Grow your own nitrogen with summer sown serradellas

Date: 05 Nov 2014

Image of growers standing in a field

Key points

  • Sow unprocessed serradella pods between early January and early March
  • Graze the serradella soon after autumn rains and plant anchorage
  • Crop the area in the second year for nitrogen (N) benefits
  • The pasture will regenerate in year three for grazing and soil N
  • Best fit for this system is light soils with a neutral to lower (acidic) pH

Summer sown, hard seeded French serradellas Margurita and Erica are showing potential as key legume inclusions to crop rotations in WA’s medium and high rainfall zones.

Department of Agriculture and Food, Western Australia (DAFWA) trials have found these new generation annual pastures can produce more than 20 kilograms of nitrogen (N) per tonne of dry matter plant biomass grown during the growing season.

For example, in a 400mm or higher rainfall zone, a 6-7 tonne per hectare stand of serradella can leave enough N in the soil to potentially grow two crops in a row with minimal additional applied N.

At a Brookton property last year, a trial of Mace wheat sown after French serradella - with no added N – yielded 5t/ha, had 9.6 per cent grain protein and returned $1360/ha.

Adding 150 kilograms/ha of urea to the wheat in these 2013 trials only marginally increased yields to 5.4t/ha, protein to 11 per cent and returns to $1421/ha – but this strategy had added risks and costs.

After the wheat phase in 2013, the serradella on this property regenerated in autumn 2014 and was grazed - eliminating the need for any supplementary feeding for sheep.

The grower estimates using serradella is saving his cropping enterprise about $100/ha in N input and labour costs, while producing the same crop yields as those from the farm’s traditional subclover/lupin legume system – thus driving up profits.

Summer serradella pod sowing technique

Integral to the successful and cost effective establishment of the French serradellas to cropping rotations is an innovative technique using unscarified/unprocessed seed pods sown into crop stubbles during summer.

This new low-cost system was developed with Grains Research and Development Corporation (GRDC) funding through DAFWA’s Focus Paddock project.

It relies on using the Margurita and Erica varieties that are suited to WA’s acid soils and self-regenerate as a result of long-term breeding and selection efforts by DAFWA research officers Dr Brad Nutt and Dr Angelo Loi.

This feature ensures persistence in a rotational sequence with crops in the long term.

Summer sowing exploits the unique seed dormancy pattern of the serradellas and can help to:

  • Establish pastures cheaper, earlier and more reliably across broadacre areas than traditional annual pasture legumes
  • Avoid the need for de-hulling pods
  • 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
  • Fill an autumn feed gap for livestock
  • Avoid interference with winter crop sowing at the season break.

Getting the best results

The summer sowing technique for hard seeded French serradella has been tested successfully by DAFWA researchers right across the WA grainbelt, over many years and in a range of seasonal conditions.

Tips for good establishment include:

  • If direct drilling pods, this is best done between early January and early March - when high summer temperatures break down the hard seededness
  • Pods can be sown with a crop in a twin seeding system, or top dressed in a paddock which is then sown over with a crop
  • Sow pods, with an appropriate granular inoculant, to a depth of 1cm or less
  • Sow into low weed burden paddocks (after hay is ideal)
  • A stubble paddock without recent use of sulfonyl urea or Clopyralid herbicides is essential.

After the first rains, the seed pods germinate naturally (rates of 70-80 per cent are common) and the pasture plants produce a lot of biomass if conditions are favourable and weed competition is low.

Grazing can start when the serradella reaches the four to five leaf stage and should stop in the spring of the first year to allow seed set and seed bank build-up.

The ideal rotation for the hard seeded serradellas is pasture-crop-pasture and research is showing good pasture regeneration in the third year, post-crop phase.

DAFWA trials have shown wheat yields are higher in crops following summer sown serradella compared to autumn sown, de-hulled and scarified pasture seed in a twin sowing system.

Wheat grown on plots with no legume residue in these trials was consistently lower yielding and produced grain with lower protein levels.

There is a need to knock-down the serradella before sowing a crop and some in-crop control of the legume may be necessary.

Sourcing seed

The serradella pods – when produced on-farm - cost about 50 cents to $1 per kilogram – depending on yield.

At a sowing rate of 20-30kg of pods/ha and cost of inoculating and spreading seed of about $10-15/ha, the $30-45/ha cost of establishment is about half of that for many traditional pasture species.

If bulking up seed, a 1ha plot of serradella pasture can typically produce enough seed to sow 20-40ha.

Other promising pasture legume species

Research in WA and NSW is showing potential for some biserrula (Biserrula pelecinus), gland clover (Trifolium glanduliferum) and bladder clover (Trifolium spumosum) species to be used in a similar way to the summer serradella sowing.

These pasture legumes are undergoing further trials across WA.

More information:

Dr Angelo Loi, DAFWA

08 9368 3907

angelo.loi@agric.wa.gov.au

Dr Brad Nutt, DAFWA

08 9368 3870

bradley.nutt@agric.wa.gov.au

Useful resources:

To see Brookton growers Colin and Anna Butcher and DAFWA’s Angelo Loi discuss growing summer legumes on video go to: www.grdc.com.au/GC113V-Serradella

Pastures Australia: www.grdc.com.au/Research-and-Development/Major-Initiatives/Pastures-Australia

GRDC Project Code DAW00213

Region West