Environment and profit drive mallee research
GroundCover™ Issue: 35
Change is in the wind for 4 million hectares of low-rainfall, mallee country in Victoria, New South Wales and South Australia.
And it's not just a figure of speech. A major issue is wind-borne erosion of the light soils that dominate the area. Concern over erosion both at the community and government level has catalysed a search for different farming systems under the umbrella of the Mallee Sustainable Farming Project.
"The Mallee remains one of Australia's hotspots for dust storms," says Farming Project CEO Marion Murphy, citing research documenting this fact.
The need for change has become even clearer with increased cropping in previously grazing-dominated areas and with continuous cropping an emerging key solution.
Optimistic projections say improved farming systems could offer the mallee country a production boost worth $200 million annually.
Salinity moves to top of list
Erosion has been joined by the growing spectre of groundwater recharge in this broad stretch of the Murray-Darling Basin. Both environmental aspects underpin the third key farming issue: increasing productivity.
Growers and the Federal Government through the GRDC have committed more than $1 million in research support since 1997 to lift the area's production statistics. To put that in perspective, one researcher documented a 15 per cent production increase in the SA Mallee over 30 years, while the higher rainfall parts of that State logged a 52 per cent increase. (Additional major support for the organisation comes from the Federal Government's Natural Heritage Trust.)
Mallee soils are often highly alkaline, low in organic matter and have free limestone present. This is presenting challenges in defining optimum nutrition and herbicide management. A typical light mallee soil is a sandy loam with about 8 per cent clay content (see 'Sustainable systems don't blow', left).
To fallow or not to fallow
A big question for the partnership of 160 farmers and researchers centres on the long-term role (if one remains) for traditional long fallow, compared with a continuous cropping model, which minimises bare ground and may help ameliorate salinity.
The on-ground organisation is designed to maximise farmer involvement across the millions of hectares of the project area, spanning 1,500 farm businesses from the Adelaide foothills to Kyalite in NSW.
"Mallee farmers have been forced by the marginal environment to be conservative, and need to see a system working locally before they will adopt it," says Ms Murphy. Adds NSW district agronomist Graeme Mcintosh: "Risk aversion is a natural response for farmers when one in three seasons is likely to be pretty ordinary".
In response, the project has set up on-farm focus paddocks (currently 46) providing a reality check for research results from three regional trial sites. Last year, farmers Tony Robbins and Ian Hastings received a Victorian Government award for introducing the unique concept of focus paddocks.
Back paddock research
Researchers and farmers are testing crop rotations, nutrition and inputs generally, tillage systems, and the economics related to continuous cropping models — within a mixed farming operation in most instances.
Strategies are also being refined to minimise the erosion impact of fallowing which is still favoured by the 65 per cent majority of farmers in the Mallee. It has been the traditional low-cost risk management system.
For tillage practices to change, a high priority for research is to look at the action of herbicides in mallee soils. "We are wary of solving one environmental problem (erosion) by creating another — herbicide contamination," says Ms Murphy.
The sensitivity of legumes to herbicides used in the cereal phase is a problem. In initial trials, nodulation and related nitrogen fixation were depressed following the application of the most widely used herbicides.
In addition, researchers have reported that, based on soil texture, soil alkalinity and rainfall, soils at all the focus paddocks and at the core sites were in the Very high risk' category for sulfonylurea (SU) carryover for two or more seasons after application.
Legumes, canola, barley and oats are all susceptible to SU contamination.
A promising line of research by Vadakattu Gupta from CSIRO Land and Water suggests that microbial activity could be modified to reduce the persistence of SU herbicides in alkaline soils.
The project seeks profitable solutions but it also quantifies the risks of groundwater recharge and soil erosion. Novel farming systems are under the microscope: for instance, the use of precision techniques to combine crop and fallow in the same paddock.
Results and possible strategies are reported annually to the broader farming community.
Network of advisers
A network of private agronomists is providing best management support for the 46 focus paddocks. In the process some long-held beliefs are being given a hard look. For instance, in the Mallee's low-rainfall environment, research is showing root disease (related to more intensive cropping) doesn't limit productivity as much as inadequate nutrition does.
"Our results challenge the necessity for fallowing in the sandier mallee soils, particularly since we are finding that the loss of moisture and nitrogen that occurs counteracts the benefit of fallow. The jury is still out on the heavier mallee soils," says David Roget, CSIRO Land and Water.
"We are well on the way to developing a farming system of crops in most years, subject to rainfall, with a periodic phase of deep-rooted perennials to access moisture and nutrients down to 6 metres. Results to date are showing increased profit and sustainability with this system."
The project uses benchmarks of yield, WUE, soil erosion, and gross margin.