Companion legume options for sub-tropical grasses in southern Western Australia

Page last updated: Friday, 6 October 2017 - 3:53pm

Please note: This content may be out of date and is currently under review.

Serradella

There are two main species of serradella grown in WA; yellow serradella and French serradella. They can both produce an extended period of green feed in spring compared to most annual legumes due to their indeterminant growth habit and deep root system.

The strengths of serradella include: adaptation to deep infertile sandy soils, acid soil tolerance (pHCa>4.0), high palatability to stock with excellent nutritive value and no major anti-nutritional properties, good tolerance to RLEM and aphids and the ability to harvest seed on-farm.

Weaknesses include susceptibility to native budworm during seed production, some susceptibility to lucerne flea, limited broadleaf weed control options with selective herbicides and unsuitable for soils with an alkaline pH.

Results from field trials and commercial paddocks in the NAR demonstrate that serradella can be a highly persistent and productive companion legume for sub-tropical grasses – refer to Highly productive sub-tropical grass—serradella pastures.

Seed bank dynamics

The persistence of annual pasture species relies on regeneration from the seed bank, so an understanding of seed bank dynamics, in particular hard-seed breakdown and the subsequent germination patterns is useful.

Hard-seed breakdown (or seed softening) occurs in response to large diurnal changes in soil temperature over the summer–early autumn period; e.g. high temperatures 40-60°C during the day followed by mild temperatures at night. However, there are not only differences in the proportion of seed softening between species, but also in the timing of hard-seed softening.

For example, in subterranean clover almost all the hard-seed breakdown for that year has occurred by mid-March and the seed is then ready to germinate. Yellow serradella and hard-seeded French serradella behave quite differently, while the ‘Cadiz (Plant Breeder's Rights - PBR)’ and ‘Eliza (PBR)’ varieties of French serradella are nearly 100% soft-seeded (i.e. all of the seed is ready to germinate once the plant senesces).

‘Margurita (PBR)’ and ‘Erica’ are hard-seeded French serradella varieties, with about 40-60% of seed softening each year. Seed softening occurs gradually over an extended period from late summer through to late autumn. Erica is not widely used and there is limited availability of seed.

The commercial varieties of yellow serradella developed for use in cropping systems - i.e. Santorini, Charano, Yelbini (PBR) - have a high proportion of hard-seed which will persist for more than one year in the soil, with <30% of the seed softening in any one year. As a result, regeneration of these yellow serradella varieties will be poor in the year after sowing due to the high hard-seed content.

There are also differences between varieties as to when the ‘softened’ seed will germinate. The commercial varieties of yellow serradella developed for cropping systems have varying degrees of delayed germination after the onset of moist soil conditions, while hard-seeded French serradella germinates within the first 10 days providing the soil moisture is adequate (e.g. seed not sitting in a pocket of non-wetting sand). Santorini yellow serradella has the most protracted germination pattern which extends out to 40 days.

Table 2 Summary of key characteristics of French and yellow serradella varieties including days to flowering when grown in Perth and likely persistence in medium-term as companion species for perennial grasses – assuming good management (X – very low to √√√ good)
Species / variety Days to flowering Rainfall zone (mm) Annual
hard-seed breakdown
Suitability summer sowing Protracted germination pattern Likely persistence in medium-term
Cadiz1, Eliza2
(French serradella)
1101, 902 350−5001
300−4002
NA
(100% soft seeded)
No No X
Margurita, Erica
(French serradella)
~115 450−650 40-60% Yes No √√
Avila
(Yellow serradella)
120 600-750 40-60% Yes No √√√
Santorini, Charano, Yelbini
(Yellow serradella)
80−110* 350-600 <30% No Yes** √√√

1,2 link each cultivar to flowering time and target rainfall zone
*Days to flowering when grown in Perth are Santorini 105-110 days; Charano ~95 days and Yelbini ~80 days
**Varies with variety, Santorini has the most protracted germination (up to 40 days)
PBR varieties include Cadiz, Eliza, Margurita and Yelbini.

Yellow and French serradella are somewhat similar species, but yellow serradella is a more robust plant and more likely to persist in the medium and long-term. Hard-seeded French serradella is a more ‘showy’ plant and can give good production in the first couple of years, but there are questions about its persistence in the medium-term (Table 2). In pasture-cropping rotations regular re-seeding is expected, but with good management perennial grasses are productive in the long-term (>15 years) and ideally the companion legume would also persist in the medium- to long-term.

decorative
Serradella sown into a kikuyu pasture in Esperance
decorative
Perennial grasses with blue lupin stubble

Contact information

Geoff Moore
+61 (0)8 9368 3293
Paul Sanford
+61 (0)8 9892 8475