Abstract:
A relatively simple deterministic model is presented which predicts the long-term changes in plant densities of subterranean clover strains when grown as binary mixtures in continuously grazed swards. The model combines life-cycle parameters, based on measurements in monocultures, together with the 'k' parameters of the de Wit replacement series model for mixtures during the seed production phase. Field data, for the most part under grazing conditions, were collected from the CSIRO Experiment Station at Bakers Hill, W.A. The principal strain pairs of clover were Dwalganup/Daliak, Yarloop/ Seaton Park and Seaton Park/Midland B. Beginning with 50/50 mixtures, our results indicate that Daliak dominates the first mixture fairly rapidly; that Seaton Park dominates the second mixture, but more slowly; and that the two strains in the Seaton Park/Midland B mixture may coexist for long periods (up to c. 100 years). Results for some other mixtures, viz. Dwalganup/Northam, Daliak/ Dinninup and Geraldton/Dinninup are presented. The effects of intervention of a cereal crop in the pasture system are considered briefly. The findings are discussed in relation to density dependence, constant v. variable environments, importance of seed characters, genetic changes, and also long-term coexistence.