PLANT-POPULATION DYNAMICS IN SUBTERRANEAN CLOVER AND MUREX MEDIC SWARDS .2. PLANT-POPULATION DENSITY

It is possible that the use of harder-seeded varieties of sub. clover (Trifolium subterraneum) and the recently domesticated murex medic (Medicago murex) may improve annual legume persistence in pasture leys. To determine the mechanisms of production and persistence in these two species, plant population density changes in single seed (sprayed) and naturally regenerating (unsprayed) swards were monitored in four varieties of sub. clover and two lines of murex medic over a three year period at Forbes in central-west N.S.W. Seedling recruitment was very sensitive to soil water and temperature at the time of germination and emergence, particularly in murex medic. Murex recruitment under irrigation was at least four times greater than without irrigation on a germinable seed basis. Irrigation of sub. clover swards did not improve recruitment to the same extent as it did in murex medic. Even the soft seeded cultivars (Junee, Seaton Park and Woogenellup) can regenerate from residual seed in the year following a year in which no seed was set, although there are qualifications for Woogenellup. Plant population density (D) declined over the growing season, despite the specific effects of environment and management; initial plant population density (D(i)) appears to have the greatest influence on dry matter production over the growing season.