The effect of clipping frequency on the competitive interaction between two perennial grass species.

The effect of clipping frequency on competition between Lolium perenne and Agrostis tenuis was investigated. The yield of clippings of both species increased and then declined during the 12-week period of the experiment, but the clip yield of Lolium was always significantly greater than that of Agrostis. Lolium was clearly the better competitor in unclipped controls. The proportion of the biomass contributed to the mixture by Agrostis increased as the interval between clips decreased. Tiller production was unaffected by increased clipping frequency in Lolium but was increased in Agrostis. Total yield was much more drastically reduced by frequent clipping in Lolium than in Agrostis, where yield was practically unaffected by wide variations in clipping frequency.These results are in agreement with the field distributions of the two species. They also suggest that differences in height and response to clipping are likely to confound any attempt to monitor the progress of competition experiments by measuring the yield of clippings.