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Sample size and sampling intensity in relation to the precision of small-plot herbage sward trials

Published online by Cambridge University Press:  27 March 2009

C. A. Foster  and
C. E. Wright
C. A. Foster
Affiliation:
Plant Breeding Station, Loughgall, Co. Armagh, Northern Ireland
C. E. Wright
Affiliation:
Plant Breeding Station, Loughgall, Co. Armagh, Northern Ireland
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Summery

Three sampling experiments were conducted to examine the effect of sample size and sampling intensity on the precision of dry-matter content and botanical composition estimates of perennial rye-grass-white clover herbage. One of these experiments examined the between-sample variability of these attributes and of dry-matter yield in relation to other sources of experimental error in a small-plot sward trial. The sample sizes examined were 800 g, 400 g, 200 g, 100 g, 50 g and 25 g green weight. In general the accuracy of dry-matter content and botanical composition estimates decreased with decreasing sample size. The between-sample variabilities of 25 g and 50g samples were high in relation to their between-plot variabilities. Single 100 g samples provided reasonably good estimates of these attributes and of dry-matter yield, but single 200 g samples provided a more satisfactory margin for error. Samples larger than 200 g appeared to be unnecessary. When weight-for-weight comparisons of single and duplicate samples were made there appeared to be little advantage in duplicate sampling. A theoretical examination of measurement inaccuracies inherent in the techniques used in small-plot sward trialssuggested that variation in plot length measurements in particular may make an undesirable contribution to the variability of such trials. A procedure for the conduct of small-plot trials is recommended. It is concluded that, where plot size and replication are limited, further improvement in the precision of such trials will not be readily attainable.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 70 , Issue 1 , February 1968 , pp. 19 - 27
Copyright
Copyright © Cambridge University Press 1968

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