaker than intraspecific competition for a given factor.
The fact that the crops involved may have different resource
requirements as well as different growth patterns makes it more
complicated to define a proper methodology for the study of intercrops compared
to studies involving one species – sole cropping.
The
interpretation of interactive effects between intercrop components
activities and soil processes is extremely complex. For example,
specific crop growth affects soil shading and light interception and
therefore also temperature, plant water uptake changes soil water
content in the rhizosphere which effects microbial decomposition rates,
decomposition rates affect soil texture, water retention characteristics,
rooting profiles and nutrient availability to the crops. Experimentally
it is very difficult to disentangle these processes. Thus, to really
interpret all these processes at once and under variable and interacting
conditions, dynamic simulation models of these systems are valuable.
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Extent
of intercropping in Europe and worldwide
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Intercropping
was a common practice in Europe before mechanisation, plant breeding and
use of synthetic fertilizers and pesticides was implemented in a more intensified the agricultural
production starting in the 1950ties. Intercrops of clover and grasses in
pastures are still widely used in European agriculture, but arable
intercropping (cereals, grain legumes, oil seeds) for feed and human
consumption is presently not so common.
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It
has been scheduled that the entire animal feed sources in organic
farming should be of organic origin from 2005 in the EU (EU Commission
(EC) No. 1804/1999). This will require a major increase in organic
cereal and grain legume (protein) crop production, to balance the
European organic deficits. As an example, the French deficit for organic
feed protein, considering complete organic feed supply, was 9000 tonnes
in 1999.
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Re-introducing
intercropping in European organic agriculture to a greater extent should
not be reversion to old methodology, but rather considering the
usefulness of this old and sustainable cropping practice in a modern,
innovative and technology-oriented organic agriculture. Furthermore,
intercropping constitutes a concrete means to increase the
diversification of agricultural ecosystems, for which there is a
worldwide appeal.
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Agrobiodiversity
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The importance of
agrobiodiversity encompasses socio-cultural, economic and environmental elements.
All domesticated crops and animals result from human management of biological
diversity, which is constantly responding to new challenges to maintain and
increase productivity. Biodiversity provides not only food and income but also
raw materials for clothing and medicines, among others. It also
performs other services such as maintenance of soil fertility and biota, and
soil and water conservation, all of which are essential to human survival.
There is a growing awareness that the variety
of landscapes and the related biodiversity shaped by agriculture over centuries
could be harmed by the continued intensification. Intercropping is planned
biodiversity, and it is thought that planned diversification will increase
associated biodiversity, and in this way contribute to conserving biodiversity
in the open agricultural land and associated ecosystems.
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Organic farming
and intercropping
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Organic
farming is a steadily increasing production form in European agriculture.
It is environmental friendly, due to low input of nutrients and no use of
pesticides, and it contributes to the production of food without
pesticides and antibiotic residues. A further expansion of organic farming
is needed to meet consumers worldwide having an increasing demand for
products, which are healthy, safe, and of high quality and produced with
consideration for animal welfare and the environment. European organic
farming and research within this area are in the forefront internationally
and offers the opportunity of a food production, which could strengthen
the competitiveness of EU agriculture.
Intercropping
is of special relevance and importance in future organic farming systems,
because it offers a number of significant enhancements of both the net
productivity of organic farming and the ecosystems in farming regions as a
result of the increased diversity of the cropping system.
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Intercropping
is a method for simultaneous crop production and soil fertility building and
it may also contribute to the prevention of nitrogen leaching risks
sometimes observed from sole crops such as grain legumes due
to changes in incorporated residue chemical quality involving nutrient
turnover. It is also an ecological
method to manage pests, diseases and weeds via natural competitive principles
that allow for a more efficient resource utilisation. This same competitive
principles also contribute to an improved quality of intercrop products.
The inclusion of N2 fixing crops in an intercrop leads to the utilisation of
the renewable resource of atmospheric nitrogen which increases the
sustainability of the agroecosystem. Intercropping can also be regarded as a
practice to increase the production of less stable crops such as grain legumes
and hereby contribute to lowering the protein deficit in EU at lower risk for
the farmer.
All
these potentials strongly comply with the guidelines set up in Agenda 2000 and
including ‘the European model of agriculture’, emphasising the production
of healthy, safe and high quality food considering animal welfare, and
environmentally sound production, especially in relation to reduced nitrate
leaching from agricultural land. The project also relate to the Community
policy of new preventive methods for improving plant health, since the diverse
crop community in an intercrop may prevent the rapid spreading of diseases and
pests. Intercropping is also relevant for integrated and conventional
agriculture aiming at reducing the input of resources in plant production.
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