Temperature - Agroecology: The Ecology of Sustainable Food Systems - page 66

TABLE 5.1
Schematic microclimatic profile of a mature corn/bean/squash intercrop system, showing relative levels of
five factors at each layer in the canopy at midday

Temperature Wind speed Water vapor Light

CO 2

above corn

canopy

upper corn

canopy

mid-interior

below squash

leaves

soil surface

highest level low level

high level lowest level

medium level

Source: adapted in part from Montieth 1973

M ODIFYING THE T EMPERATURE M ICROCLIMATE

Canopy Vegetation

Through appropriate design and management, the micro-
climate of a system can be modified. Such modification
is especially important if the goal of the farmer is to
create or maintain microclimatic conditions that favor
the sustainability of the cropping system. If this is the
case, each modification must be evaluated as much as
for its contribution to short-term yield and market return
as for its contribution to the longer-term sustainability
of the system.
Although microclimate includes many factors, its
modification is often focused specifically on temperature.
Practices and techniques used to modify the temperature
microclimate are described below. Although modification
of temperature is the main purpose of these practices, they
will also impact other factors of the microclimate, such as
humidity and light.

Trees or other tall plants that create a canopy over the
other plants in a system can greatly modify the tem-
perature conditions under the canopy. Shade from the
canopy reduces solar gain at the surface of the soil, as
well as helps the soil retain moisture. Agroforestry
systems in the tropics are a good example of this kind
of practice.
The data from a study in Tabasco, Mexico (Gliess-
man, 1978c) clearly show the temperature-modifying
effects of trees. In this study, the temperature microcli-
mate of a tree-covered cacao orchard was compared
with that of a nearby open grass pasture. As shown in
Figure 5.6, temperature changes over a 24-h period at
various levels in the cacao plantation were much more
moderate than they were at the same levels in the pas-
ture system. The pasture system became warmer during