Blue lupins (suited only to NAR)
Blue lupins, also called sandplain lupins are a deep-rooted, self-regenerating annual legume well suited to the infertile sandy soils in the coastal belt of the NAR.
Blue lupins are somewhat maligned, but do have some strengths as they are: a productive legume for infertile sands, have high stubble value as a stock feed over summer, provide nitrogen for companion plants, are tolerant of false breaks and have a lower nutrient requirement than subterranean clover.
However, blue lupins also have a number of limitations including low palatability when green, animal health risks due to alkaloid toxicity when green and the potential for lupinosis in summer following rainfall. Blue lupins can also exacerbate non-wetting problems of sandy soils, shade out other pasture species if left dense and ungrazed, are susceptible to frosts and waterlogging and very susceptible to anthracnose. The seed pods shatter on maturity, so harvestability is an issue.
Overall, the use of blue lupins is best restricted to very infertile sands in the NAR where serradella does not grow well.
Perennial legume options
A number of perennial legumes have been evaluated in field trials or by producers, but in general their potential role as companion legumes is limited:
- Strawberry clover is a waterlogging tolerant perennial clover normally grown in temperate, high rainfall environments – it is only an option in niche environments where there is sub-surface fresh water within the root zone.
- Lucerne is marginally adapted to the climate in the NAR and poorly suited to the sandy soils predominantly used for growing sub-tropical grasses.
- Lotononis is a sub-tropical perennial legume adapted to sandy soils, but the very small seed size makes establishment problematic as the emerging cotyledons are often buried by sand in-fill.
- Tropical perennial legumes (eg. siratro, burgundy bean, stylo) – all require the combination of good soil moisture and warm to high temperatures for growth as they are more ‘tropical’ than the warm season grasses. These conditions are only experienced following summer rainfall, so biomass production and therefore nitrogen fixation is generally very low.
Methods of establishment
The main two methods for establishing annual legumes into perennial grass pastures are summer sowing or conventional seeding after the break of season.
Summer sowing refers to sowing pod (or unscarified seed) in late summer–early autumn. Companion annual legume options suitable for summer sowing include:
- Margurita (PBR) and Erica French serradella (pod)
- Avila yellow serradella (pod) – higher rainfall (>600mm) areas only.
Refer to guidelines for summer sowing serradella into perennial grass pastures; Highly productive sub-tropical grass—serradella pastures.
Conventional sowing refers to sowing seed after the break of season following full weed control and if required suppression of the sub-tropical grass through grazing or the use of herbicide. All of the annual legume options can be sown from seed including the hard-seeded yellow serradella varieties which are unsuitable for summer sowing.
Inoculant
For new sowings it is recommended to inoculate with the correct Rhizobia: i.e. Group C for subterranean clover and Group S for serradella. Options include the lime pelleting of seed using a peat-based or freeze-dried inoculant or drilling a granular inoculant with the seed (refer to Inoculating pasture legumes).
Re-establishing subterranean clover from an existing seed bank
A high proportion of kikuyu pastures on the SC have a viable subterranean clover seed bank, yet frequently contain a low clover content, usually as a result of competition from kikuyu, insect pests or low soil fertility. Methods to increase legume content in these swards, without re-seeding include:
- Apply sufficient grazing pressure to kikuyu particularly in autumn, before the break of season, to reduce thatch and allow clover seedlings to establish.
- Control RLEM - The new cultivars, Rosabrook (PBR), Narrikup (PBR), Bindoon (PBR), Tammin (PBR) and Forbes (PBR) have increased cotyledon resistance to RLEM. However, resistance is not absolute and pesticides should be used at seeding and also in regenerating pastures when RLEM densities are high.
- Improve soil fertility (phosphorus, potassium) − based on soil test results.
- Suppress kikuyu using a grass selective herbicide when the clover seedlings are establishing.
Acknowledgements
This research was co-funded by the Department of Primary Industries and Regional Development (DPIRD), Meat and Livestock Australia (MLA) and the Grains Research and Development Corporation (GRDC) EverCrop project. We acknowledge Dr Brad Nutt (Murdoch University) for information on the seed dynamics of serradella and Dr Phil Nichols for information on subterranean clover.
(PBR) denotes pasture cultivars that are protected under Plant Breeder's Rights legislation. Unauthorised propagation of seed for commercial purposes or sale of these cultivars is an infringement under section 53 of the Plant Breeders Rights Act 1994 and is subject to prosecution.