- 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 (PBR), 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.
GRDC has produced a video outlining the potential of summer sowing hard-seeded serradella in the western region.
Assessing the benefits
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 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);
- chemical fallow; and
- weed control.
Summer planting strategy
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.
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.
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.
Value in a continuous cropping enterprise
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.
Dr Yates says introducing the hard-seeded serradella into a mixed crop and livestock operation makes perfect sense.
"But what if you don't have livestock? That's the question growers have been asking," he says.
"Should growers with a continuous cropping business consider serradella in their rotations and, if so, why?"
Dr Yates says some growers, particularly in lower-rainfall regions, have paddocks that may be difficult to crop, or be marginal in terms of crop profitability.
"This is where serradella can really work for you; it seems to thrive in those poorer soils, and allows the soil to be regenerated to be suitable for cropping in subsequent years," he says.
"Previously, the only options you had were the traditional annual medics or subclover."
It seems to thrive in those poorer soils, and allows the soil to be regenerated to be suitable for cropping in subsequent years.
The root systems of the new plants have greater biomass and penetrate deeper than the traditional legumes, allowing the plants to grow later in the season - particularly on the less-fertile soils.
Dr Yates says the other significant benefit for a cropping enterprise from a serradella crop is the 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 serradella can reduce nematodes in the soil."
Preliminary research is showing that one year of serradella is sufficient to dramatically reduce nematode population numbers and allow subsequent crops to have reduced impacts.
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 (PBR) 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.
"For growers to consider serradella in their rotations, it must be cost-effective and easy to handle, and our breeding efforts to date have ensured this is now the case."
Grower experience of Margurita in a continuous cropping rotation
Mingenew grower Paul Kelly has a continuous cropping enterprise that now includes the summer-sown Margurita (PBR).
A registered pasture producer for many years, 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.
"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.
"While serradella may not be a cash crop for us, it ensures we don't lose money, because once it has been planted it will stay in the system for many years."
Paul says this will be his second year of planting Margurita (PBR).
While serradella may not be a cash crop for us, it ensures we don't lose money, because once it has been planted it will stay in the system for many years.
"We have planted soft-seeded serradella previously and so we know there are significant carry-over nitrogen benefits for cereal crops from this pasture legume," Paul says.
"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."
In 2018 Paul planted 110 hectares to Margurita (PBR) and this season he has put in another 70ha.
"We will continue to plant it, and take care of it, so it can regenerate in future years," Paul says.
Grower experience of Margurita in a mixed enterprise
Another Mingenew grower who has been successful with serradella crops is Brett Broad, who is now in his third year of growing Margurita (PBR).
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 (PBR) and this year he has planted another 600ha.
Over the next eight to 10 years, Brett hopes to plant up to 3000ha to Margurita (PBR), 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."
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.
Brett plants his Margurita (PBR) 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 (PBR), but so far it's looking like it will be a permanent fixture in our rotation."
Brett is also hoping there will be some benefits in terms of potassium availability for subsequent cereal crops.
"We will be really interested in the soil testing results in the trials so we can put some numbers on what the Margurita (PBR) is doing in terms of nutrient availability," he says.
Apart from buying seed, Brett says the biggest cost of planting serradella is the use of an inoculant.
He says inoculant is critical for poorer-producing paddocks, but on loamy soils it may not be necessary.
Further trials are underway to assess whether serradella responds to inoculation after the paddock has grown lupins, which uses the same inoculant.
National focus of pasture collaboration
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