The objective of the studies was to assess the changes in weed seedbank over 5-year period. Two terms were considered in the experiment: (1) soil preparation for organic farming (2004-2005) and organic plant cultivation with crop rotation (2005-2008). Three variants of cereal crop sequence (A - oats - winter rye, B - oats - spring triticale, C - spring triticale - spring triticale) were included in two-year period of conversion. Over the three years of organic cultivation, a significant increase of weed species diversity in each examined layer was observed in comparison with seed species number determined after soil conversion. Strongly dominant species in both terms of the study was Chenopodium album, which has declined in its number over three years of the organic cultivation. Among the weed species, which did not appear during conversion but have appeared after organic cultivation Erigeron canadensis was noted in the highest number.
