Some factors affecting change in botanical composition in a ryegrass-white clover pasture under continuous grazing

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Abstract
Differences in botanical composition of swards obtained from a sowing of Lolium perenne, Lolium perenne × L. multifiorum, and Trifolium repens following six years of management under three different grazing treatments were studied. The swards that developed under Lax and Moderate grazing systems were virtually pure stands of the sown species, namely, the ryegrasses and white clover. In the swards that developed under Continuous close grazing, marked ingress of Agrostis tenuis, Poa spp., Oxalis corniculata, Hydrocotyle moschata, Sagina procumbens, and Taraxacum officinale occurred. Observations on plant distribution pattern and the association between species were made in the swards of the Continuous close grazing treatment. At two scales of sampling A. tenuis showed marked negative associations with L. perenne and with Poa spp., whereas ryegrass and Poa spp. were positively associated with T. repens. Sampling along transects and mapping of species in an area of the Continuously close-grazed sward showed that the main species of the association were concentrated in different parts. The possible influence of soil nitrogen and soil moisture content on this pattern was investigated, and it was demonstrated that A. tenuis had a well-defined association with low soil nitrogen and high soil moisture sites. Collected information suggests that the death of Manawa ryegrass individuals in the sown mixture hastened the ingress of A. tenuis in the Continuously close-grazed sward. Practical implications of these results are discussed.