Structural changes of weed communities on highly-N-supplied fields under extensified agricultural practice
1994
Bischoff, A. (Halle-Wittenberg Univ., Halle (Germany). Inst. fuer Geobotanik und Botanischer Garten) | Mahn, E.-G.
The regeneration process of an agro-ecosystem on chernozem soil (Bad Lauchstaedt) highly eutrophicated by organic manuring till 1984 is investigated in the course of an integrated research project (STRAS). Although a distinct decrease of the soil nutrient contents is visible, a corresponding structural change in the plant community is not observed. The species composition is quite different from that of a long-term experimental field (Etzdorf, 10 km away), where one canfind the weed community typical for the site (Euphorbio-Melandrietum) on plots without herbicide use. Especially the characteristic species of this community are rarely found on the highly-N-supplied field and are almost absent in the soil seed bank. Reasons could be seen in the herbicide use till 1990 and in the lack of immigration chance because of the scarcity of these species in the vicinity. Furthermore in such a dense stand resulting from high biomass production there is an increased risk of extinction for just immigrated species with low population densities. On the highly-N-supplied field a greater tendency to produce dominant stands is noticed. 1990 Chenopodium album was dominant, in the following year Descurainia sophia. So in spite of similar species numbers the diversity (evenness) is lower than on the long-term experimental field. Because this tendency was very distinct on the plots which lay fallow before, at the present state of knowledge a one year fallow cannot be assessed as a suitable method to regenerate such an agro-ecosystem
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