Vetch shows promise as WA pasture option

Free-nitrogen farming with a portfolio of pastures

Grower Stories
Clint Butler examines a rhizobia-coated vetch trial on his Narembeen, Western Australia, property. PHOTO Evan Collis

Clint Butler examines a rhizobia-coated vetch trial on his Narembeen, Western Australia, property. PHOTO Evan Collis

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WA eastern wheatbelt trials point to vetch as a viable alternative to medic pastures.

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SNAPSHOT

  • Growers: Clint, Kim and Sue Butler
  • Farm name: Bonview Pastoral Company
  • Location: Narembeen, Western Australia
  • Business enterprise: 70 per cent cropping, 30 per cent pasture/livestock, 1300 breeding ewes
  • Property size: 4000 hectares
  • Soil types: Sandy loams (acidic) through to heavy soils (alkaline)
  • Soil Ph: 5.5 (lighter soils) to 8.75 (heavy soils)

Early results from trials in Western Australia's eastern wheatbelt suggest vetch could be a viable alternative to typical medic pastures in fine-textured, heavy, alkaline soils.

In this low-rainfall, low-input farming environment, growers are on the hunt for alternative pasture legumes that have the dual benefit of providing valuable livestock nutrition, plus measurable benefits for subsequent cereal crops.

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To date, WA growers with heavy-textured, alkaline soils have been limited to medic pastures in a mixed farming operation.

But results from the trials - managed by Murdoch University's Centre for Rhizobium Studies, with GRDC investment - are illustrating vetch could be a viable option in the region if managed correctly.

The WA trials are on the property of Clint, Kim and Sue Butler, at Narembeen, where medics have been a long-term part of their rotation on heavy soils.

Clint says his medic pasture is struggling to thrive in lower-rainfall years, with a shallow root system reducing both the plant's biomass production as well as its potential as a quality feed source.

Vetch can be harvested with a conventional harvester while medic clovers can't, which adds to the appeal of vetch in the region.

With 20 per cent of his property made up of heavy-textured soils, finding a legume that is the right fit for the system has become a priority for the business.

Low inputs, low cost

For the Butlers, farming in such a tough environment means any pasture crop in the rotation must provide the entire business with a range of benefits for more than just one year, not least of which is nitrogen fixation for future wheat and barley crops.

"In this environment, we need to improve our profitability through a reduction in costs, which means we are always looking at ways to reduce inputs," Clint says.

"Producing cash crops with minimal applied nitrogen is the future for our business."

The Butlers have planted a range of different pasture legumes over the past decade, including serradella, biserrula, subclovers and medics.

They are convinced serradella, in particular, is having a significant impact on the production and profitability of their subsequent wheat and barley crops, because of the nitrogen fixation in the pasture phase.

In this environment, we need to improve our profitability through a reduction in costs, which means we are always looking at ways to reduce inputs. - Western Australian grower Clint Butler

But Clint says hard-seeded serradellas are better suited to his sandy, more acidic soils, while vetch could prove a winner for his heavy alkaline country.

"We had a barley crop in 2019 that followed serradella the previous year, which only received seven units of applied nitrogen, and it yielded 1.8 tonnes per hectare, with 12 to 13 per cent protein, after just 120 millimetres of growing-season rainfall," he says.

"We were very happy with this result given the seasonal conditions."

In fact, Clint says anywhere on the property where there was a legume in 2018, the 2019 crops not only looked better all season, but yielded higher as well.

"We know this system works for us, but we now need to find a way to replicate this on the heavy soils - and vetch could possibly be the answer for us," he says.

Several trials on the Butlers' property are considering a range of different pasture legume crops, with one specific trial comparing woolly pod vetch (cv. RM4) with medics, fallow and barley.

The trials

Five treatments were as follows:

  • March-sown vetch;
  • May-sown vetch;
  • medic pasture;
  • chemical fallow; and
  • barley

Soil testing was undertaken prior to seeding, assessing nematode and other pathogen numbers, soil nitrogen values and soil moisture values.

Murdoch University research officer Rob Harrison believes the early sown vetch is showing very real promise on these heavy soils.

"What our group is always trying to achieve is a portfolio of pastures on demand - allowing growers to make decisions with a range of options as the season unfolds," Mr Harrison says.

"So far, early sown vetch is proving to be a possible productive alternative to the traditional medic pastures that have perhaps run their course in this region in terms of disease control and biomass production."

In WA, vetch has predominantly been grown in the south-east coastal regions, where longer-season varieties fit into higher-rainfall mixed crop and livestock operations.

Trialling the crop in the low-rainfall eastern wheatbelt was a gamble, Mr Harrison says, but one that paid off after 25mm of rainfall in early April on warm soil.

"But after that first rainfall event, there was almost no rain until the very end of May, and the crop was under severe stress. Despite this huge moisture gap, the crop came back and ended up producing 1t/ha more biomass than the later-sown crop," he says.

