Water in the Soil - Agroecology: The Ecology of Sustainable Food Systems - page 127

FIGURE 9.11 Redwood bark mulch on the tops of strawberry beds near Aromas, California.

Artificial Mulches
A range of specially manufactured papers and plastics are
now available for use as mulches. Such materials can be
easily spread out and firmly secured to the soil surface.
When these “mulches” are spread directly over planted
beds, slits or holes can be made for the crop plants.
Moisture loss is greatly reduced and crop yields, very
often, are increased. Some plastics provide a concentrated
greenhouse effect as well, raising soil temperatures
several degrees. This is a very important benefit for crops
that are planted during the colder time of the year, such
as strawberries in coastal California (Figure 9.12).

cover to reduce evaporative losses from the surface. In no-
till systems, seeds are sown directly into the sod or under
residues of the previous crop with no plowing or disking,
allowing the plant material to remain as a barrier to evapo-
rative loss. Stubble mulching is a common practice in
subhumid and semiarid areas where enough biomass is
produced by the previous crop to provide sufficient soil
cover. The residue is chopped or mown, spread evenly over
the surface, and then special tillage implements that can
penetrate the mulch are used to plant the following crop.
Despite their positive impact on soil moisture, reduced
tillage systems have potential drawbacks. These include
increased dependence on herbicides for weed management,
buildup of soil pathogens from crop residues, and the need
for more complex and costly farming equipment.

Crop Residues and Reduced Tillage
By leaving a high percentage of the residue from the crop-
ping season on the surface of the soil, a protective barrier
that lowers evaporation is created. The residue mulch pro-
tects the boundary layer at the surface of the soil and
provides a barrier against the capillary flow of water to the
surface. The lower temperatures created by the mulch bar-
rier probably help reduce evaporation as well.
Reduced tillage and no-till techniques are often com-
bined by using crop residues as mulch. A major goal of
most reduced tillage systems is to develop greater soil

Soil Mulch
Natural soil mulch made from a cultivated dry soil layer
on the surface of the soil can conserve moisture in regions
with a distinct alternation between the wet and dry season.
This dry layer breaks the capillary flow of water to the
surface, and the process of its creation eliminates weeds
that might tap moisture below the dry layer and increase
transpirational losses. These benefits, however, must be