The effect of defoliation and sward density on the growth of some annual pasture species

Abstract

The comparative production from pure and mixed swards of capeweed (Arctotheca calendula), subterranean clover (Trifolium subterraneum), and annual ryegrass (Lolium rigidum) grown in containers was measured over a 12-week period. Densities of one to 64 plants dm-2, and clipping frequencies of two- and four-weekly intervals and no defoliation were combined factorially. Plant survival decreased as density rose for all swards. More frequent defoliation increased the survival of capeweed and clover in mixed swards and capeweed in pure swards. In both pure and mixed swards, capeweed produced the most herbage at low densities, but this advantage was not maintained at the highest density in undefoliated swards when ryegrass was the most productive. Increased defoliation reduced root weights. The treatments only affected the root : shoot ratios of capeweed grown at high densities-clipping at four-week intervals gave higher ratios. In the mixed swards, capeweed content declined and clover and ryegrass content increased as density was increased. Capeweed content was little altered by defoliation, but subterranean clover increased and ryegrass decreased with more frequent defoliation.