Grains Research and Development

Date: 10.02.2015

Pastures for purpose

Author: Tim Prance (T Prance Rural Consulting)

Take home messages

  • Select pasture that is already commonly sown in your district.
  • Management for dry matter and seed production often overrides cultivar selection. 
  • Check how well your existing pastures are nodulating.
  • Sow new pastures early, using high seeding rates and inoculate with the latest rhizobia strains.
  • Treat your pastures like a crop, take care with insect and weed control and manage grazing to maximise profit from pastures.
  • Have a go!  Try a new cultivar/species and trial a summer sowing cultivar/species.  Try however, a small paddock first, so that the results achieved are a reflection of your environment and not your management. 
  • To assist in evaluation, leave a small area unsown/untreated.

What are the options?

I will focus on legume pastures because of their value for livestock production and contribution to soil nitrogen for crops.

There is no shortage of “you beaut” legume pastures to trial. The list of annuals from the GRDC Pasture Legume Ute guide and a few others from the Australian Seed Federation web site (www.asf.asn.au ; search seed database) are listed here:

  • Sub clover – brachycalycinum e.g. Clare types
  • Sub clover – yanninicum e.g. white seeded Trikkala types
  • Sub clover – subterranean everything else
  • Medics – barrel, strand, disc, hybrid disc, burr, gama, murex, snail, sphere
  • Balansa clover, persian clover
  • Bladder clover, gland clover
  • Biserrula and Serradella -yellow, or french
  • Arrowleaf clover, berseem clover , crimson clover, cupped clover and rose clover
  • Vetch - purple, common, woolly pod
  • Lathyrus
  • Melilotus, (Messina*)
  • Perennials/biennials such as lucerne, sulla, sainfoin, lotus and tedera.

(n.b.* Not yet commercially available)

But I seem to keep coming back to barrel and strand medics, sub clover and lucerne and possibly sulla for SA.

Cultivar selection

Key factors to consider are soil pH (alkaline or acidic), maturity (days to first flowering and minimum growing season) and hard seededness. The GRDC Pasture Legume Ute guide lists hard seededness of all legumes from 0 (none) to 10 (100%) depending on the level of hard seed remaining at the break.

Lucerne

Lucerne is a good option for a short term pasture phase (2-4 years) especially if you want to clean up grassy weeds using different herbicide groups to those used for cereals or pulses. Lucerne is also a good pasture option to fill the feed gap between the end of the growing season and when stubbles become available, especially for weaner lambs. There is excellent local lucerne breeding program, and a wide range of varieties from which to choose one suited for your farm.  Inter-row sowing lucerne with the last cereal crop in a rotation means lucerne is ready to go the following year making establishment costs much lower.

Sulla

Sulla is worth trialling on red brown earth soils as it provides extremely high yields once established and additional livestock benefits due to high levels of condensed tannins along with anthelminthic properties.

Annual legumes

It is important to choose a cultivar to suit your farming system and rotation. Avoid selecting a variety that matures too early, as you want the pasture to be green for as long as possible.  Use also a range of maturities to take account of seasonal variations.

If you want good regeneration in the year following establishment, then don’t select a cultivar with a hard seed rating of 8 or 9. Alternatively if you are concerned about legume contamination in your crops, then select a softer seeded cultivar.  Examples of some ratings are as follows:

  • Barrel medics such as Sultan, Jester, Caliph and Parabinga have a hard seed rating of 8-9.
  • Strand medics such as Angel, Herald or Harbinger have a hard seed rating of 7.5 – 8.5.
  • Burr medics such as Cavalier, 7-8 rating and Scimitar, rating 6.5 – 7.5.
  • Sub clovers. Hard seeded cultivars have a rating of 5 -6 and most are 3-4.
  • Casbah biserrula has a rating of 8-9 *.
  • Cadiz French serradella is 1, while Margurita is 6
  • Bladder clover is 6

*In NSW Belinda Hackney reports she has never had biserrula not regenerate successfully in the second season, as opposed to WA where it is very rare to see it regenerate in second year following sowing. This observation indicates that there are considerable differences in hard seed break down rates in NSW compared to WA, and possibly also in hard seed formation (Belinda Hackney pers. comm.).