Given these biomass results, the early sown vetch has the potential to be a viable option on these soils types.

"The early sown vetch achieved 1t/ha more biomass in a variable season, indicating this early sowing technique is more robust than later sowing and medics," Mr Harrison says.

Weeds

Being a vigorous crop with significant biomass, the early sown vetch proved excellent competition for weeds.

"The later-sown vetch didn't have the opportunity to establish its canopy and wasn't able to out-compete the weeds as well as the early sown crop," Mr Harrison says.

Vetch can tolerate most grass selectives and can be grazed in-season, further reducing the weed burden.

Mr Harrison says the early sown treatment was planted at depths of about five centimetres to chase moisture, keep the rhizobia alive and to aid in strong early establishment.

"You wouldn't sow deeper than 2cm for small-seeded pasture legumes like serradella, but vetch seed is much larger and can handle the deeper sowing," he says.

Vetch has a low percentage of hard seeds, but there was a very low seed mortality rate despite the deep sowing rates.

"Vetch appears to be a very resilient plant that can handle long dry periods, high alkalinity and heavy soils," Mr Harrison says.

Integrative weed management techniques using vetch as a phase crop include grazing, silage, hay cutting and brown manuring (spray-topping).

Vetch appears to be a very resilient plant that can handle long dry periods, high alkalinity and heavy soils. - Murdoch University research officer Rob Harrison

Feed source

Mr Harrison says growers in the region have shown a lot of interest in having an alternative legume option for their rotations.

"At all the fields days we held, growers were very keen to see how it could be used for conserved fodder in hay and silage production because they are particularly worried about losing their spring feed in these changing climatic conditions," he says.

The nutritional value of vetch

Vetch is a legume and therefore the plant biomass contains high nutritional value, particularly as it can reach crude protein levels of about 30 per cent.

It is similar to other pulses in terms of fodder quality and has big advantages in a mixed farming system, where both livestock and soil nutrition can benefit.

But the seeds from the woolly pod vetch variety can be toxic to sheep. So if it is to be grazed in-season, or cut for hay or silage, that needs to occur before the plant sets its seeds.

To retain seed, vetch can be harvested with a standard machine, which reduces costs, compared to the suction harvest method required by medic pastures.

"Any pasture legume in a low-rainfall rotation must have very low input costs to be of value to the entire business," Mr Harrison says.

Rhizobia

Vetch should be inoculated with peat slurry containing rhizobia prior to planting and, as part of the WA trials, new strains of rhizobia were used and monitored throughout the trial.

Dr Ron Yates, project leader of pasture agronomy and rhizobiology at Murdoch University, is managing a wide-ranging research project searching for new rhizobia strains suitable for legumes planted into Australian soils.

While his focus has been on rhizobia for acidic soils, he says the new strains appear to be effective in these alkaline soils as well.

"What we now know is these new strains are very robust and while the focus of this specific project has been on the effectiveness of these strains in acidic soils, we are also wanting to get a better understanding of how they work in all types of soils, which is why they have been included in these trials," he says.

"In particular, we are investigating how long the rhizobia can survive on the seed once it has been slurry inoculated.

"The recommendation is that, once inoculated, the seeds must be planted almost immediately. But we know that might not be realistic out in the paddock and growers might go 12 hours before planting seed."

Dr Yates says the testing has been rigorous and thorough to ensure these new strains can handle eastern wheatbelt conditions.

Nitrogen

Clint Butler says vetch has potential on heavy alkaline country at his Narembeen, WA, property. PHOTO Evan Collis

Clint Butler says vetch has potential on heavy alkaline country at his Narembeen, WA, property. PHOTO Evan Collis

The true value of a pasture legume in a cash crop dominant rotation is the nitrogen fixation that is unlocked in subsequent crops.

Dr Yates says the goal of any effective pasture legume is to allow for a free-nitrogen farming system.

"The beauty of the plant residue left from legumes is that the breakdown and release of plant available nitrogen in future crops is activated by moisture," he says.

"Bacteria in the soil that breaks the residue down and turns this into available nitrogen has a strong correlation to soil moisture availability."

Conversely, less rainfall will mean less nitrogen mineralisation.

For Clint Butler, 2019 was an example of how useful pasture legumes can be in a system that operates on minimal moisture, particularly late in the season.

"Applying too much nitrogen in a very dry year can create small grain, and high screenings, and we saw the difference in the crops that followed a legume and had lower rates of nitrogen applied," Clint says.

Future research

In 2020, all the treatments will be planted to wheat, with varying rates of nitrogen to ascertain how much nitrogen is needed on the subsequent cereal, if any at all, for optimum yield and quality.

GRDC Research Code UMU1805-001RMX

More information: Rob Harrison, r.harrision@murdoch.edu.au

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