The objective of this research was to study of weediness in connection with nutrient supply. The composition of weed flora, number of species, density and dominance of weed species were examined in a long-term fertilisation experiment, which was set up in 2003 in Nagyhörcsök, Hungary. Weed survey was carried out in control (Ø) and NPK (150 kg ha-1 N, 100 kg ha-1 P2O5, 100 kg ha-1 K2O) treatments with 3 replications in 2013 and with 6 replications in 2014, both at 2–4 leaf phenological stage of maize (BBCH 12–14). Weeds were collected from 1 m2 herbicide-free (weedy) sampling areas in every plot.

The experimental data showed strong correlation between weed density and nutrient supply. 12 weed species occurred on the studied plots in 2013, 7 in the control and 11 in the NPK treatment. The total weed density was significantly higher in the plots with good nutrient supply – by 65 % as compared to the control. Ambrosia artemisiifolia L., Sorghum halepense (L.) Pers. and Datura stramonium L. were present in both nutrient treatments and these weed species had the highest density. The order of dominance was also different depending on the applied nutrient treatments. A. artemisiifolia (0.625) was the most dominant weed species in the plots without nutrients (Ø) and C. album (0.520) in the plots with good nutrient supply (NPK). Nearly one year later 16 weed species occurred on the studied plots, 15 species in the control and 14 species in the NPK treatment. The average weed density was 120.4 plant m-2 in the control and 109.1 plant m-2 in the plots with good nutrient supply. The order of dominance was similar to the previous year.

According to the results many similarities could be found between the experimental years. Considering the density and order of dominance of weed species in the different treatments, the interspecific competition is clearly outlined.

Keywords: maize, nutrient supply, weed density, dominance, Ambrosia artemisiifolia L.