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The fate of new sub clover cultivars in old Mt. Barker pastures in Tasmania

P.M. Evans, J.A. Carpenter and E.J. Hall

Department of Agriculture, Mt. Pleasant Laboratories, Tasmania 7249

New cultivars of sub clover will normally be sown into soils that contain a substantial seed bank of older cultivars, mainly Mt. Barker (1). It is important, therefore, to determine if these new cultivars can become the dominant clover when their initial seed numbers are less than those already present in the soil.

Methods

A cultivar evaluation trial with 15 commercial sub clovers was sown in Autumn 1986 at Gretna (4240' S, 14651" E; 550 mm annual rainfall). The site was an old pasture which had been cropped. Plots were drilled with a cone seeder at a rate of 20 kg/ha (replicated four times) on an area which had just been sown with perennial ryegrass at a rate of 6 kg/ha. Plots were grazed after each herbage assessment and during the summer. Seed yield was measured after the first and third seasons by taking four 10 cm diameter soil cores to a depth of 5 cm in each replicate. Cores were washed and cleaned and white seed separated from black in the sub-species yanninicum plots. Seed from the sub-species subterraneum were grown-on to determine varietal composition.

Results and discussion

At the end of the first season, the average Mt. Barker contamination across all white-seeded plots averaged 114 kg/ha. After three years the total sub clover seed bank increased for all cultivars except Enfield (Table 1). Trikkala most effectively reduced the total Mt. Barker seed bank followed by Larisa. Enfield, though suppressing Mt. Barker, also lost some of the seed bank from the first year in the process. Karridale, and to a lesser degree Meteora, increased their seed bank without severely depressing the Mt. Barker seed reserves (Table 1). Since the Karridale plots had the highest clover DM production of 1988 and Enfield the second highest, it is suggested that an introduced cultivar can be successful by either severely restricting an existing one or by developing into a very productive mixture.

Table 1. Total seed yield with their Mt. Barker component at the end of the first and third growing seasons

Our results agree with those of Hotton and Curnow (2), where Enfield and Karridale succeeded in preventing a build up of Mt. Barker seed. Trikkala and Larisa reduced the Mt. Barker population at Gretna but not at Kyneton, perhaps our climatic or soil conditions were more favourable to the yanninicum sub-species than those of the Victorian experiment.

1. Evans, P.M. (1989). Proc. 5th Aust. Agr. Conf.

2. Hotton, G.B. and Curnow, B.C. (1987). Proc. 4th Aust. Agr. Conf., 164.

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