Snapshot

• Growers: Brett and Nicole Broad; Ian and Diane Broad
• Location: North Mingenew, Western Australia
• Property size: 8800 hectares (6500ha arable)
• Enterprises: Mixed cropping and livestock
• Livestock: 1000 ewes and 120 cows
• Soil types: Mainly deep yellow sand
• Soil Ph: Between 4 and 5

Findings from a broad-scale research project are challenging the notion that pasture legumes are only of value in a mixed cropping/livestock enterprise.

Early results from trials in Western Australia suggest certain pasture legumes can achieve adequate nitrogen fixation and mineralisation in nutrient-poor, sandy soils, to provide for a subsequent cereal crop - without the need for additional applied nitrogen.

Margurita serradella, both summer-sown and autumn-sown, is being compared with subclover pastures and chemical fallows to better understand the benefits of the hard-seeded Mediterranean legume.

While serradella is known for its large plant biomass and feed value for cattle and sheep in a mixed enterprise, researchers are also investigating other benefits from the legume crop, such as provision of crop nitrogen and weed and disease control.

The trials are part of a $20 million Department of Agriculture and Water Resources Rural R&D for Profit project run by Murdoch University. It is working in collaboration with WA's Department of Primary Industries and Regional Development (DPIRD), CSIRO and the Mingenew Irwin Group.

Coordinated by Dr Ron Yates, the project has co-investment from GRDC, Meat and Livestock Australia and Australian Wool Innovation.

The project is focusing on the value of the pasture legume in medium and low-rainfall zones.

Researchers hope a new hard-seeded, short-season serradella variety will be available in future to allow growers in lower-rainfall zones to also see success with serradella in their rotations.

Well-known pasture legume research scientists, including associate professor Dr Brad Nutt and Dr Angelo Loi, are working with other researchers and consultants from across Australia to determine how serradella can work in mixed farming - as well as continuous cropping enterprises - over a range of soil types and rainfall zones.

The scientists believe there is a place for serradella in all grain businesses, with the benefits from the crop lasting for several years.

"Through this project, we are hoping to demonstrate to growers there are clear and long-term economic benefits by taking a paddock out of a continuous cash cropping rotation and planting it to serradella," Dr Loi says.

He says the value to a continuous grain business will come through reduced nitrogen and herbicide applications in subsequent cereal crops, plus a range of other benefits, such as:

• reduced nematodes;
• increased potassium availability; and
• increased organic matter in the soil.

The research

The four-year trials began in 2018 with treatments planted to pasture legumes, a chemical fallow and a cereal control, to be followed in subsequent years by wheat, barley and alternative legume treatments.

Soil testing across the four years will consider nitrogen, pH and other constraints on plant growth, such as weed competition and boron toxicity, plus soil-borne pathogens, such as crown rot and nematodes.

Other measurements throughout the four years will include:

• plant rooting depths;
• weather data;
• other pests and diseases;
• pasture density and plant biomass;
• plant digestibility;
• yield (in the legumes and subsequent cereals); and
• soil moisture profile.

In 2018, five treatments in the two separate trials at Mingenew (northern WA grainbelt) and Ardath (central WA grainbelt) compared:

• summer-sown Margurita serradella (PBR);
• normal (autumn) sown Margurita serradella (PBR);
• subclover;
• chemical fallow; and
• weed control.

An early finding, particularly evident at the Mingenew site, has been the value of summer sowing the serradella to allow for the breakdown of the hard pod over the autumn months.

Results demonstrate the summer-sown serradella achieved vigorous early plant growth because the seeds were ready to germinate immediately on the break of season and, as a result, the total plant biomass produced was triple that of the normal-sown serradella and four times that of the subclover.

Likewise, the resulting total nitrogen produced was closely related to the plant growth, as seen in Figure 1.

Figure 1: Nitrogen production in trials crops.

Dr Loi believes the data produced by this project will go a long way towards convincing grain growers to more accurately assess the nitrogen requirements of their crops grown after serradella.

"Nitrogen applications are an expensive input for growers and if they can take advantage of the nitrogen fixed by vigorous pasture legumes, then their risks are reduced," he says.

He says serradella also appears to bring potassium to the surface to allow for future plant uptake.

Continuous cropping role

Project manager Dr Ron Yates says wheat has been planted on all the treatment plots this year, with different rates of applied nitrogen to assess the benefits of nitrogen fixed by serradella in 2018. Yield and protein will be measured at the end of the season.

In 2020 and 2021, the treatments will include barley, alternative legumes and wheat.

The trials are attempting to understand the holistic benefits of pasture legumes to subsequent cereal crops and whether the change from subclover-dominated pastures to serradella-dominated pastures requires an alteration to the bio-economic modelling of mixed farming.

Table 1: Soil analysis results from May 2019.