However, it was noted that pasture management should be focussed on producing as much seed as possible in the first year stands (Belinda Hackney pers. comm.). In addition, if the new legume species has a high seed count per kilogram (e.g. biserrula, 1 000 000 seeds/kg compared to sub clover, 330 000 seeds/kg) there does not need to be a high percentage of seed softened in the second year to have a high number of germinable seed per square metre.

Of course, if you are concerned about legume contamination in your crops, then hard seededness is not high on your priority list.

Hard seed production is influenced by season. Long spring equates to more hard seeds and short spring equates to less hard seeds. This is opposite to what you might think, but the plants are telling us something! 

Hard seed breakdown is also influenced by extremes of hot and cold.  Extreme weather equates to greater breakdown. Burying seeds (cultivation) equates to less breakdown. Removing dry residues over the summer/autumn period equates to more breakdown. 

Hard seed breakdown is probably linear. Assuming you have 400 kg/ha of seed reserves and 80% are hard (rating 8), you will have 320 kg/ha left at the end of the season.  Next year there will be 80% x 320 kg/ha remaining (i.e. 256 kg/ha), then after third year 205 kg/ha, etc.  However, with time more seeds get buried, so the rate of breakdown will reduce, and of course every summer is different with regards to temperature.

Establishment of annual legumes

High seeding rate

Keep seeding rate on the high side.  Ten kg/ha for medics/sub clovers and legumes with similar seed sizes, five kg/ha for small seeded legumes (balansa and persian) and >20 kg/ha for serradella pods.

Sow early (before the break) and cover the seed. Drilling into stubbles in early April is perfect.

 In NSW and WA they are successfully sowing hard seeded French serradella (Margurita), as well as biserulla, bladder and gland clovers in February/March.  The practice of very early sowing is well suited to species (e.g. serradella, biserrula, bladder and gland clovers) that have a high seed content.  A number of WA/NSW farmers are sowing unscarified seed (biserrula, bladder clover, gland clover) or pods (French serradella). Early sowing is essential to enable hard seeds to soften, especially those still in pods.  

Early sowing also greatly increases the amount of dry matter produced in early winter, provided you let the newly germinating pasture to accumulate 3-4 true leaves before grazing.  Don’t sow into a stubble with a history of sulphonyl urea/Lontrel ® herbicides, unless you are sowing a sulphonyl-urea tolerant medic.  For more information please read the Issue 113 Groundcover (www.grdc.com.au/GC113-Serradella) or the 2014 November-December Ground Cover supplement.

Effective inoculation

There is no point in having a legume if it doesn’t produce nodules. If you want to know how effective your “native” rhizobia are, collect four or five soil cores from a paddock and place in a few pots, plant some ethanol washed legume seed in each pot then look at nodulation after a few weeks, by carefully washing out the roots.  Don’t pull the plants out!

If in any doubt, ensure the legume seed is treated with the correct (and latest) rhizobia strain. If the seed is pre-treated (coated), ensure it is stored under cool, dry conditions preferably for no longer than one or two months before it germinates.

GRDC has some good inoculation guides (www.grdc.com.au/GRDC-BPG-InoculatingLegumes ; www.grdc.com.au/GRDC-Booklet-InoculatingLegumes ).  Make sure you read them, and keep up-to-date as there is a lot of misinformation out there.

In NSW, farmers are drilling in Alosca® granules with serradella pods/unscarified biserrula, bladder or gland clovers in February and obtaining good nodulation.

