Population dynamics of Trifolium balansae and T. resupinatum in self-regenerating pastures. I. Seed and plant densities and dry matter yield.
In a field trial near Forbes, central-west New South Wales, Trifolium balansae cv. Paradana and T. resupinatum lines SA 12240 and SA 14433 were sown as monospecific swards with and without irrigation; the field site had a red-brown earth soil. Seed bank and plant population densities and herbage yield were measured over a 3-year period. Seed density in the seed bank was highest just after seed production and lowest during the growing season. Up to 65% (average of c. 40%) of seed present in the seed bank before summer disappeared during the mainly dry summer months between seed set and autumn regeneration. Another 31% decrease in seed density occurred during regeneration. Seed impermeability was highest (95%) just after seed production and during the growing season and lowest (78-87%) just before regeneration. Seedling density was very high (up to 10 000 plants per m2) after regeneration, but more than 90% of plants died during the growing season. In 1988 plant density during the growing season was two to three times higher than in 1989 and 1990. Total dry matter yield did not differ significantly between the lines tested, but Paradana plots had a significantly higher clover content than SA 12240 and SA 14433 plots, ranging from 2253 to 1068 kg per ha. Paradana was better suited to the experimental environment than was either T. resupinatum line; differences in plant size and subsequent seed production were the major factors contributing to the successful persistence of Paradana.