Agriculture Reference
In-Depth Information
cesses. It is time to redirect a large portion of the resources
that have generated all of the knowledge about single-
species cropping systems toward the integration of both
ecological and agronomic knowledge, and to do so with
the broader goal of developing the ability to manage the
entire community of interacting organisms, both crop and
noncrop, and understand how each species contributes to
the sustainability of the whole system. This is an
extremely complex process, requiring a systems-level
approach and the interaction of many disciplines, but the
end result will be a better understanding of how effective
change in agriculture can come about.
TA B L E 1 5 . 3
Yield of a Corn-Bean-Squash Polyculture
Compared to Yields of the Same Crops Grown as
Monocultures in Tabasco, Mexico
Low-Density
Monoculture a
High-Density
Monoculture a
Polyculture
Corn density
(plants/ha)
40,000
66,000
50,000
Corn yield
(kg/ha) b
1150
1230
1720
Bean
density
(plants/ha)
64,000
100,000
40,000
FOOD FOR THOUGHT
Bean yield
(kg/ha) b
740
610
110
1.
What are some of the primary impediments to
convincing conventional farmers of the poten-
tial advantages of managing complex, multi-
species cropping systems?
Squash
density
(plants/ha)
1875
7500
3330
Squash yield
(kg/ha) b
250
430
80
2.
Give an example of a complex cropping com-
munity where competition and mutualisms may
play different but equally important roles in the
success of the entire crop system.
Land
equivalent
ratio (LER)
1.97 c
1.77 d
3.
Describe an example of how coexistence and
mutualisms in a crop community can be essen-
tial to the success of a biological control mecha-
nism for a particular crop pest.
a The monoculture densities were designed to represent levels just
above and below the normal monoculture planting densities.
b Yields for corn and beans expressed as dried grain, squash as fresh
fruits.
c Compared to low-density monoculture.
d Compared to high-density monoculture.
4.
A noncrop organism can have either positive
or negative impacts on the rest of the crop
community of which it is a member. Explain
how this is possible.
Source : Amador, M. F. 1980. Comportamiento de tres especies (Maiz,
Frijol, Calabaza) en policultivos en la Chontalpa, Tabasco, Mexico .
Tesis Profesional, CSAT, Cardenas, Tabasco, Mexico.
5.
Describe a complex cropping community of
crop and noncrop populations that allows for a
significant reduction in the use of nonrenewable
synthetic agricultural chemicals. Be sure to
explain the contribution made by each member
of the crop community.
USING SPECIES INTERACTIONS FOR
SUSTAINABILITY
In natural ecosystems, organisms occur in communities
of mixed species assemblages. Our ability to understand
the complexity of interactions going on in such mixtures
has benefited greatly from a growing body of ecological
knowledge focused at each of the four levels of organiza-
tion in ecosystems. The community ecology level dis-
cussed in this chapter is based on an understanding of the
individual organism level and the population level. At the
community level of organization, unique qualities begin
to emerge as a result of multispecies interactions. These
qualities have importance at the ecosystem level, as we
will see in following chapters.
The challenge for agroecologists, then, is to put this
ecological understanding into the context of sustainability.
It is important that we combine the agronomists' extensive
knowledge of the ecology and management of single spe-
cies populations of crops with the ecologists' extensive
knowledge of species interactions and community pro-
6.
What are several “emergent qualities” of a crop
community that are not evident at the popula-
tion or single individual level in an agroeco-
system?
INTERNET RESOURCES
Agroecology in Action
www.agroeco.org
The website of Professor Miguel Altieri, at
University of California, Berkeley, with ex-
tensive material on agroecological pest and
habitat management.
Community Ecology Group, NERC Center for
Population Biology (Great Britain)
www.cpb.bio.ic.ac.uk/communityecology/
communityecology.html
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