Researchers at the University of Queensland are investigating how fire and grazing can be managed to maximise the natural carbon and nitrogen inputs by biocrusts into soils, with the aim of improving the productivity of grazing lands in northern Australia. Soil fertility is a major limitation to pasture growth in tropical savannas like northern Australia, but adding fertilisers at extensive scales is highly inefficient and expensive.
Researchers believe they have an answer: the enhanced plant growth and soil moisture, fertility and productivity found in soils below biocrusts. Currently, their hypothesis is being tested with biocrusts are being put through their paces at the Kidman Springs fire experiment 400 km south of Darwin (Northern Territory Department of Industry, Tourism and Trade) and the Wambiana grazing trial in north Queensland (Queensland Department of Agriculture and Fisheries).
Found across the world, from freezing Antarctica to hot savannahs, biocrusts are a web of tiny, living organisms, including cyanobacteria, fungi, green algae, bacteria, lichens, liverworts and mosses. Stabilising the soil surface, photosynthesising thus enhancing soil carbon, and fixing nitrogen, biocrusts are the ‘living skin’ of the soil. Growing on the top 1-2cm of soil, these living soil crusts cover the bare spaces between plants and change appearance, between brown and green, dependant on the seasons.
Biocrusts in Australia’s tropical savannas, like our native vegetation, have evolved with fire and hence are well adapted to fire. Removing litter, trees and shrubs that would otherwise compete for ground cover, the right amount of fire can enhance biocrusts. By the same token, grazing can also potentially clear vegetation over and open up spaces for biocrusts to flourish. However, unlike its fire adaptations, our native vegetation struggles with the trampling of hooved species. The researchers at the University of Queensland, understanding this, are trailing methods of management in both project sites.
Noting promising results, fire trials in the Kindman Springs site saw the regrowth of biocrusts after fire, of the same quality as those in unburnt sites. At the Wambiana grazing trial near Charters Towers, biocrust cover was higher and healthier with moderate grazing than with heavy grazing. Future work will examine what this means for nitrogen inputs.
If you would like more information regarding the role of biocrusts in the Northern Territory rangelands, contact Dr Robyn Cowley, Senior Rangeland Scientist, on 0419 829 493.
Additional information about the Boosting natural regeneration of the nitrogen capital in grazing lands (Biocrusts project), contact Wendy Williams, the University of Queensland Project Manager, on 0418 246 001.
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