- Trial Rationale
- Steps Taken
- Lessons Learnt
- Looking Forward
Generally, current farm practice to reclaim weed burdened, low fertility land is to allocate (20-40%) to unproductive fallow for 1 or 2 years to allow tired soil to recuperate.
Unproductive fallow is low cost option, however fallow vegetation has the following limitations:
- provides only low quality feed for stock;
- clover-based pastures tend to lack biomass and grow inconsistently on soil with varying structure and carbon levels; and
- weeds also propagate disease and consume nitrogen, other nutrients and moisture during the growing season, leaving less for the following grain crop.
Lake Grace Farmers, Craig and Anna-Lisa Newman, had recently purchased additional land and were planning to invest up front to improve the health of the soil. “We had acquired the farm and were looking for some support to invest heavily upfront in its longer term sustainability,” Anna-Lisa said. With a cropping ratio of 65-70% to 30-35% sheep, cropping is the Newmans’ main business enterprise with their 7000 ha owned
land and 1800 ha leased. Craig said they first learnt about serradella legumes at a GRDC Crop Update in 2014.
The aim of the trial was to establish hard-seeded serradella variety Margurita to replace weeds and improve general soil health of low value land. The Newmans also wanted to explore the opportunity to lower fertiliser input costs and reduce the risk of acidification on sandy soil.
The paddock history of the recently acquired trial area includes continuous cropping, high weed burden, low pH and low soil nutrition. The three-year recuperation plan developed in consultation with Dr Angelo Loi from the Department of Primary Industries and Regional Development (DPIRD) consisted of:
- 2016 – summer grown Margurita with the aim of achieving maximum establishment and seed set (some of which would be harvested for use elsewhere on the farm);
- 2017 – IMI (herbicide) resistant canola (due to the need to use substantial amounts of herbicide in the Margurita establishment phase); and
- 2018 – allow Margurita to regerminate, control weeds and achieve a high seed set to establish the seed bank to last the next two years of cropping.
The trial area was sprayed twice over summer 2015 to control wild radish following high rain events of 60 mm and 95 mm respectively, then again in February prior to seeding in March 2016 at the rate of 14 kg/ha Margurita at a depth of 2 cm into moist soil. Fertiliser applied at seeding included Whitfert 3:1 Plain Super with K at a sowing rate of 75 kg/ha including P and K. Additional nitrogen fertiliser was not applied.
According to Dr Loi, the most critical step to ensure successful Margurita establishment was to apply one more post sowing/pre-emergent dose of Spinnaker herbicide to prevent competition from weeds during germination. 100 mm rain was received in late March, which triggered rapid germination, though it appeared early on that some patches of capeweed survived the earlier herbicide applications. Only 12 mm of rain was received in April but the soil remained moist and saw strong growth by the Margurita (Figure 1), which was very helpful to maintain stock weights during the autumn feed gap. Angelo recommended maintaining steady grazing pressure on the Margurita during periods of high rainfall because it tends to grow too fast otherwise.
Selective spraying on patches of Rye Grass was carried out in May to prevent competition with the young Margurita plants. Pasture cages to compare biomass of grazed and ungrazed pasture were installed in June. Light grazing pressure was maintained into winter and a second effort at selective weed control was carried out at the end of July to remove late germinating weeds and keep the pasture as clean as possible. Average rainfall was received over June and July. Dry biomass was sampled and measured in early August. Sheep were removed in late August to allow the Margurita to bulk up, flower and set seed. To remove the sheep any earlier would have been to risk making harvesting harder due to excessive biomass. Finally, insecticide was applied in mid-September due to the high risk of budworm infestation.
Dry biomass of the continually grazed Margurita (low 3.2 DSE) was measured at 2.2 t/ha, compared to ungrazed pasture in the cage measured at 3.2 t/ha. Margurita seeds were harvested in October 2016 and the Newmans recovered enough seed to establish a further 1700 ha the following year. One of the practical lessons Craig learnt for working with Margurita is to harvest sooner rather than later. “Don’t leave harvesting too late as everything becomes brittle, breaks and won’t go through the header properly.”
40 m strips of Margurita were subjected to wet and brown manuring and compared to chemical fallow in the following Canola crop, sown in May 2017. Canola yield results concluded that the chemical fallow strips underperformed by 800 kg (1.2 t/ha) compared to the Margurita plot (2.0 t/ha) when not treated with nitrogen. Soil tests and in season tissue tests all demonstrated that the nitrogen levels in the Margurita treatment strips were consistently much higher than in the chemical fallow strips. This transpired into yield gains and economic return. The better establishment rates of canola grown on Margurita treated soil can be seen clearly over chemical fallow in Figure 2 below.
After comparing canola yields (Figure 3) following Margurita and chemical fallow without nitrogen fertiliser, the Newmans realised their previous strategy of spreading high quantities of urea are no longer necessary if they continue to use legume pastures between cash crops. “We have determined that there is enough nitrogen available from the plant to grow a profitable crop, without the need for any additional nitrogen,” Craig said.
“Once the establishment phase is over, the Margurita works best in a two crop, one Margurita rotation as the seed bank is huge. The nitrogen produced is definitely enough for the first crop and much of the second crop depending on the Margurita biomass achieved.”
Overall, the available nitrogen stored by 5-6 t/ha Margurita in the 2016 season, will return almost all of the initial establishment costs of $100-$150/ha within one year. This was achieved by reducing the need to continue to control weeds and the value of the seed harvested (as opposed to purchasing more to expand Margurita pasture over a wider area the following year. Additionally, the value of the land purchased has increased significantly since purchase in 2015, a large part of that was attributed to the legume rotation, reduced weed burden and successful cropping phase following it.
The biggest challenge the Newmans found was sticking to the Action Plan and not getting distracted by activities elsewhere on the farm. The assistance of Dr Loi was paramount to obtaining results for the trials, which boosted the Newmans’ confidence that what they were seeing really was improving the soil’s productivity and improving their financial bottom line. “We were able to report anecdotal evidence and yield data from the header, which supported the trial findings,” said Craig. They also learnt about nutrient management such as how deep rooted legumes raise subsoil potassium into the topsoil. This is an added benefit to the project.
“If it wasn’t for this trial, we would have attempted to run stock on volunteer pasture. Overall nutrition for the following crop would have been poor and the stock carrying capacity reduced by the need to control volunteer weeds in season. Instead we were able to stock early and at high rates throughout winter and the following summer thanks to the high biomass residues.”
Following the extremely positive results of the trial, the Newmans have taken up establishing legume pastures across all of their farms and are constantly looking for new ways to generate further returns on investment. The Newmans have taken their learnings on board and have sown 1900 ha of legume pasture in 2017 and 2600 in 2018. This leaves a remaining 500 ha to implement in 2019 to complete 6700 ha of regenerative legume pasture. Some areas more alkaline will use Biserrula instead. “The implementation of serradella and Biserrula legumes across all our farms will no doubt be a pivotal moment for our farm’s history. We are excited about its future,” Anna-Lisa said.
“Other farmers have seen what we have achieved and noted the incredible growth of the canola following the Margurita in 2017. Even though we planted late season with the farm having the smallest rainfall figures, it out yielded our earlier crops.”
The Newmans now want to learn how to measure legume biomass in season and use this to calculate nitrogen application rates to maximise nutrient use efficiency. “Looking at our livestock enterprise, we anticipate more wool and higher stocking rates so will be monitoring these commodities. We also want to reduce our reliance on artificial nitrogen and only use minimal amounts,” Anna-Lisa said.
“We believe we are working toward a more balanced and holistic approach to our farming system that is still grounded with very sound economics.”