Influence of cultivation regime on weed floras of arable cropping systems.
The effects of different cultivation regimes on arable weed floras were investigated at 5 sites over several yr. At 3 sites arable crops were grown in rotation and at the remaining 2 sites cereals were grown in succession. Seedling densities at 2 sites were greater on ploughed plots, but at the other 3 sites were greater on uncultivated plots, largely because of inadequate grass weed control. Between 11 and 37 spp. were recorded at the various sites, but few occurred at densities in excess of 1/m2. Annual grass weeds, e.g. Alopecurus myosuroides and Poa spp. were more numerous on uncultivated and on shallowly-cultivated plots. Perennial and wind-borne spp. were also more frequent on uncultivated plots. In contrast, annual dicotyledonous spp., in particular Polygonum spp., Anagallis arvensis and Viola arvensis occurred more often on ploughed plots. A few spp., e.g. Tripleurospermum maritimum, responded inconsistently to cultivation, but most spp. were too infrequent to detect a response. Cultivation regime had a marked effect on the seasonal germination patterns of A. myosuroides. More seedlings emerged on uncultivated plots in autumn, but on shallow tine-cultivated plots emergence was greater in spring. Cultivation also influenced the periodicity of germination of P. aviculare, with emergence delayed on uncultivated plots.