Dr Yates says introducing the hard-seeded serradella into a mixed crop and livestock operation makes perfect sense, "what if you don't have livestock?"

His answer, particularly for growers in lower-rainfall regions and who have paddocks that may be difficult or no longer profitable to crop is serradella’s soil regeneration capabilities. The root systems have greater biomass and penetrate deeper than the traditional legumes, allowing the plants to grow later in the season, particularly on less-fertile soils.

Added to this improved weed control it can provide in problem paddocks: "Notwithstanding the competition provided by serradella, particularly in spring, the legume offers a break crop to allow the use of alternative herbicides and strategic spraytopping," he says.

"The legume break also lessens the disease load, with early results indicating that one year of serradella is sufficient to dramatically reduce nematode population numbers.”

One of the project's drivers is to develop a hard-seeded variety of French serradella that is adapted to short seasons, with easy harvestability, allowing growers in low-rainfall regions to plant the crop, and harvest it, using standard equipment.

Heading-up the breeding of this exciting new serradella variety is Murdoch University's associate professor Dr Brad Nutt.

He says the hard pod that encases the Margurita types of serradella seed breaks down after sowing when it is exposed temperature changes.

"What this means is the seed can be harvested in the previous season with standard machines, and doesn't need cleaning before planting, which is very different to subclover and medic cultivars," Dr Nutt says.

Margurita experience

Mingenew grower Paul Kelly has a continuous cropping enterprise that now includes the summer-sown Margurita.

Paul didn't take long to be convinced of the value of the hard-seeded serradella on his poorer-performing paddocks, where it is sown instead of lupins.

Mingenew grower Paul Kelly, with agronomist Owen Mann, believes there are several significant benefits of including Margurita serradella in his continuous cropping rotation. Photo: Evan Collis

"In many years on these poorer areas, we were losing money by planting lupins, yet we still needed a break crop in the system," he says.

He says this will be his second year planting Margurita.

"While we don't yet have a definitive formula in regard to reducing the applied nitrogen in subsequent wheat crops, we know from the previous serradella plantings that we won't require the same amount of nitrogen on these subsequent wheat crops when compared to wheat on wheat.

"Ideally we would get to a point where some of the better-performing soil types may not need applied nitrogen at all."

Margurita in mixed enterprises

Another Mingenew grower who has been successful with serradella crops is Brett Broad, who is now in his third year of growing Margurita.

Brett, who farms with his wife Nicole and parents Ian and Diane, runs 1000 ewes and 120 cow breeders on his 6500ha.

Some of the research project trials, managed in collaboration the Mingenew Irwin Group, are on the Broads' property.

Brett introduced the serradella into the rotation for the same reason as Paul Kelly - to grow a break crop on poorer-performing paddocks where lupins were making a financial loss.

In 2018 he planted 500ha to Margurita and this year he has planted another 600ha.

Over the next eight to 10 years, Brett hopes to plant up to 3000ha to Margurita, which will become a break crop rotational tool, particularly in years when lupins won't be profitable.

The Broads have a range of soil types, and Brett says he will continue to plant lupins on his productive country, but in the marginal deep sands he says serradella is an excellent fit.

"We were having to throw everything at a lupin crop on these sandy paddocks just to make 1.5 tonnes per hectare in an average year, and then our paddocks were very exposed during the summer and autumn months," he says.

"But we still needed that break crop to give the paddocks a barrier against weeds and diseases, and to put nitrogen back into the soil."

Brett plants his Margurita in February, which he says allows him to test his seeding gear prior to his main seeding program in late autumn.

The Broads now have a rotation of serradella/wheat/serradella or other pastures.

"In the wheat rotation, we spray out any serradella plants when we do our broadleaf spray and hope that there are enough hard seeds left in the paddock for it to regenerate in that third year without having to be resown," Brett says.

"We are still learning about the benefits and the challenges of Margurita, but so far it's looking like it will be a permanent fixture in our rotation."

Brett is hoping there will be some benefits in terms of potassium availability for subsequent cereals. Brett says the biggest cost of planting serradella is the use of an inoculant. He says inoculant is critical for poorer-producing paddocks but it may not be necessary on loamy soils.

Further trials are underway to assess whether serradella responds to inoculation after the paddock has grown lupins, which uses the same inoculant.

National focus

The Rural R&D for Profit project has trials across Australia and includes research work from Murdoch University, the NSW Department of Primary Industries, CSIRO, the South Australian Research and Development Institute and Michael Moody Consulting.

While significant research on serradella occurred 20 years ago, the focus for the project now is to develop a variety that is short-season and easy to handle, to allow the crop to be a cost-effective, simple addition to any rotation.

"Developing new legumes is of no value unless farmers can afford to introduce them," Dr Yates says.

More information: Dr Brad Nutt, 0439 920 933; Dr Angelo Loi, 0429 378 279; Dr Ron Yates, 0427 550 125.