Graduate Thesis Or Dissertation
 

Evaluation of species composition by four methods on two perennial grass pastures (Festuca arundinacae Schreb. and Lolium perenne L.) grazed lightly and heavily in western Oregon

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  • The present study was undertaken to evaluate the seasonal botanical composition of two grass pastures, tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.). Botanical composition was determined by four methods: dry-weight-rank, weight-estimate, hand separation, and the constituent differential, with cattle and sheep grazing at two intensities. The pastures were sampled eight times during the growing season (March 23-July 8), taking 50, 25, 5, and 5 observations with the dry-weight-rank, weight-estimate, hand separation, and constituent differential methods, respectively, using a 2.4-square-foot circular plot. New sets of multipliers had to be determined for the dry-weight-rank method. Three different ways of grouping the data were tested. Best results were obtained in both pastures when all the data were grouped from all grazing treatments, because no significant differences were detected among the experimental errors in the analyses of variance used to test data arrangements. Consequently, the use of only one set of multipliers was found to be more practical. The same ways of grouping the data were used to calculate the regression equations to give the most accurate correction for the weight-estimate method. Uncorrected data were also tested. It was determined that best results were obtained in the fescue pastures when all the data were grouped within each of the grazing treatments. In the ryegrass pastures, on the other hand, all data collected in each sampling period was found to be the best arrangement, provided that the number of observations is increased to compensate for greater pasture variability. An analysis of variance was run on the information obtained with each method in both pastures. It was concluded that, in the fescue sections, the methods gave similar results regardless of the kind of livestock, grazing intensity, and sampling period. Units grazed by cattle showed a lower fescue percentage, especially those heavily grazed, than those grazed by sheep; grazing intensity did not affect the trend of the fescue percentages in the mixture which declined as the season progressed. In ryegrass pastures, the ryegrass percentages obtained in each case were influenced by all four treatments: methods, kind of livestock, grazing intensity, and sampling periods. It is apparent from this study that the constituent differential method is the most promising one, and more attention should be directed to it in the future. A study is proposed to explore some of the factors influencing the use of the constituent differential method for determining production and botanical composition on mixed grass-legume pastures.
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