Choice of seed treatment

The ancillary structures of native grass seed are such that many of them will not flow through conventional sowing equipment. Recently specialised planters have been developed to sow chaffy, fluffy seeds, but seed distribution is often variable and result in uneven seeding rates. Fluffy seed can be processed to remove some of the surrounding structures and/or appendages and so improve their capacity to flow evenly through seeders. For some species at least this can reduce the ability of the grasses to establish in the field as well as adding to the cost of the seed. In addition, seed dormancy of some species is associated with the ancillary structures. There is evidence that 'undressing' seed of some species down to the naked caryopses, while increasing the ease of handling and reducing dormancy, also reduces longevity and consequently shelf life of seed.

There are three main ways that native grass seeds can be sown-as naked caryopses or achenes, as uncontaminated dispersal units or as dispersal units plus other trash including seeds of other species, leaves, stalks and infertile spikelets (Spikelet - Consists of one or more florets and is the basic unit of the inflorescence in grasses). There is evidence that for some species at least establishment success may depend on which form is used for sowing. For example, Bothriochloa, Dichanthium, and Heteropogon have hygroscopic (Hygroscopic - responds (twists or opens) to moisture changes) awns that assist in burying the seed when it gets wet. In other grasses, awns are present, but are not hygroscopic, and assist in the orientation of seed on the soil surface. It has also been suggested that the 'husk' and hairs surrounding the seed play a role in retaining moisture around the caryopsis (Caryopsis - the indehiscent fruit of most grasses with a single seed, the testa (seed coat) of which is fused with the pericarp (outer wall)) during germination.

Dispersal units and trash

Seed harvesting using a brush harvester often collects not only ripe seed and whole inflorescences (Inflorescence - a group of flowers borne on a stem) of the target species but also seed and inflorescences of other species (including weeds) and varying amounts of leaves, stalks and other plant material. If this material is spread on the soil surface, either as harvested or after passing through a chaff cutter to chop up the long stalks, then the ancillary structures of the seeds are usually left undamaged. The seed plus trash can thus be sown on the soil surface without burial. This approach has proved to be the most successful for at least one native grass Themeda triandra (Kangaroo grass), and certainly has potential for others. It is most important when using this approach to adequately sample the collected material and calculate the number of germinable seeds per unit mass so that adequate sowing rates can be calculated and used. This approach complicates collection (and therefore distribution) of unwanted seeds. Removal of weed seeds is difficult from this material.

Uncontaminated dispersal units

Seed processing to obtain uncontaminated dispersal units of some native grasses is difficult and may result in damage to the ancillary structures which assist in locating the individual seeds in favourable microsites. Furthermore, the dispersal units of many species still will not flow easily through conventional sowing equipment. It is important that uncontaminated dispersal units be sown at the appropriate depth for the species (see Species quick reference).

Naked caryopses

The advantage is that the caryopses will flow easily through conventional sowing equipment but it is very difficult to process the seeds of some species to this stage without damage (e.g. Microlaena stipoides and T. triandra). In addition, shelf life may be reduced, as mentioned above.