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Methods of analysing competition with special reference to herbage plants:III. Monocultures v. binary mixtures

Published online by Cambridge University Press:  27 March 2009

J. Hill
J. Hill
Affiliation:
Welsh Plant Breeding Station, Aberystwyth
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Summary

A model is presented which considers the effects of competition between pairs of individuals in binary mixtures. Competitive effects are defined in terms of two parameters; a monoculture effect (Mo) which measures competition between like individuals and a mixture effect (Mi) which relates to competition between unlike individuals. If the data from a particular density replacement series conform to the proposed model the ratio of Mi to Mo can be used to determine whether it would be more advantageous to grow a mixture of the two components concerned or a pure stand of the better component. Where appropriate the optimal composition of the mixture may also be estimated. Theoretical considerations suggest that a 50:50 ratio only represents the optimal composition of a mixture when the two components possess a similar expression for the character concerned.

The model has been applied to dry weight data collected over two growing seasons from a glasshouse experiment which contained 5 genotypes of Lolium perenne grown as monocultures and in all 10 binary combinations. Each combination was represented by three mixture proportions. For the majority of these density replacement series the model was satisfactory, with mixture effects tending to be of greater significance during the first of the two growing seasons. Failure of the model was in general due either to a specific form of competition, which maintained the performance of the mixtures at the level of the better monoculture, or to the presence of more complex forms of competition.

The implications of this model for the development of productive herbage mixtures are briefly discussed, whilst the possible effects of invasion by unsown grass species upon the productivity of a pure sward are also outlined.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 83 , Issue 1 , August 1974 , pp. 57 - 65
Copyright
Copyright © Cambridge University Press 1974

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References

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