Looking below the surface: Lessons from the landscape

Posted 20 December 2016

Macquarie University researchers have been sampling ground water on farm.

Republished from Spotlight, Summer 2016-2017

In the last edition of Spotlight Dr Oliver Knox spoke to several researchers who have an interest in the biology of our cotton producing soils. They talked about the soil biology’s abundance, diversity and some management decisions that could help to improve it, but in doing so we really only scratched the surface of what we know…

In this edition Oliver has brought together information from some of the industry’s researchers conducting work on our farms’ soils and associated environments in areas where we aren’t farming. The soil biology of the native vegetation on cotton farms indicates what was probably there before, what we’ve lost through cultivation and what functional changes this might have on our soils.

One of the best loved examples of our native vegetation areas are the river red gums and Dr Rhiannon Smith of UNE has been looking at these in the cotton landscape for over a decade.

Of these trees Rhiannon says, “River red gums capture the hearts and minds of Australians and as such, these gums are an important focal point for monitoring riparian health and condition.”

Dr Rhiannon Smith says river red gums sequester and store large amounts of carbon.Dr Rhiannon Smith says river red gums sequester and store large amounts of carbon.

Of course this is not all they do.

“Healthy river red gum ecosystems on cotton farms provide important ecosystem services and sequester and store large amounts of carbon, which feeds the soil biota that stabilises soils and riverbanks, stopping slaking and dispersion of soil aggregates, and reducing sediment flows into river systems,” Rhiannon says.

“Riparian river red gum forests can store up to 400 tonnes of carbon per hectare, with approximately 40 percent of this carbon stored in the soil, and can sequester an average of 5.3 tonnes of carbon per hectare per year in woody biomass.

“Riparian vegetation dominated by river red gums plays an important role in offsetting carbon emissions on cotton farms.”

So the trees are clearly important, but we can go further!

It’s a living thing

Dr Kathryn Korbel from Macquarie University is focused on the microbes and animals within groundwater. Kathryn’s work has shown that the abundance of trees as well as agricultural practices can have an impact on the groundwater biota (stygofauna and microbes) and potentially water quality. But what are stygofauna?

“Stygofauna are predominantly small crustaceans similar to invertebrates that we find in our rivers, but due to the lack of light in the groundwater environment, these animals are transparent and sightless,” Kathryn says.

Main image: An amphipod, another of the invertebrates we find living in the ground water depending on its quality. Inset: Syncarids, about the length of a 20 cent piece, are a type of stygofauna, blind invertebrates that dwell in out groundwater and can help predict its quality.Main image: An amphipod, another of the invertebrates we find living in the ground water depending on its quality. Inset: Syncarids, about the length of a 20 cent piece, are a type of stygofauna, blind invertebrates that dwell in out groundwater and can help predict its quality.

“In fact, some of them are known to move between ground and surface water when conditions are favourable.

“By looking at these animals we can gauge groundwater quality.

“Our work has also focused on the bacteria within the groundwater, which are believed to be important in influencing water quality, ensuring groundwater remains suitable for drinking and agricultural uses such as irrigation.

“It has become apparent that bacteria are important in the nitrogen, carbon and iron cycles within groundwater, with microbes possessing the ability to degrade nitrates being located in our focus catchments.

Charlotte Iverach, UNSW, sampling greenhouse gases at the soil air interface.Charlotte Iverach, UNSW, sampling greenhouse gases at the soil air interface.

“Although more work on this is needed, results potentially indicate microbes may have a role in remediation of contaminated groundwater.”

For cotton farms and farmers, this research is highlighting the links between biology in the groundwater and water quality, which in turn has implications for the wider environment that includes our cotton production systems.

Monitoring quality

The groundwater microbiology and the soil microbiology are also the focus of one of Dr Bryce Kelly’s projects in which they started analysing the soil and groundwater microbiology to enable better interpretation of the air and groundwater methane surveys being conducted in the Condamine Catchment.

