Agriculture Reference
In-Depth Information
FIGURE 15.6
The traditional corn-bean-squash inter-
crop system from Mesoamerica.
Complex species interac-
tions are key to the success of this cropping system.
•
Herbivorous insects are at a disadvantage in
theintercrop system because food sources are
less concentrated and more difficult to find in
themixture (Risch, 1980; Verkerk et al., 1998).
Our knowledge of the ecological mechanisms of inter-
ference that function in this crop community provides a
tantalizing indication of what we can look for in mixtures
anywhere farming occurs.
An enormous number of polycultures exist, reflect-
ing the wide variety of crops and management practices
that farmers around the world use to meet their require-
ments for food, fiber, feed, fuel, forage, cash, and other
needs. Intercrop communities can include mixtures of
annuals, annuals with perennials, or perennials with
perennials. Legumes can be grown with an array of cere-
als, and vegetable crops may be grown in between rows
of fruit trees. The patterns of planting such mixtures can
range from alternating rows of two crops to complex
assortments of annual herbs, shrubs, and trees, as found
in home garden agroecosystems (Chapter 17). Planting
and harvesting in polycultures can be distributed in both
time and space to provide advantage to the farmer
throughout the year. The integration of animals helps
form even more fully integrated mixed-crop communi-
ties (Chapter 19). Understanding the ecological founda-
tion of the interactions that take place in these crop
communities is the key to returning polyculture to prom-
inence in agricultural practice.
•
The presence of beneficial insects is promoted
due to such factors as the availability of more
attractive microclimatic conditions and the
presence of more diverse pollen and nectar
sources (Letourneau, 1986; Verkerk et al.,
1998).
Interestingly, when the same varieties of corn, bean,
and squash were simultaneously planted in the same way
in a nearby soil that had at least 10 years of management
history involving mechanical cultivation, synthetic chem-
ical fertilizers, and modern pesticides, the yield advan-
tages disappeared. Apparently, the positive interactions
that occurred in the traditional farm field were inhibited
by the alteration of the soil ecosystem, which occurred
with conventional inputs and practices. This result points
to an important link between cultural practices and eco-
logical conditions.
The corn-bean-squash intercrop is only one of many
crop combinations that either exist or could be developed.
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