From steved@ncatark.uark.edu Tue Feb 1 18:37:56 2000 Date: Tue, 1 Feb 2000 16:52:54 -0600 From: Steve Diver To: sanet-mg@ces.ncsu.edu Subject: 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. =========================================== To Unsubscribe: Email majordomo@ces.ncsu.edu with the command "unsubscribe sanet-mg". If you receive the digest format, use the command "unsubscribe sanet-mg-digest". To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command "subscribe sanet-mg-digest". All messages to sanet-mg are archived at: http://www.sare.org/san/htdocs/hypermail