Temperature - Agroecology: The Ecology of Sustainable Food Systems - page 67

10 cm above soil surface

At soil surface

550

338

Pasture

334

440

Pasture

330

330

CC° CC°

Cacao
plantation

226

Cacao
plantation

220

222

118

Noon 4:00 8:00 12:00 4:00 8:00 Noon 4:00 8:00 12:00 4:00 8:00

PM AM PM AM

2 cm below soil surface 5 cm below soil surface

332

332

330 330

Pasture

Pasture

228 228

CC° CC°

226 226

224 224

Cacao
plantation

Cacao
plantation

222 222

Noon 4:00 8:00 12:00 4:00 8:00 Noon 4:00 8:00 12:00 4:00 8:00

PM AM PM AM

FIGURE 5.6 Temperature changes over a 24-h period at four different levels in an open pasture and in a tree-covered cacao
plantation in Tabasco, Mexico. The presence of trees in the cacao system moderates temperature changes at all levels, keeps
belowground temperatures lower than those in open pasture, and keeps aboveground temperatures higher at night. A similar pattern
is shown for relative humidity: in the pasture system, humidity fluctuates more over a 24-h period than it does in the cacao system.
Note that the scales on the vertical axes are not all identical (Data from Gliessman S.R., 1978c. Colegio Superior de Agricultura
Tropical).

the day than the cacao system, and became colder
aboveground during the night.

upper 5 cm of the soil were significantly raised during the
critical root and crown development period for the straw-
berry plant (Gliessman et al., 1996).
There has also been considerable research and practical
experimentation in the use of “hoop houses” or plastic tunnels
for vegetable production in California, Spain, and elsewhere
(Illic, 1989). Wire or plastic hoops are placed over planted
beds in the field, and then covered with plastic or cloth. The
localized greenhouse effect of these structures traps and holds
additional heat during the day, and the covering reduces heat
loss during the night. Hoop houses can allow for the earlier
planting of warm-weather crops such as tomatoes or peppers,
or the extension of the cropping season into the fall or early

Nonliving Canopies

Other means of creating a canopy for a cropping system
are possible as well. Floating row covers of nylon fiber,
for example, have been used over organic strawberries in
California during the early winter season in an attempt to
allow more insolation of the soil surface below, yet pro-
vide a localized greenhouse effect for reradiated heat given
off from the soil surface. Figure 5.7 shows the results of
one study of this practice, in which temperatures in the