The aim of the research was to determine the effectiveness of various methods for breaking seed dormancy of weed species Johnson grass (Sorghum halepense (L.) Pers.) and their influence on germination and seedlings growth. Beside control treatment, eight treatments for breaking dormancy of seeds were applied: seed immersion in distilled water for 24 hours; seed immersion in water at 60 °C for 1 hour; immersion in a 0.2% solution of potassium nitrate for 24 hours; immersion in 2% solution of sodium hypochlorite for 8 hours; treatments with concentrated sulphuric acid for 5 and 10 minutes; treatment with concentrated sulphuric acid for 5 minutes and germination in darkness; and combined treatment of sulphuric acid (5 minutes) and 1.5% potassium nitrate solution (2 hours). Average germination of Johnson grass seeds in control treatment was very low, only 2.8%. All dormancy breaking treatments increased seed germination and the highest germination was observed in treatment with combination of sulphuric acid and potassium nitrate (35.0%) and treatment with 2% sodium hypochlorite (30.6%). However, sodium hypochlorite reduced root length of seedlings for 40.9% compared to control, while all treatments had a positive effect on Johnson grass shoot length. Total seedlings length was the highest when seeds were treated for 5 minutes with sulphuric acid. None of the treatments showed significant effect on Johnson grass seedlings fresh weight. Seed germinated fastest in treatment with a combination of sulphuric acid and potassium nitrate (4.58 days), and slowest when seeds were immersed in water (8.16 days) and in the 2% solution of sodium hypochlorite (8.92 days).Cilj istraživanja bio je utvrditi učinkovitost različitih metoda prekida dormantnosti sjemena korovne vrste divlji sirak (Sorghum halepense (L.) Pers.) odnosno njihov utjecaj na klijavost i rast klijanaca. Uz kontrolni tretman, primijenjeno je osam tretmana za prekidanje dormantnosti sjemena: potapanje sjemena u destiliranu vodu tijekom 24 sata; zagrijavanje u vodi na 60 °C tijekom 1 sata; potapanje u 0,2% otopinu kalijevoga nitrata tijekom 24 sata; potapanje u 2% otopinu natrijevoga hipoklorita; tretiranje koncentriranom sumpornom kiselinom tijekom 5 i 10 minuta; tretiranje koncentriranom sumpornom kiselinom tijekom 5 minuta i naklijavanje u tami, te kombinirani tretman sumporne kiseline (5 minuta) i 1,5% otopine kalijevoga nitrata (2 sata). Prosječna klijavost sjemena divljeg sirka u kontrolnom tretmanu bila je vrlo niska, svega 2,8%. Svi tretmani prekidanja dormantnosti povećali su klijavost sjemena, a najviša klijavost zabilježena je u tretmanu s kombinacijom sumporne kiseline i kalijevoga nitrata (35,0%) te u tretmanu s 2% otopinom natrijevoga hipoklorita (30,6%). Međutim, primjena natrijevoga hipoklorita smanjila je duljinu korijena klijanaca divljeg sirka za 40,9% u odnosu na kontrolu, dok su svi tretmani imali pozitivan utjecaj na duljinu izdanka divljeg sirka. Ukupna duljina klijanaca bila je najviša kod tretiranju sjemena sumpornom kiselinom tijekom 5 minuta. Tretmani nisu pokazali značajan utjecaj na svježu masu klijanaca divljeg sirka. Najbrže je klijalo sjeme u tretmanu s kombinacijom sumporne kiseline i kalijevoga nitrata (4,58 dana), a najsporije kod potapanja sjemena u vodu (8,16 dana) te u 2% otopinu natrijevoga hipoklorita (8,92 dana)
