Experiments were conducted during 1996-99 in Poland to study the effect of sowing density on barley, oat, wheat and triticale weed infestation. The cereals were sown in 4 densities, starting from 400 grains of barley and 650 grains of the other species (100%) and consequently reduced to 80, 60 and 40%. Number and weight of weeds in each year was seriously diverse. Weed infestation was the smallest (mean 27 weeds/m 2) at high sowing density and increased with a decrease in sowing density, reaching 88 weeds at the smallest density of cereals. The reduction of sowing density by 20% increased weed density 40-50%. The most frequent weeds were Setaria viridis and cultivated rape ( Brassica napus var. oleifera).
