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New: Principles of Sustainable Weed Management for Croplands
Announcing this new web item from ATTRA.
Principles of Sustainable Weed Management for Croplands
http://www.attra.org/attra-pub/weed.html
Abstract:
Weeds are invited guests into agricultural fields as the result of
management decisions and defying nature's principles. Managing
croplands in tune with nature's principles makes for fewer and less
costly weed problems. Strategies which utilize allelopathy,
intercropping, crop rotations reduce weeds considerably. A weed-free
design is discussed. A number of other weed control strategies are
discussed. Additional resources are listed at the end of the
publication.
The author is Preston Sullivan, agronomy specialist.
As a sampler, I have copied one section below titled "The Root Causes
of Weeds"
The Root Cause of Weeds
Have you ever noticed when a piece of land is left fallow
that it is soon covered over by annual weeds? If the field
is left undisturbed for a second year, briars and young
trees start to grow. As the fallow period continues, the
weed community shifts increasingly toward perennial
vegetation. By the fifth year, the fallowed field will host
large numbers of young trees in a forest region, or
perennial grasses in a prairie region. This natural
progression of different plant and animal species over time
is a cycle known as succession. This weed invasion, in all
its stages, can be viewed as nature's means of restoring
stability by protecting bare soils and increasing
biodiversity.
Weeds are evidence of nature struggling to bring about
natural succession. When we clear native vegetation and
establish annual crops, we defy ecological succession. Man
is, in effect, holding back natural plant succession, at
great cost in weed control. To better understand this
process, think of succession as a coil spring. Managing
cropland as an annual monoculture compresses the spring -
leaving it straining to release its energy as a groundcover
of weeds. In contrast, a biodiverse perennial grassland or
forest is like the coil spring in its uncompressed condition
- a state of relative stability with little energy for
drastic change (Figure 1) (2). Generally speaking,
biodiversity leads to more stability for the ecosystem as a
whole.
Monoculture
(Unstable Simple Community)
Biodiversity
(Stable Complex Community)
Figure 1. Monoculture vs. Biodiversity
Modern crop agriculture is typified by large acreages of a
single plant type, accompanied by a high percentage of bare
ground - the ideal environment for annual weeds to prosper
in the first stage of succession. Holding succession at bay
with such unstable ecosystems can only be managed with high
levels of inputs such as cultivation, mowing, herbicides and
fertilizers.
Having a high diversity of plants and animals increases the
stability of the whole system because harm to any one
species is less likely under diverse conditions than with
less diverse environments. For example, an insect outbreak
could wipe out a pure stand of crop because the insects can
easily move from one plant to the next and breed rapidly.
The insects can find their food easily and have few
predators or parasites to hamper them. The same insect
invasion occurring in a mixture of many plant types would be
less severe on any one type of plant because the insects
would have a harder time finding their preferred food. The
insects would be undernourished, have more difficulty
finding a mate, and have lower reproductive rates. The end
result is that the impact of an insect outbreak is much less
severe on the whole ecosystem where high biodiversity
prevails. Stability through biodiversity is one of nature's
fundamental rules.
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