In a three year study (1994-96) reduced soil tillage variants proved satisf
actory for winter wheat grown on Humogley soil in Eastern Croatia in the ab
sence of herbicides. During the experiment the conventional tillage (plough
ing, disk-harrowing, standard sowing) did not give significantly higher yie
lds compared to the reduced tillage treatments (disk-harrowing; tillage by
multitiller with chisels; seedbed preparation (rototiller) + sowing by roto
sem; and ploughing, seedbed preparation + sowing by rotosem). Production of
weed biomass at the conventional tillage equalled the treatment tillage by
rototiller + sowing by rotosem, but was significantly lower than in other
tillage treatments. Totally, nitrogen fertilisation had a significant influ
ence upon wheat yield increase at each N level (140, 170, and 200 kg ha(-1)
), whereas the efficacy of fertilisation upon yields was higher at reduced
tillage treatments without ploughing than at the conventional tillage. The
correlation between crop yield and weed biomass decreased along with the in
crease of N level. Winter wheat had a higher N optimum than its weed compon
ent, which points out that for this crop N fertilisation at reduced tillage
systems can be used as a measure for weed control The reduced tillage vari
ant with rototiller + sowing by rotosem turned out to be entirely competiti
ve with the conventional tillage regarding yield and weed biomass, as well
as a higher resistance to weather conditions.