Effects of soil tillage and nitrogen on winter wheat yield and weed biomass

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.