COMMON NAME 

Yellow serradella

Pubescent, multi-branched annual  with stems  to 50 cm, procumbent to decumbent. Leaves imparipinnate, finely serrated with 9–18 pairs of lanceolate leaflets and a single terminal leaflet, up to l cm long, and greener than those of pink serradella . Deep rooting, more so than subterranean clover  and pink serradella. Inflorescences are umbels of 1–5 yellow flowers with leafy bracts borne on long axillary stems jutting out from the leaves. Seeds, the majority of which are hard, develop in hard curved pods  with 5–8 constricted segments, each containing a yellow seed, oblong and flattened.  Number of seeds  kg^-1: 100 000 (hulled or podded), 350 000 (dehulled). Average 1000-seed weight: 10.0 g (hulled), 2.9 g (dehulled).

DISTRIBUTION

Grown as an annual  in countries surrounding the Mediterranean. Introduced to southern Australia, where it is grown as a cool-season annual, though only on a small fraction of the potential area to which it is climatically suited (Hill, 1996; Hill and Donald, 1998).

CHARACTERISTICS

Growth  Adapted to regions with a Mediterranean-type climate and to warm, temperate areas. Requires annual rainfall of at least 325 mm. Deep rooted. Suited to non-calcareous soils and to sandy and gritty soils. Tolerant of high soil acidity. Less tolerant of heavy soils than pink serradella. Thrives best under high soil fertility and adequate water supply from autumn to spring, but withstands low soil fertility better than other annual forage legumes in Australia (Clark, 1983). On light, acid soils its P requirement is less than that of subterranean clover (Bolland, 1991), while it tolerates a low soil K status better than subterranean clover (Gladstones and McKeown, 1977).

Its life cycle is geared to escape summer drought, though moderately tolerant to drought. Seeds germinate in autumn following summer dormancy and the onset of autumn rainfall. It has moderate seedling growth vigour. Peak yields  are in spring and the sward dries off during summer. Late-flowering types require more rainfall than early-flowering types during the autumn to spring growth period in order to encourage seed production. Moderately cold tolerant under Australian conditions. Poor to moderate tolerance of waterlogging.

Ability to spread naturally Regenerates each year after summer dormancy from the soil seed bank  formed in late winter–early spring, though the high proportion of hard seed gives protection against false summer or early autumn breaks, i.e. premature germination after rainfall episodes that are then followed by drought. The hard seed also enables a soil seed bank to be built up for the long term and so it has a longer stand life than pink serradella.

Compatibility in mixture Blends of yellow serradella  cultivars with differing characteristics can be used according to the soil and climatic features of the regions where sown. It may be sown with pink serradella  in mixture (Clark, 1986) and with subterranean clover , rose clover  or biserrula. It is compatible with warm season grasses, e.g. Rhodes grass  (Chloris gayana), lovegrass  (Eragrostis curvula ) and buffel grass  (Cenchrus ciliaris ) (Freebairn and Gardner, 2001).

Nitrogen fixation Rhizobial inoculation with an effective Rhizobium is required when yellow serradella  is sown onto land for the first time, though not on land that has previously borne lupins (Lupinus spp.). Strains of Bradyrhizobium spp. have been selected for effectiveness in specific regions (Ballard, 1996). Following seed inoculation, rhizosphere colonization and plant and root nodulation  were better with hulled than unhulled seed and the inoculant persisted as a reservoir of inoculum for annually regenerating yellow serradella  (Bowman et al., 1995).

BREEDING

Chromosome number 2n=2x=14. Breeding objectives include improved vigour of growth and resistance to pests.

Cultivars A number of Australian cultivars have been released that range from early to late maturing, prostrate to upright growth habit, moderate to high tolerance of soil acidity and Al toxicity, and ease of break-up of the segmented pods  (Freebairn and Gardner, 2001). Cultivars commercialized include Avila, Charano, Elgara, Eneabba, King, Madeira, Paros, Pitman, Santorini, Tauro and Uniserra.

