The research has been carried out in 1996-2001 under the conditions of loess soil of the central Lubelszczyzna. The experiment was set up following the randomized blocks method in three replications. The analysis of field infestation was made prior to spring barley harvest with the botanical-weighing method. It has been shown that the seven-year monoculture of spring barley increased significantly the number and air-dry weight of weeds as compared with the crop rotation. Barley cultivars did not differentiate the weed infestation. The plots were mostly grown by short-lived species of the fourth and fifth degree of phytosociological constancy. Spring barley in monoculture increased the occurrence of a majority of weed species, particularly Matricaria maritima ssp. inodora, Echinochloa crus-galli, Stellaria media, Viola arvensis, Chenopodium album, Chamomilla recutita, Galinsoga parviflora, Galeopsis tetrahit and Agropyron repens.

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