Methods of analysing competition with special reference to herbage plants: I. Establishment

Abstract

A diallel arrangement, which incorporated the essential features of the de Wit density replacement series, was employed to study the effects of competition amongst five genotypes of perennial ryegrass (Lolium perenne). Of the five genotypes concerned two were derived from S. 24, two were collected from natural populations in South Wales, while the remaining genotype originated from S. 23. These five genotypes were grown as monocultures and in all ten binary combinations. Within each combination there were three mixture proportions, namely 75:25, 50:50 and 25:75. All mixtures and monocultures were represented by two boxes, one of which was cut at 3-week intervals (frequent cutting) the other being cut at 6-week intervals (infrequent cutting). At each cut all plants within the appropriate mixtures and monocultures were harvested individually and their dry weight recorded.The results obtained over the first 18 weeks of the experiment (i.e. the first three complete growing periods) establish that competition is occurring in nine of the ten binary combinations. Within these nine combinations competition may be classified into one of three groups: first, it may be compensatory, in which the gains and losses incurred by the two components counterbalance; secondly, it may be positive complete complementation, where the advantage gained by the stronger component is such that the mixture performance matches that of the better monoculture, and thirdly, it may be positive over-complementation, where the yield of the better monoculture is surpassed by the mixture. Further tests disclose that a long-leaved S. 24 genotype is the strongest competitor, while a short-leaved, prostrate, indigenous genotype proves to be by far the weakest competitor.Estimates of the equilibrium proportions for each genotype combination suggest that most combinations are expected to become monocultures of the strongest component, with only the combination between the long-leaved indigenous and longleaved S. 23 genotypes remaining a mixture at equilibrium. None of these equilibria coincides with the proportions required to achieve maximum productivity from a particular combination. The results are considered in relation to the known characteristics of these five perennial ryegrass genotypes, while the. wider agronomic implications are also discussed.conditions of competitive stress the individual organisms or components are reacting towards Competition arises where two or more organisms each other's presence in order to secure for themseek a common resource whose supply falls below selves a sufficient share of the environmental their combined demands (Donald, 1963). Hence resources. From an agronomic standpoint such competition may be regarded as a medium through reactions are of considerable importance because which the environment regulates the balance of the impact they can have on the composition between the components of a mixture. Under and yield of herbage mixtures, regardless of the * Present address: Laboratory of Industrial Crops, degree of ...

EXPERIMENTAL STUDIES ON THE DISTRIBUTION OF THE SEXES OF MERCURIALIS PERENNIS L.

“…Examination of the variances of the data for the sexes showed that the variances were independent. The data for total yield were compared in a replacement diagram (Harper, 1977;Hill and Shimamoto, 1973) and were expressed as relative yield totals (Hall, 1974).…”

Environmental advantages of binary mixtures of Trifolium incarnatum and Lolium multiflorum over individual pure stands

“…This variation in the results can be explained by ecological concepts of niche differentiation. Higher productivity of mixtures relative to that of pure stands occurs if the between-species competition is low, and complementarity between species promotes better use of natural resources (Hill and Shimamoto 1973, Snaydon 1991, Möller et al 2008. The yield advantage of binary mixtures over pure stands can be expected when suitable components in the mixture are brought together for specific growing conditions.…”

Analysis of competitive ability among genotypes of perennial ryegrass

“…From five perennial ryegrass genotypes (clones) used in a previous experiment (Hill and Shimamoto, 1973), three (B, C and E) were chosen for this investigation. Marked morphological differences exist between these three genotypes in that B is short-leaved, densely tillering and with a very prostrate growth habit, whereas both C and E have larger leaves, are less densely tillering and have erect growth habits.…”