Many cattlemen and women would have seen it in their grazing paddocks countless time before, but never given it a moment’s thought.
Cyanobacteria are those black, dark-green or reddish brown crusts that commonly form on areas of soil or rocks after the wet season.
Research is unearthing greater knowledge about the little known world of cyanobacteria, which could hold a key to boosting both soil nitrogen and carbon levels in grazing land across Australia.
Researchers are learning more about the beneficial nitrogen and carbon-fixing roles these bacteria play, which could ultimately lead to greater productivity from native and improved pastures in grazing areas – particularly if their activity can be enhanced or introduced to new areas.
Producers attending CCA and AgForce’s recent Northern Beef Steakholder forum in Mt Isa gained some insight into recent research into cyanobacterial soil crusts from the University of Queensland’s Dr Wendy Williams.
Cyanobacteria are microscopic organisms that live on the surface of the ground. They are found naturally across large parts of Australia, particularly away from coastal areas.
While often only 20 microns in size, they cluster in communities in their millions, making them often easy to see in rangeland situations. The bio-film on the soil surface can vary from less than 1mm in thickness, to easy-to-spot deposits up to 10mm thick.
“The reason why we are interested in them is that firstly, they photo-synthesise the same as plants, and secondly they fix nitrogen, the same as legumes,” Dr Williams said.
“The only difference between cyanobacteria and legumes is that cyanobacteria do not need a rhizobial partnership to fix nitrogen like legumes do – they have their special cells to do it.”
The nitrogen in a cyanobacteria colony is stored in a slimy outer coating, which is washed-off after rainfall into the soil, to the benefit of surrounding pasture. And because the nitrogen is in the form of ammonium, it is immediately available to plants.
Dr Williams said at this stage, the core interest in learning more about cyanobacteria was to understand how and why they function, and whether that can be harnessed in some way to boost pasture performance.
While much of her Mt Isa presentation was based on research in summer-dominant central and northern regions of Australia, cyanobacteria could be found virtually everywhere in Australia, only their life cycles tended to differ depending on the climate.
“One of the reasons we are focussing on them is that they are plentiful – most people working in the cattle industry will have seen them, in one form or another. They can be commonly found in grassland areas as black crusts in places during drier times of year. In summer, when rains arrive, they grow and take on a greener sludgey/slimey form.”
The organisms need very little moisture at the right time of year to activate, and unlike annual plants, when they dry out, they simply reactivate, rather than dying off and having to re-establish from seed.
Within the crust or slime, there were a lot of different organisms present that added to the whole bio-crust structure, and the organic matter it creates.
“What we’re really interested in is understanding the system and the organisms, so we can use that to help in increasing organic matter in the soil, as well as increasing nitrogen production,” Dr Williams said.
“We’re getting a better understanding of how important they are in what they do, and what they put into the soil.”
Research is focussing on determining the peak growth time; what can be done to enhance their presence and distribution in the paddock; and how this may help future productivity.
Trials starting in 2009 took equipment into the field for two years looking at seasonal patterns, and not surprisingly, the peak activity was found to be during the northern wet season.
“But what was a little surprising was that the peak activity actually occurred in the February-March late-wet season period, not earlier. Nor could the crust be re-activated with (artificial watered) rainfall during the dry season,” she said.
This varied from bio-crusts seen in southern Australia and other parts of the world, which activate within minutes at any time of year, given moisture.
Equipment measured carbon sequestration and breakdown of the crust material, rich in carbon and nitrogen at the beginning of the wet season each year – at the ideal time for new season pasture growth.
“It’s part of the reason why grass protein levels after the first few rains into the wet season are pretty crash-hot, and then tend to even-out across the wet season,” Dr Williams said. “Later in the wet season, there is still nitrogen being fixed, but you don’t get that big influx of organic matter.”
Measuring equipment at test sites overseas had confirmed that cyanobacteria have a very positive influence in terms of both carbon sequestration and nitrogen fixation. This was also reflected in protein levels and dry matter yields in grasses.
“Nitrogen fixing performance varied enormously, but has ranged from 1kg/ha of additional nitrogen to 100kg/ha in overseas trials,” she said.
Similar field trials in Australia will start next wet-season, to determine nitrogen fixing and carbon-sequestration potential under a range of local conditions.
Globally, cyanobacteria bio-crusts have been shown to contribute at least 7pc of soil carbon and 45pc of biologically-fixed nitrogen, and results so far from the northern research project supported these findings.
“The good thing is, they’re free and available in your paddock now,” Dr Williams told the Mt Isa audience.
“The challenge now is learning how to manage them in order to get the best out of them, and to improve their performance. Our future research will focus on ways to extend their value, such as managing the resource to keep them growing longer during the peak periods to optimise nitrogen output.”
Asked whether the organism could be propagated and ‘sown’, she said they were easy to grow over the summer rainfall period in any damp shallow area that would retain water for a period.
“We’ve been starting to consider how to actually spread the organism. It may be they can be grown each year fairly easily and applied, perhaps from the air, to areas that do not have a high presence, or have been affected over periods of time for whatever reason. While the organism is found in agricultural systems, regular cultivation, for example, will reduce their presence.”
- Dr Williams’ research project has been supported by AgForce North, Qld Parks & Wildlife, MMG Century Mine, Primary Industries Longreach, the Australian Geographical Society, the Universities of Qld and NSW, and Kaiserlautern University (Germany).