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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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