The effect of different densities of Italian ryegrass (Lolium italicum L.: G1- 5 kg/ha seeds, 60 cm row spacing; G2- 5 kg/ha seeds, 20 cm row spacing; G3- 20 kg/ha seeds, 60 cm row spacing, and G4- 20 kg/ha seeds, 20 cm row spacing) and different rates of applied nitrogen fertilizer (N1- 0 kg N/ha; N2 - 50 kg N/ha; N3- 100 kg N/ha and N4-150 kg N/ha) on SPAD values under interaction between the crop and cleavers (Galium aparine L) was investigated. A tri-factorial trial (4 sowing rates x 4 fertilization rates x 4 sampling times) with three replications was set up in a random block design with plot size 10 m2 on a anthropogenious soil in the Šabac area in 2005/2006. SPAD was measured at 30 random plants of L. italicum and G. aparine on each plot four times during vegetation (V1- tillering; V2 - stem extension; V3- flagleaf, and V4-earing), and nitrogen content in plants was then computed. Relative nitrogen content in plant material was used as a parameter of competitive interaction between the cultivated and weed species. Total nitrogen in plant material was also analyzed. The data acquired showed that SPAD values were normally higher in L. italicum than in G. aparine under almost all crop densities and nitrogen rates applied, and maximum values were recorded in the third growing stage (flagleaf) at G3 density and treatment rate of 100 kg N/ha. The highest biomass yield (6 033.0 kg/ha) and seed yield (1 129.0 kg/ha) of Italian ryegrass were achieved in the same variants, i.e. at crop density of 5 kg/ha seeds, 60 cm row spacing and 100 kg N/ha fertilizer, and the crop developed in competition with the weed species G. aparine at an average population density of 15-25 plants/m2.

competition; density; Galium aparine; Lolium italicum; SPAD-502; nitrogen