Sowing serradellas

Increased interest in our region

Tablelands Telegraph – May 2021

Clare Edwards – Senior Land Services Officer, Pastures

This autumn, I have received a number of enquiries about sowing serradella in our region. There has been an increased interest in serradella, and a few recent research projects have investigated the potential of these hard-seeded legumes. However, serradella is not new – I was monitoring these legumes in trials back in 1997 in the Armidale district. What may be sparking the renewed interest is some of the attributes of these legumes in variable climates, landscapes and soils.

Serradella is an introduced, deep-rooted, self-regenerating, cool season annual. There are two main species of serradellas – yellow serradella (Ornithopus compressus) and French or pink serradella (Ornithopus sativus). They are suited to light acid soils but do not tolerate waterlogging and have low potential to cause bloat due to the presence of tannins.

Both species have performed well (especially in the first year) in my Central Tablelands hard-seeded legume demonstration plots over the last seven years.

Serradella produces seed aerially and has an indeterminate flowering time meaning it will continue to produce seed. In dry conditions, they may flower less, but are better able to produce seed under such conditions as they are much deeper-rooted (>1.6 m) compared to subterranean clover (60-90 cm).

I have seen some good stands of yellow serradella in light sandy soils around the Mudgee-Rylstone area which have persisted over a number of years and through recent drought conditions.

There are a few points to consider when making a decision on which species and particular variety to use.

Firstly, consider whether yellow or French serradella suit your situation. Yellow serradella tends to have higher levels of hard seed and is more prostrate in its growth habit meaning it is more tolerant of grazing. Additionally, yellow serradella has good tolerance of native budworm which can cause significant reductions in seed production of French serradella. Yellow serradella varieties generally vary from 50->80% hard seed. Some varieties with very high hard seed content also have unusual and delayed hard seed breakdown patterns.

French serradella tends to have a more upright growth habit and hard seed levels range from 0-60%. Choose a variety with maturity that suits your area; mid- to late-season maturing varieties are better on the tablelands while mid-season will suit the slopes areas. Choose a more medium- or soft-seeded variety if you are looking for second-year production. These may be more suited to short-term production pastures or to provide opportunities for improved production in the initial years of a perennial pasture.

Most of the varieties have a high tolerance of soil aluminium with some varieties tolerant to red legged earthmite and aphids. De-hulled, scarified seed is preferred if a stand is required immediately.

When using serradella, it is essential to understand the need to inoculate the seed with the correct rhizobia strain (Group S).

In recent legume surveys across the Central Tablelands, it was noted that serradella was prolific in its nodulation. They often scored higher than sub clover and showed substantially more nodules on their root systems. This is likely attributable to better adaptation of both the serradella plant and its rhizobia to acidic soils compared to sub clover. Lastly, check seed availability; in some years there is adequate supply but in other years it can be limited.

Recent studies of serradellas have investigated their persistence by looking at maturity dates or flowering times (Boschma et al 2019). Maturity dates are important for long-term survivability as serradellas are an annual and hence rely on establishing a good seed bank.

Secondly, maturity dates or flowering dates are important when considering the potential for frost damage to pod formation or, at the other end of the season, for completion of mature pods before hot, dry conditions set in. There may be a balance between those years when germination occurs early (giving good seasonal production) and the potential for poor seed production due to early flowering during frost periods.

Other current research work is investigating the differences between sub clover and serradella. For example, serradellas have been reported to have lower requirements for soil phosphorus and they have long root systems with greater root-per-gram root dry mass than sub-clover. The serradellas also exhibit longer root hairs, meaning they have a greater surface area to extract nutrients.

However, check that serradella is compatible to the conditions in which you wish to grow it, that is, well drained soils that do not get waterlogged. It will not be able express efficiency if it is grown in an unsuitable soil.

Management of serradella is just as important as with sub clovers. Seasonal conditions that produce large amounts of herbage mass over summer will need to be managed to allow the serradella to germinate in early autumn. To ensure an adequate seed bank, it is suggested that stands be managed to allow a seeding event every few years.

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