Summer serradella emerging as a viable legume option
Summer-sown hard-seeded French serradella (Ornithopus sativus) varieties have potential to revolutionise the legume phase of crop rotations in Western Australia’s medium and high-rainfall zones, according to researchers.
These self-regenerating pasture legumes are the result of long-term breeding and selection by Department of Agriculture and Food, Western Australia (DAFWA), researchers Dr Brad Nutt and Dr Angelo Loi.
Initially developed for their suitability to WA’s acid soils, which limit the productivity of traditional pasture species, the hard-seeded serradellas are now being used in a low-cost summer-sowing system that exploits their unique seed dormancy to provide delayed and valuable autumn feed for livestock plus nitrogen for crops.
This system involves sowing unprocessed pods from the serradella varieties Margurita and Erica. They offer opportunities to:
- establish pastures cheaper, earlier and more reliably than traditional annual pasture legumes;
- fast-track the transition between crops and pastures;
- improve pasture biomass production;
- achieve good seed-set;
- achieve high N fixation in the first year of the pasture phase; and
- avoid interference with winter crop sowing at the season break.
The GRDC has funded research into this summer serradella pod-sowing technique through the DAFWA Focus Paddock and Grain & Graze projects.
Dr Loi says the keys to its success are the cost efficiency and reliability of sowing Margurita and/or Erica serradella across large areas. It is estimated that one hectare of serradella pasture can produce enough seed for a 20 to 40ha sowing.
When produced on-farm the serradella pods cost about 40 to 50 cents per kilogram. At a sowing rate of 25 to 30kg of pods per hectare and costs of inoculating and spreading seed of about $10 to $15/ha, the $25 to $30/ha establishment cost is about half that of many traditional pasture species.
Dr Loi says when sown in WA between early January and early March, high summer temperatures break down the serradella’s hard seed.
“It is vital to sow the serradella pods into a low-weed-burden paddock by the end of summer to exploit this, achieve 70 to 80 per cent germination and optimise plant density at the season break,” he says.
“After the first rains, the seed pods germinate naturally. The plants can produce a lot of biomass if conditions are favourable and they will compete well with weeds.
“Grazing can start when the pasture plants reach the four to five leaf stage and should stop in the spring of the first year to allow seed-set and seedbank build-up.”
Dr Loi says the ideal rotation for the hard-seeded serradellas is pasture-crop-pasture and research is showing good pasture regeneration in the third year after a crop phase.
He says trials have shown wheat yields are higher in crops following summer-sown serradella compared with autumn-sown, de-hulled and scarified pasture seed in a twin sowing system (where pasture and crop seed are sown at the same time).
“The hard-seeded serradellas can produce more than 20kg of nitrogen per tonne of dry matter plant biomass grown during the growing season,” he says.
“So, in a 400-millimetre or higher rainfall zone, a six to seven tonne/ha stand of serradella will leave enough nitrogen in the soil to grow two crops in a row.”
There is a need to knock down the serradella before the cropping phase and some in-crop control of the legume may be necessary.
Dr Loi says the summer-sowing technique for hard-seeded French serradella has been tested with good success right across the WA grainbelt over many years and in a range of seasonal conditions.
He says research in WA and NSW is also showing potential for some biserrula (Biserrula pelecinus), gland clover (Trifolium glanduliferum) and bladder clover (Trifolium spumosum) species to be used in a similar way and these pasture legumes will undergo further trials in WA in coming years.
Dr Angelo Loi, DAFWA
0429 378 279
Dr Brad Nutt, DAFWA
08 9368 3870
More information: see Pasture phase delivers free nitrogen and fodder in Ground Cover Supplement Grain & Graze (with this issue)
GRDC Project Code DAW00213