EFFECTS OF SOIL TILLAGE AND HERBICIDES ON WEEDS AND WINTER WHEAT YIELDS

The effects of three tillage systems and the post-emergence chemical weed control of annual broad-leaved weeds in winter wheat were studied on lessive pseudogley soil in north-eastern Croatia from 2001 to 2006. Total weed biomass on untreated plots was the lowest in continuous mouldboard ploughing (49.8 g m(-2)), medium in chisel ploughing (90.9 g m(-2)) and highest in continuous disk harrowing (187.3 g m(-2)) with statistically significant differences (P < 0.01). The most abundant weeds were annual broad-leaved species of Matricaria inodora, Ambrosia artemisiifolia, Galium aparine, and Stellaria media, which constituted 57, 56 and 41% of total weed biomass in mouldboard-, chisel ploughing and disk harrowing, respectively. Three herbicide mixtures of 5% iodosulfuron - methyl sodium + 15% mefenpyr-diethyl; 12% fluoroglycofene-ethyl + 6% triasulfuron and 54% 2,4-D ethylhexyl ester + 0.5% metosulam in low doses provided a successful biomass control of dominant annual broad-leaved weeds (89-100% control). Herbicide treatments gave significantly higher yields than untreated controls with an average yield increase of 3, 11 and 7% in mouldboard-, chisel ploughing and disk harrowing, respectively. The yields did not differ among herbicide mixtures. Compared to the highest yield with mouldboard ploughing (6.1 t ha(-1)), average yield depressions with chisel ploughing and disk harrowing were 3 and 5%, respectively.