Effects of soil tillage and post-emergence weed control on weed biomass and maize yield

The three-year study was carried out on lessive pseudogleic soil in North-eastern Croatia. Effects of tillage intensity (mouldboard-, chisel plough, disk harrowing) and sulfonylurea herbicide combinations were evaluated on dry biomass of certain life cycle weed groups and on maize grain yield. Annual grass of Echinochloa crus-galli (L.) PB. was the main species in all years, with dry biomass reaching from 175 to 305 g m(-2). E. crus-galli biomass was significantly greater in chisel plow and disk harrowed plots than in mouldboard plow plots. No significant tillage effect was recorded for biomass of annual broad-leaved and perennial weeds. The differences in total weed biomass between mouldboard ploughing and reduced tillage practices as well between years were considerable. All herbicide combinations provided consistent biomass control of annual grass weeds (91-98%) and annual broad-leaved weeds (86-95%) but inadequate control of perennials (45-87%) on average. Nicosulfuron + 50% prosulfuron & 30% primisulfuron-methyl gave the best total weed control effect, followed by rimsulfuron + thifensulfuron-methyl and rimsulfuron + 50% prosulfuron & 30% primisulfuron-methyl without any significant effect on the yield. Maize yields were significantly affected by year and tillage. Tillage, which included mouldboard ploughing, gave significantly higher yields and showed higher resistance to weather conditions than less intensive tillage.