WEED POPULATIONS OF WINTER WHEAT AS AFFECTED BY TILLAGE AND NITROGEN

Kneževic M., Stipesevic B., Kneževic I., Loncaric Z.: Weed populations of winter wheat as affected by tillage and nitrogen. Ekologia (Bratislava), Vol. 26, No. 2, p. , 2007. A three-year study was conducted for winter wheat after soybean on humogley soil in north-eastern Croatia to evaluate the effects of five tillage systems (CT – conventional tillage with mouldboard ploughing; DH – disk harrowing; MT – multitiller; RT – rotosem; PR – mouldboard ploughing + rotosem) and four nitrogen (N) levels (0, 140, 170, 200 kg N.ha –1 ) on weed species composition, plant density, and plant dry weight in the absence of herbicide. Annual species of Ambrosia artemisiifolia L., Chenopodium album L., Galium aparine L., Polygonum lapathifolium L. and Stellaria media L. were dominated in all three years. The density of total weeds was significantly affected by tillage and it ranged across from 9.6 plants after RT to 28.2 plants.m–2 after PR tillage. No significant differences in total dry weight were found between CT and RT, which had the lowest dry weight from 17.4 g and 19.6 g.m–2, respectively. An increased level of applied nitrogen tended to significantly decrease total weed density from 21.0 plants at N0 to 13.6 plants.m –2 at N200. In a three-year average, no significant differences in weed dry weight were observed between N170 and N200 levels which gave approximately 21% and 16% higher dry weight compared to N140 level, respectively. No significant differences in dry weight of Galium aparine populations were found between all three nitrogen levels after CT and RT tillage treatments. Total weed density and weed dry weight were poorly correlated within all tillage x nitrogen combinations (r 2 values of 0.10 to 0.48). That suggests that tillage and N fertilisation levels can be utilized as a strategy in weed control management for winter wheat on humogley soil.