Graduate Thesis Or Dissertation
 

Evaluation of dry-weight-rank and microscopic point techniques for seasonal botanical analysis of two pasture mixtures

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3t945v254

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  • This study was undertaken to evaluate the dry-weight-rank and microscopic point methods for determining botanical composition on perennial ryegrass (Lolium perenne L.) - subclover (Trifolium subterraneum L.) and tall fescue (Festuca arundinacea Schreb.) - subclover pasture mixtures throughout a grazing season. Botanical composition was determined on a monthly basis from April through August, in the field and on three component mixtures in the laboratory. The dry-weight-rank method was modified for use on five different species compositions artifically composited for each pasture mixture. The microscopic point technique was applied to the same samples with first the forage in whole form, then chopped for a second determination. The data were subjected to analysis of variance, linear regression, and correlation, Results show estimations of the microscopic point method on the whole forage were different from those on chopped forage. The ratios of weight to point change because of a change in thickness, amount, and cover of plant parts in the sampling, tray through the season. The greatest differences in all estimations of the components corresponded to the greatest change in the dry matter percentages. Weight per point by the microscopic point method before correction were more accurate in the overall application than were the laboratory dry-weight-rank estimations after correction. The laboratory dry-weight-rank technique is not sensitive to true differences and the overall accuracy is poor without proportional ranking. Without proportional ranking the dry-weight-rank method is only accurate when ratios of the species within the mixture approximate the ratios of the multipliers. Dry weight percentages can be predicted accurately by the microscopic point method within the range of composition levels studied. Different equations are necessary for chopped forage samples. The dry-weight-rank method is not acceptable without considering proportional ranks and may not estimate within ± 5% of the actual dry weight percentages when any one component falls below 60% of the mixture.
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