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, the size and composition of the seed bank were compared 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. The rate of breakdown of hardseed and the loss of high temperature dormancy was also studied in the same genotypes under conditions of alternating temperature in controlled environment cabinets. In terms of the size of the total seed bank, the sub. clover cultivar with the highest level of hardseed (Dalkeith) was the most successful genotype studied. This was the result of slower rates of hardseed breakdown compared to the other sub. clover cultivars, and better seed production compared to the two murex medic lines. Losses of seed from the seed bank were substantial, and were not all accounted for by germinated seedlings or grazing over summer. The sub. clover cultivars Junee and Seaton Park had the highest levels of high temperature embryo dormancy and the lowest proportion of seedlings germinating over summer. The level of sub. clover hardseed breakdown in the field corresponded well with the 60/15�C laboratory estimates of hardseed breakdown, even though soil surface temperatures over summer at Forbes were rarely in the range of 60/15�C.

The effect of temperature on germination of the annual pasture legumes Trifolium balansae and T. resupinaturn was investigated. Seed of T. resupinatum lines SA 12240, SA 14433 (from South Australia), C1Z1Res-B, CPI (Commonwealth Plant Introduction number) 026202-3, CPI 026205-2, CPI 027376-2, SA 14433 (from Western Australia), SA 18904, SA 18922, SA 19851 and CPI 045887-2 and cvv. Kyambro and Maral and T. balansae cv. Paradana and lines CPI 045856-1, CPI 045856-4 and AZ 2326 was germinated at 10, 15, 20, 25, 30 and 35�C. T. subterraneum cv. Junee was included for comparison. It was found that germination in all lines except Maral was reduced at 35�C, whereas at 30�C germination was reduced significantly in all lines except Maral, ClZlRes-B, CPI 026202-3, CPI 026205-2, CPI 027376-2, SA 19851 and CPI 045887-2. Germination at 35OC in T. resupinaturn was related to thousand seed weight with the equation: Germination = -31.19+92-39 thousand seed weight (r2 = 0.76). In order to determine the mechanism responsible for the failure of seed to germinate at temperatures above 25�C, seed of T. resupinatum lines SA 12240 and SA 14433 and Maral and T. balansae cv. Paradana was allowed to germinate at temperatures of 25, 30, 35, 40, 45 and 50�C for 8 h, 1, 2, 5 and 10 days after which they were placed at 15� C for 10 days. It was found that temperatures in the 30-40�C temperature range inhibited germination in all lines except Maral, but the same seed germinated readily when placed at 15�C. This seed was considered to possess an enforced high-temperature dormancy. Seed of all lines exposed to 45 and 50�C for longer than 8 h died, but at 8 h final germination was unaffected. It was concluded that high-temperature dormancy could play a role in preventing seed from germinating in the case of a false break. It was proposed that lines should be screened for high-temperature dormancy.

Murex medic (Medicago murex Willd.) seedling recruitment is more sensitive to soil water at the time of emergence than subterranean clover (Trifolium subterraneum L.). Murex medic pods normally lay on the soil surface. Shallow burial of pods may be beneficial when soil moisture is marginal for germination and emergence. In addition, the tightly coiled structure of murex medic pods may also act as a barrier to water uptake by the seed. Two methods of burying murex medic pods were investigated in the field: (i) trampling by sheep hooves through summer grazing; and (ii) through light cultivation in autumn. A glasshouse experiment was also conducted to examine the interaction between the length of time that the soil stays moist and pod burial for CD26 and CD53 murex medic and Dalkeith, Junee, Seaton Park and Woogenellup subterranean clover. In the glasshouse, pod burial was important for the attainment of maximum emergence in all genotypes when soil water was limiting. However, pod structure did not appear to have a limiting role in germination and emergence in murex medic. When tested in the field, pod burial by sheep trampling through summer grazing improved emergence in CD26, possibly because the smaller more open pod was more easily trampled than that of CD53. Summer grazing in CD53 and Dalkeith and autumn cultivation in all genotypes did not improve emergence; possible reasons for this are discussed so to is the role of murex medic in ley farming systems in eastern Australia.

A field experiment was established at Forbes in central-west N.S.W. to investigate the hypothesis that the pattern and efficiency of water use varies between genotypes of both (Trifolium subtewaneum) and murex medic (Medicago murex), and that this would affect the success of these genotypes in this environment. To test this hypothesis the productivity of two lines of M. murex (CD26 and CD53) and four cultivars of T. subtewaneum (Seaton Park and Woogenellup, and two recently released cultivars, Junee and Dalkeith) were compared. Genotypes were grown both with and without irrigation and soil water was monitored for the duration of the field experiment (1987-1989). Seed production in cv. Dalkeith was higher than in all other genotypes when grown with or without irrigation, and would thus be less inclined to suffer from annual legume decline than the other genotypes studied. Seed yield was very sensitive to small changes in available soil water, especially in sub. .clover cv. Junee, where water shortage over a short period during burr formation resulted in marked yield reductions. Murex medic seed yield was negatively correlated with water use. Seed size was the yield component most affected by available soil water in all sub. clover genotypes except cv. Dalkeith, where plant number was most highly correlated with seed yield. Implications for the persistence of annual legumes and the role of water use models are discussed.

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 (Di) appears to have the greatest influence on dry matter production over the growing season.