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Subterranean clover seedling survival in a summer rainfall environment

R.D. FitzGerald

NSW Agriculture, Agricultural Research and Advisory Station, Glen Innes NSW 2370

Rainfall on the northern tablelands and slopes of NSW north of latitude 30°S is summer dominant with highest monthly averages in December and January and lowest in April and May. Subterranean clover, Trifolium subterraneum, germinating in summer is vulnerable to desiccation (1) and seed reserves may be diminished by widespread germinations after summer rains. However, cultivars with comparatively low levels of hard seed (e.g. Woogenellup) persist in this region above 500 m altitude. This suggests that either the proportion of hard seeds persisting under grass cover is sufficient for a viable plant population (2), or that seedlings from summer germinations are able to survive the summer/autumn conditions. An experiment was conducted at Emmaville, NSW (29.5°S), to determine the fate of subterranean clover seedlings germinating in the January to May period.

Methods

Plots of three cultivars (Junee, Woogenellup, Mt Barker; three replications) were established in autumn 1985. In spring 1990, these cultivars were contributing 81%, 70% and 61% respectively of total herbage yield. During the summer/autumn of 1991 there were four distinct germinations of subterranean clover. Seedlings from these germinations were observed until their death or until commencement of reliable moisture conditions in May.

Results and discussion

The proportion of seedlings surviving till the commencement of reliable moisture conditions was highest from germinations in January and declined with germinations in subsequent months until May (Table 1).

Table 1. Duration of survival in days of subterranean clover seedlings from four germination events over summer/autumn. Percent of seedlings surviving until May is shown in parentheses.

Germination in the higher rainfall months, presumably from relatively permeable seeds, was conducive to better seedling survival than when germination was delayed until later when rains are less frequent. Woogenellup seedlings survived the later germinations better than the smaller-seeded cultivars.

References

Hagon, M.W. 1974. Aust. J. Exp. Agric. Anim. Husb. 14, 57-64.

Lodge, G.M., Murison, R.D. and Heap, E.W. 1990. Aust. J. Agric. Res. 41, 941-955.

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