Agriculture Reference
In-Depth Information
No row covers
No row covers
(1987-88)
Row covers on organic treatment
Row covers on organic treatment
(1988-89)
(1987-88)
(1988-89)
220
220
Row covers
removed Feb 20
Row covers
removed Feb 20
Conventional
118
118
CC°
CC°
116
116
Conventional
114
114
Organic
Organic
112
112
Jan 12
Jan 27
Feb 23
Mar 8
Mar 22
Dec 28
Jan 22
Jan 29
Feb 12
Feb 19
Mar 5
FIGURE 5.7
Effect of floating row covers on soil temperature in an organic strawberry system.
When strawberries are grown
under conventional methods, it is possible to use clear plastic as a soil-temperature-elevating soil covering during the winter, because
weeds have been killed by prior soil fumigation. In organically-grown strawberries, black plastic must be used instead to prevent
weed growth. Black plastic, however, is less efficient than clear plastic in raising the soil temperature, as shown in the left-hand
graph. In an attempt to compensate for this difference, nylon floating row covers were placed over the organic strawberries during
the second year of the study. As shown in the right-hand graph, the row covers were successful in narrowing the soil temperature
differences between the conventional and organic treatments during the period the covers remained on the beds. (Data from Gliessman
et al., 1996.
California Agriculture
50: 24-31.)
winter where light frost becomes possible. Due to their high
cost, these structures are mostly restricted to use with higher
value crops (Figure 5.8).
usually considered a problem in waterways, especially
in tropical areas, can be pulled from the water and
applied as mulch. Plant-derived mulches eventually
get incorporated into the soil, benefiting soil organic
matter content. In recent times, some nonplant mulch-
ing materials have become popular; these include
newspaper, cloth, and plastic sheeting. Specialized hor-
ticultural papers have been developed that biodegrade
after a period of time and can be worked back into
the soil.
A practice with effects similar to those of adding a
mulch is to let a mulch accumulate naturally. This is
accomplished through the use of a no-till system. Crop
residues are left on the soil surface, forming a mulch
that modifies the temperature of the soil and prevents
moisture loss.
A final kind of practice is to change the color of the
soil surface; to alter its albedo and the amount of solar
energy it absorbs. Burning crop residue is one way of
doing this. Residue burned to carbon black will absorb a
greater amount of heat, and residue burned to ash white
will absorb less heat.
Soil Surface Cover
Changes in the soil temperature microclimate can be
induced by covering the surface of the soil. Growing a
cover crop is one well-recognized method of modifying
soil temperature. The cover crop shades the soil, hence
lowering soil temperatures, and has additional positive
impacts on soil organic matter content, weed seed
germination, and moisture conservation. When a cover
crop is planted in between active crop plants, it is often
called a
living mulch
.
A living mulch can change the
albedo of the soil surface, making it less reflective and
raising the temperature of the air immediately above
the crop. A living mulch can also have the opposite
effect on temperature by increasing evaporation off of
the vegetation.
Nonliving mulches, of either organic or inorganic
materials, can change the temperature microclimate as
well; their effect depends on the color, texture, and
thickness of the material. Straw from crops such as
wheat, oats, and barley are commonly used for a dry
mulch, as are many other kinds of crop residues or
grasses gathered from fallow fields, gardens, or nearby
noncrop areas. Aquatic plants such as water hyacinth
(
Eichornia crassipes
) or duckweed (
Lemna
spp.),
Greenhouses and Shade Houses
Shade houses and greenhouses are now common ways
of modifying the temperature environment at the micro-
climatic level. Shade houses block a portion of incom-
ing solar radiation, lowering solar gain and temperature.
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