Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 215

emerge successfully only near the soil surface (Rubin & Benjamin, 1984). Thus,
shifts in weed species composition should be expected following solarization,
and the need for additional management tactics should be anticipated.
In addition to weed suppression, advantages of soil solarization include
suppression of soil-borne crop pathogens, such as Verticillium dahliae and
Fusarium oxysporum , and increases in crop yield (Katan, 1987; Bell, Elmore &
Durazo, 1988; Kumar et al ., 1993; Stapleton & DeVay, 1995). Disadvantages
include the reliance on a relatively expensive input (polyethylene mulch); a
lack of fully effective control of many perennial and some annual weed
species; the need to remove and dispose of large amounts of plastic; and the
need to take a field out of production, albeit temporarily (Bell, Elmore &
Durazo, 1988). Because the cost of solarization is high ($750 to $1500 ha 1 -
Stapleton & DeVay, 1995), the technique is most appropriate for high-value
crops that would otherwise have large labor requirements and significant
expenses for weed control.The development of new thin-layer mulch materi-
als that are temporarily effective for sealing the soil surface, but which are
photodegradable or biodegradable,has been suggested as a means of lowering
the costs of solarization and mulch disposal (Stapleton & DeVay, 1995). Also
needed is research to identify how solarization can be combined with other
management practices for better control of a broader spectrum of weed
species. For example, Elmore, Roncoroni & Giraud (1993) found that control
of the perennial grass Cynodon dactylon by solarization was improved by tillage
prior to applying polyethylene tarps.As noted later in this chapter (see section
“Residue effects on weed and crop performance”), residues of certain crop
species suppress weeds chemically as the residues decompose. Incorporation
of cover crop residues into soil before solarization can increase control of soil-
borne plant diseases (Gamliel & Stapleton, 1997) and this combination of
practices might also increase weed suppression.
Water management
Drainage and irrigation are widely used to improve soil moisture con-
ditions for crop production. Conversely, water can be added or withheld to
prevent weed germination, or to stress or kill weeds. Weed suppression
through moisture management can be achieved through non-selective
methods, used when crops are absent, and selective methods, used when
weeds are growing in mixture with crops. The reactions of individual weed
species and weed communities to moisture manipulations are determined
by the timing, location, and magnitude of alterations of soil moisture
conditions.