Evidence has been found of improved nodulation and production from inoculated medics at three trial sites in the SA Mallee, even though the paddocks had a long medic history.  Consequently, it is recommended that inoculated medics are used (Source: Jake Howie and Ross Ballard, www.grdc.com.au/GC102-NewMedicsReviveMalleeRotation ).

WA research shows re-inoculation of ‘old’ sub clover pastures substantially increases production and N-fixation, and I am also aware of similar results in east Gippsland.  It therefore may be worthwhile to inoculate any new pasture legume sowings.

A suggestion would be to do some demo strips to enable you to draw your own conclusions.  This would involve:

  • Bare seed inoculate using gum sticker a maximum of 1-2 weeks before seeding.
  • Bare seed sow with Alosca® granules.
  • Use coated seed e.g. Seed Distributors, Heritage seeds, etc.
  • Include a small area of bare seed with no treatment as a control demo strip.

Don’t forget to use the same variety and seed source for each treatment.

A couple of months after your legume pastures germinate dig up a few plants and check for nodules.  Dig carefully and wash the roots. If you pull a plant up you will strip the nodules off.

Management of legume pastures

Treat your pastures like a crop.

The aim is to get as much green dry matter produced as quickly as possible, then to maximise seed production in spring. To achieve this:

  • Delay grazing until legumes have 3-4 true leaves.  Depending on seed density, this can double winter pasture growth rates compared to grazing as soon as there is a “pick” of green leaf.
  • Check newly germinating pastures for insects, especially around the edges of paddocks. Keep an eye on aerial seeding pastures, such as serradella, for heliothis grubs in spring.
  • Use grazing to manage your pastures and weeds. Grazing need not be complicated, but should be consistent. Follow the match box rule (Figure 1).
Figure 1. Match box rule.

Figure 1. Match box rule.

  • Do not crash graze, especially during flowering. There is nothing wrong however, with grazing a pasture during flowering, as long as the grazing pressure is consistent before and after flowering.

You can employ an agronomist to manage your weeds and insects, but you can also employ a few sheep which will also help manage your weeds and insects and make you money.

One dry sheep equivalent (DSE) removes one kg green dry matter/ha/day, so a pasture growing at 20 kg/ha/day should have a grazing pressure of 20 DSE/ha to keep pace with pasture growth.  Use Table 1 to determine how many animals this equates to.

Table 1. DSE equivalents.

Livestock class

DSE equivalent

1 dry ewe

1.2 - 1.5

1 ewe and lamb

3.5

1 weaner lamb

2.0

1 cow and calf

17.0

During summer, adjust grazing according to your pasture cultivar, soil type, topography and crop rotation.

Legume pastures regenerate best if most of the surface residues are removed by mid- autumn. In addition, small seeded legumes, and those with pods such as serradella and biserrula, regenerate better if sheep digest the pods over summer/autumn, because the seeds pass through their digestive system. In contrast, seed of larger seeded legumes such as sub clover and medics is readily digested by livestock and regeneration can be adversely impacted if sheep are allowed to eat sub clover and medic burrs during summer.

Remember, seed production is the key to successful regeneration. If you have 400 kg/ha seed reserves x 80% hard seeds = 80 kg/ha potential germination x 260,000 seeds/kg x 70% seedling mortality = 1460 plants/m2 = good stand!  Some clover/medic paddocks have 1000 kg/ha seed reserves which equates to a really productive paddock especially in winter.

Conclusions

  • Use what is already commonly sown in your district, but focus on management for dry matter and seed production. 
  • Aim to treat your pastures like a crop.
  • Check how well your existing pastures are nodulating.
  • Try a new cultivar/species and trial a summer sowing cultivar/species.  Try however, first a 10 ha paddock and learn how to manage for best establishment, nodulation, productivity and regeneration and don’t forget to leave a strip untreated as a control.  Once you have mastered the small area, you can then go onto sow larger sized paddocks.

Contact details

Tim Prance, PO Box 1439 Victor Harbor SA 5211
0427 812 655
t.prance@bigpond.net.au
@PranceTim