Germination and Establishment of Themeda triandra (Kangaroo Grass) as Affected by Soil and Seed Characteristics

Abstract

The seed supply of Themeda triandra, syn. T. australis (kangaroo grass), for revegetation purposes may always be limited given the biological constraints on its production. It is important, therefore, that available seed be used efficiently by maximising germination and establishment. In two glasshouse experiments, we investigated the effects of various soil and seed factors and their interactions on germination and establishment of seeds sown on the soil surface and at depth. Maximum germination was achieved by either de-awning seeds and burying them manually at 1 cm depth or by sowing awned seeds on the soil surface in the vicinity of cracks or stones which allowed up to 96% of the seeds to bury themselves by natural means. Diurnal fluctuations in relative humidity of only 30% caused the 4-6 cm long geniculate awns to twist hygroscopically, thereby propelling the seeds along the soil surface and increasing their chances of becoming buried in favourable or 'safe' microsites for germination. A bitumen-coated straw mulch improved germination of de-awned seeds by maintaining high moisture content in the top 2 cm of soil, but inhibited the movement of awned seeds along the soil surface and their entry into safe microsites for germination. The data are discussed in terms of maximising germination and seedling establishment of Themeda, determining the most appropriate seed harvesting and cleaning methods, and selecting sowing methods which are most likely to be effective.