Growth dynamics in relay-cropped cereals in relation to weed competition: a greenhouse experiment

A greenhouse experiment was conducted to reveal whether it is possible to favour winter wheat by reducing the seed rate of spring barley in a relay-cropping system. Since crops sown at low seed rates may be less tolerant to high weed pressure the study also included weed competition. The experimental design was additive, the density of winter wheat being held constant while spring barley density was increased from 167 to 544 plants m(-2). At four successive harvest times, the growth of the crops and weed was followed until barley maturity. The wheat plants remained at a vegetative stage during the study period. Seed rate of barley influenced both barley and wheat biomass less in the presence of weed than in the absence. Weed competition reduced wheat biomass significantly only at the lowest seed rate. The presence of weed also reduced barley biomass. The reduction decreased with increased seed rate. In weed-free stands, seed rate influenced barley biomass less and had no significant effect on barley grain yield, which was on average 772 g m(-2). By contrast, in the presence of weed, barley grain yield increased from 242 to 646 g m(-2) with increased plant density. The relative weight decrease per individual plant in response to barley seed rate and weed competition did not differ between wheat and barley, suggesting that wheat and barley responded equally to treatments. It is concluded that wheat performance is favoured by reduced barley seed rate. However, low seed rate will reduce barley grain yield if the weed pressure is high, while wheat may be less sensitive to the weed situation.