The effect of infestation by Lolium rigidum Gaud. (annual ryegrass) on the yield of wheat

The effect of ryegrass infestation on the grain yield of wheat was examined and related to a yield analysis equation. Up to the two-leaf stage, apparently through competition for nitrogen, the presence of ryegrass at quite a low density (450 plants per m2) reduced the capacity of wheat plants to produce laterals. Neither the later removal of ryegrass nor the addition of nitrogen overcame this setback. In fact, the results suggest that nitrogen addition would result in a further loss in yield, and that this would increase with increasing density of ryegrass. However, the presence of ryegrass up to the two-leaf stage did not affect grain number per head or grain size: such effects were entirely dependent on the presence of ryegrass during the reproductive stage.