This paper presents a study on the effect of a 26- to 31-year monoculture on the weed infestation of two oat cultivars with and without chemical control. The 6-year study was carried out in a static field experiment on podzolic soil formed of medium dusty clay at the Bałcyny Experimental Station. The control was made up of oat grown in a 6-field crop rotation: potato – oat – fibre flax – winter rye – horse bean – winter triticale. The oat cultivation in a 26-to-31-year monoculture resulted in a heavy weed infestation. In comparison to oat grown in crop rotation, the number of weeds per 1 m² in the uncontrolled oat monoculture was over 3-fold greater, while their biomass was over 4-fold greater. The herbicides applied had a similar effect on weed reduction in both fields (namely in crop rotation & monoculture), while their effect on the reduction in weed biomass was 68% greater in crop rotation than in monoculture (36% greater). We found similar weed infestation for the two oat cultivars grown in monoculture.

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