TILLAGE AND NITROGEN INFLUENCE WEED POPULATION-DYNAMICS IN BARLEY (HORDEUM-VULGARE)

Field experiments were initiated at Alliance and Hairy Hill, Alberta, in 1989 to investigate the effects of conventional tillage, zero tilla ge, and our levels of nitrogen fertilizer on continuous barley product ion. In both tillage systems, the nitrogen was banded 6 to 8 cm deep b etween alternate barley rows. Herbicides were used for weed control ea ch year. The influence of tillage and nitrogen on weed seed population dynamics was determined in 1991 and 1992. In the zero-tillage system, a large proportion of the weed seeds were present either at the soil surface or at the 5- to IO-cm depth. Green foxtail, the dominant speci es at Alliance, was also present at Hairy Hill where field pennycress was dominant. Green foxtail was consistently associated with low (resi dual) nitrogen and, in most cases, with conventional tillage, At both locations, green foxtail populations tended to decrease to very low le vels as nitrogen rate. increased, especially in zero tillage. At Hairy Hill, held pennycress populations in the soil seedbank: were higher i n zero tillage compared with conventional tillage, but plants that eme rged from the soil seedbank in the field in spring were lower in zero tillage. Field pennycress populations were highest under low nitrogen. The results indicate that banding nitrogen has the potential to be an effective tool for green foxtail and field pennycress management in c onventional-and zero-tillage systems, resulting in less dependence on herbicides for their control.