Long-term dynamics of weeds in grassland-crop rotations. 2. Effects of the mode of exploitation of the meadow, mowing or grazing.

The objective of the study was to evaluate the effect of the mode of exploitation of the grassland, mowing or grazing, on the dynamics of weeds in grassland-crop rotations. The study was conducted in a long-term experimental design. The experimental treatments included 6-year grasslands in rotation with a 3-year crop succession (corn, winter wheat, winter barley) and permanent grasslands. Each of the 2 grassland types was subjected to either a mowing or a rotational grazing regime by dairy cows. The results show that the abundance and diversity of weed species was greater in the grazed grasslands than in the mowed grasslands. As a result, in the first crop year following the grassland phase of the grassland-crop rotation, weed abundance was greater when the grassland had been grazed than when it had been mowed. This effect diminished in the second year of cropping. Thus, a grazed grassland appears to be less effective than a mowed grassland in reducing weed abundance in the annual cropping phases of grass-crop rotations.