The influence of density and nitrogen on the outcome of competition between two annual pasture grasses (Hordeum leporinum Link and Lolium rigidum Gaud.)

Abstract

The hypothesis that the outcome of competition between Hordeum leporinum Link and Lolium rigidum Gaud. depended predominantly on the density of Hordeum was tested in two experiments. In the first experiment it was postulated that increasing the density of Hordeum increased its competitive ability; in the second experiment the interaction between soil nitrogen and density was studied. Under the conditions of the first experiment the hypothesis was shown to be true. The competitive ability of Hordeum was closely related to its density, and neither the density of Lolium nor the total density had a significant effect. Hordeum was most competitive when its density was highest. The second experiment showed that soil nitrogen was an important modifying factor. At low nitrogen Hordeum was the successful competitor, but its competitive ability decreased with increase in its density. At high nitrogen Lolium became the successful competitor, although the effect of Hordeum density was similar to that in experiment 1. At the lower levels of nitrogen the density of Lolium also affected the outcome of competition, but its effect was never as great as that of the density of Hordeum. The results are explained in terms of the original hypothesis and of the different abilities of the two species to absorb soil nitrogen.