| Summary: | The paper analyses the weeds community in oats cultivated at different position in two crop rotations: after potato (in the rotation system with 25% share of oats) and twice after oats (with its 75% share) during the years 1990-2000, using the diversity of species indicators (by Simpson and by Shannon-Wiener), homogeneity of species by Simpson and communities similarity ratios. The dependence of biological indicators on the weather conditions and the dependence of oats grain yield on the number and diversity of species were assessed. Diversity and homogeneity of species in communities of weeds in the field of oats showed high differences from year to year of studies and dates of measurements (stage of oats tillering, end of its vegetation). To a lesser degree they changed under the influence of the position in the rotation system. With the passage of years the number of weeds during the spring period gradually increased. The analyzed parameters showed the differentiated dependence on the weather conditions. The communities form years with similar weather conditions did not show analogy in individual density and species. No significant dependence between the yield and the diversity of weeds was confirmed.
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