The aim of the present studies carried out over 1994-1998 was to define the effect of multi-year fertilisation with straw + NPK, NPK only, manure only, manure with: PK, NK, NP, NPK, NPK + Ca and no fertilisation on the weed infestation of cereals cultivated in crop rotation. The weed infestation was evaluated in a static fertilisation experiment established in 1948 at Mochełek in the vicinity of Bydgoszcz on typical lessive soil, IVa valuation class, of very good rye complex. Weeds dominating in spring barley included Spergula arvensis and Chenopodium album, and in winter wheat Viola arvensis and Apera spica – venti. The lowest amount of air-dry matter of weeds in spring barley was observed for multi-year fertilisation with manure and with NPK + Ca and with no fertilisation. In winter wheat, however, low weed infestation was also recorded for fertilisation with manure only and with manure + PK.

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