Environmental Engineering Reference
In-Depth Information
9.4.2.4 Mulching and solarization
A relatively non-destructive method of killing weeds and invasive plants in some
situations is the use of mulches and solarization. The purpose of mulches used for
weed control is to exclude light from germinating plants, which inhibits photo-
synthesis and causes the plants to die (Radosevich
et al
. 2007). Some of the more
commonly used mulches include straw, bark, manure, grass clippings, sawdust,
rice hulls or other crop residues, paper, and plastic. Artifi cial mulches made of
woven plastics are also available—these exclude particular wavelengths of light but
allow water, nutrients, and air to penetrate into the soil. Mulches are most effective
for controlling small annual weeds but larger plants and some perennials can also
be suppressed by using mulches. Mulching is commonly used in agriculture, home
gardens, and landscapes, but can be used in some wildland areas as well. Organic
mulches that have not been composted or degraded have been shown to reduce
available soil nitrogen due to nitrogen immobilization by soil microfl ora, which
use the mulch as a food source (Zink and Allen 1998). Mulching with organic mat-
ter in this way has been used to suppress nitrophilous exotic species and promote
establishment of native species during restoration efforts (Zink and Allen 1998;
Reever and Seastedt 1999).
Soil solarization is performed by covering moist tilled soil with clear plastic—
which permits light to pass through—to kill imbibed weed seeds (Horowitz
et al
. 1983). h e plastic sheets are left covering the soil surface for about 4 weeks.
Long periods of high intensity solar radiation that elevate temperature in moist soil
under the plastic are required for best results. Weed seeds are killed either by the
prolonged period of high temperature or by other factors. For example, high tem-
perature stimulates germination of some seeds but seedlings cannot survive under
the plastic (Horowitz
et al
. 1983). Solarization was initially developed for control
of soil microfl ora and microfauna, which can also be injured or killed by this prac-
tice (Horowitz 1983). Solarization has also been investigated for use in restoration
of wildlands, such as grasslands and abandoned farmland, to reduce abundance
of resident exotic weeds prior to planting native species (Bainbridge 1990, 2007;
Moyes
et al
. 2005).
In agricultural or natural resource production systems, cultural methods of weed
suppression often occur during the normal process of land preparation and crop
production (Radosevich
et al
. 2007). Some of these practices are also relevant for
the control of invasive plants in wildlands, such as prevention and using competi-
tion against unwanted plants.
9.4.3.1 Prevention
Surveys and monitoring are the fi rst step in prevention of invasive plants in wild-
land ecosystems or natural resource production systems other than agriculture
(Dewey and Anderson 2004). The prevention or quarantine of a weed problem is