Seed production Seed is harvested by conventional seed crop harvesting  and threshing equipment before pod segmentation and shedding. Some varieties can be harvested with cereal harvesting machinery. Freebairn and Gardner (2001) note 60 percent of pods  harvested at first field crop stage, 20 percent at second windrow stage and 20 percent at a third vacuum harvesting stage. Seed yields are variable, e.g. a range of 390 to 900 kg ha^-1 of clean dehulled seed has been reported for cv. Paros (Anon., 1990). Hulled seed yields reported include 300 kg ha^-1 from dryland conditions and 2500 kg ha^-1 from an irrigated crop (Freebairn and Gardner, 2001).

AGRONOMY

Establishment A well cultivated, uniform and firm seed bed  is required for good results when first establishing conventionally. It is normally drilled into a conventionally prepared seed bed. Sown at 10–15 mm depth with a firm soil cover, and generally sown in later summer to early autumn, when there is sufficient soil moisture to ensure good seed germination. Seed rates are 1–3 kg ha^-1 for dehulled seed and 5–10 kg ha^-1 for hulled seed. Aerial seeding may also be practised.

A mechanical seed dehuller has been developed, which improved the germination from an initial 20 percent to 50 percent (Sanders, 1996). Soaking seeds  in concentrated sulphuric acid (98 percent ) for 30 minutes reduced hard seed from 88 percent to l percent (Fu et al., 1996). Burial of pods  accelerates breakdown of hard seed (Revell, Taylor and Cocks, 1998, 1999) due to a requirement for darkness (Taylor and Revell, 1999).

Nutrient requirements Adequate soil fertility is required to ensure satisfactory yields.

Weeds Its ability to compete with weeds  is moderate during early establishment, but it is competitive later as dense canopy develops.

Pests The climbing or native budworm (Heliothis punctigera) can severely reduce seed production. It is generally tolerant to aphids (Aphis spp.) and to lucerne  flea (Sminthurus viridus). Can be susceptible to red-legged earth mite (Halotydeus destructor) at seedling cotyledon stage.

Diseases Generally good resistance to disease, although with some sensitivity to root rots.

Forage production DM yields  of 3–6 t ha^-1 are cited for New South Wales, Australia (Freebairn and Gardner, 2001). In Western Australia, spring forage DM yields ranged from 3.1 to 5.2 t ha^-1, compared with 4.3–5.8 t ha^-1 for pink serradella  (Loi et al., 2000).

NUTRITIVE VALUE

Rich in crude protein  (CP) concentration and with high digestibility. Nutritive value declines with advancing plant maturity and corresponding reduction in leaf : stem ratio. Values reported include CP of 292 g kg^-1 DM (early vegetative stage) and 217 g kg^-1 DM (full bloom stage); low levels of acid detergent fibre (ADF), at 188–231 g kg^-1 DM, and high levels of metabolizable energy (ME), at 11.2–12.0 MJ kg^-1 DM (Anon., 1989a). It is highly acceptable forage for different classes of livestock, whether grazed or fed as silage, with low bloat risk.

UTILIZATION

Grazing management More suited to infrequent rather than frequent defoliation , and so rotational  grazing  is the best option (Frame, Charlton and Laidlaw, 1998). In the spring, a balance has to be struck between efficient forage utilization and a rest period to allow the plants to flower and set seed, but it can be grazed hard until flowering. Dried-out summer forage should be well grazed to facilitate sward regeneration from the seed bank in autumn.

Conservation management Suitable for conservation as hay or silage.

MAIN ATTRIBUTES

It is adapted to a range of dry environmental and edaphic conditions, particularly acid soils. Ability to self-regenerate annually in autumn from seed pods  shed before summer drought. High nutritive value. High degree of resistance to diseases and pests. Hard-seeded and can persist through a cereal cropping phase.

MAIN SHORTCOMINGS

Sward density and forage yield are variable from year to year, partly because of dependence on amount of seed produced for annual  regeneration. There are currently limited options for broad-leaved weed control  with herbicides.

MAIN REFERENCE

Freebairn and Gardner (2001); Frame, Charlton and Laidlaw (1998).

LINKS

• Agnote NSW Agriculture on O. compressus L.
• Paper on “Imbibition and germination of yellow serradella seeds"
• Paper on “Breaking dormancy in yellow serradella seed”
• CLIMA data on pasture cultivars including yellow serradella
• Queensland DPI notes on yellow serradella
• Tasmania PFCAC: Approved cultivars including yellow serradella
• Serradella - a pasture legume for deep acid soils