Humidity and Rainfall - Agroecology: The Ecology of Sustainable Food Systems - page 81

In all of these regions, grain crops are the primary focus.
In Australia, however, wheat in rotation with grazing,
especially for sheep and wool production, has led to the
development of unique systems where a grain crop is
grown alternately with pasture. Pasture actually allows
for the replenishment of moisture reserves necessary to
produce a grain crop.
A unique example of dry farming occurs in coastal
central California, where several vegetable crops are
planted, either from transplanted seedlings or direct seed-
ing, at the beginning of the dry Mediterranean summer
in May. Rarely does rainfall occur in summer in this
climate; so these vegetable crops must rely solely on the
moisture reserves stored in the soil. Tomatoes seem to be
a crop that is particularly well suited to this system.
Tomato seedlings are planted deeply into moist soil in
May, with no irrigation applied. Cultivation of the soil
surface maintains a weed-free dust mulch, and because
the soil surface is dry and no rain occurs during the
growing season, the plants are not staked or tied, and
fungal disease is a minor problem. Harvest begins in late
August and continues until the first rains of the new
wet season, usually in late October or early November.

Tomatoes harvested from this system have a reputation
for more concentrated flavor (Figure 6.5).
The sustainability of dry farming systems must be
weighed against the potential loss of soil organic matter
from the upper soil levels with the dust mulch system, the
danger of soil erosion from wind and rain because of the
low level of soil cover, and the unpredictability of soil
moisture availability as a result of variable rainfall during
the fallow period. But as a way of farming in areas with
low and upredictable rainfall, dry farming can be a low
external-input alternative.

WATER HARVESTING SYSTEMS
IN ARID REGIONS

In warm regions of the world with arid climates (less
than 250 mm annual precipitation), lack of rainfall is a
severe limiting factor for agriculture. In many such
places, however, rainfall does occur with some regularity
in the form of short, torrential showers, and it is possible
to “harvest” this water by collecting and concentrating
rainfall runoff.

FIGURE 6.5 Dry-farmed tomatoes, Santa Cruz, CA. A cultivated soil mulch keeps moisture close to the surface and controls
weeds during the rainless summer growing season.