When Dr Sabrina Beckmann at UNSW started analysing the vertosols from the Condamine Catchment, she noticed that the soil microbial communities found under native vegetation, traditionally fertilised irrigated cotton crops, and bio-fertilised soils were different.

“Farming practices appear to have reduced the abundance of bacteria and archaea in soils when compared to adjacent native vegetation areas,” Bryce tells us.

This insight is important, because little is known about how historical farming practices originally altered the soil microbial populations in Vertosols. Modern farming methods appear to be rebuilding soil health from a low base.

The microbiological community controls soil health, plant disease resistance, nutrient uptake, and the production and consumption of greenhouse gases. We can learn from healthy native vegetation soils to guide the way we rebuild the bacteria and archaea in farming soils.

Measuring the chemistry of the ground-level atmosphere tells us a lot about microbiological processes occurring in soils. At the district scale Bryce Kelly and Charlotte Iverach have noticed that cotton farming districts have slightly lower ground-level atmospheric methane concentrations compared to areas of native vegetation. They are now trying to quantify to what extent farming landscapes are a sink for methane.

Bryce is also developing methods for the continuous measurement of nitrous oxide emissions at the district scale. He is measuring continuously both the concentration and isotopic compositions of the gases, which provides insights into sources of the gas. His long term aim is to develop automated greenhouse gas accounting methodologies.

How do we tie the research together?

“We’ve recognised the role of soil biota in providing ecosystem functions for sustainable productivity and maintaining our soil and water resources in our intensive cotton cropping systems in Australia for some time,” says CSIRO’s Dr Vadakattu Gupta.

“As others have said, soil microorganisms, along with fauna mediate carbon and nutrient cycles and play a critical role in disease suppression, degradation of agrochemicals and the maintenance of overall plant health and soil structure.

Taking soil cores as part of Dr Rhiannon Smith’s work on river red gums and their immense value to the landscape.Taking soil cores as part of Dr Rhiannon Smith’s work on river red gums and their immense value to the landscape.

“Crop management practices such as crop rotation, tillage, crop residue retention, fertiliser and agrochemical application have been shown to influence the abundance and composition of soil biota communities with potential impact on biological functions, but currently, there is very little information available comparing the composition of soil microbiology in cotton soils with that in remnant native soils.”

What’s the difference?

Rhiannon Smith says river red gums sequester and store large amounts of carbon

Gupta has set about remedying this knowledge gap as part of a larger program called the Biomes of Australian Soil Environments (BASE).

“What we found was a clear difference between cotton fields and remnant vegetation,” he says.

“Bacterial diversity in soils has been shown to be influenced both by the soil and environmental factors, so the observed differences in the soil microbiology between cotton fields and remnant vegetation could be partly due to the variation in soil chemical properties, which were seen with organic carbon, phosphorus and mineral N all being higher in the native samples.”

 There is of course still more to learn about our soil biology and Gupta reminds us to be cautious, as to date the sequencing analysis conducted has been limited and multi-site and well replicated analyses is warranted in order to confirm these preliminary observations.”

One soil, many facets

So by examining the soil biology in our fields, some of the functions and biology associated with our native vegetation and ground water and what we know about the differences between these.

“We see that there are established linkages between our productive fields, our native veg areas, river systems and our farms within the wider environmental setting,” Oliver says.

“We’re still learning about the biology in our soils and environment, but generally the more diverse it is the more resistant it is to change and the more resilient it is, in that the soil biology recovers more quickly when a change occurs, so we can keep farming.”

Coming up…

Over the last editions of Spotlight we’ve taken a brief look at the soil biology of our fields and the influence and importance of our native vegetation, so the final chapter is capturing the views of growers who have recognised the importance of soil biology and in doing so have adopted some of the strategies we’ve discussed to improve soil biology. Stay tuned for the next edition of Spotlight to meet these growers and hear about their methods.

In the meantime, if growers or consultants have any questions about the work being undertaken by these researchers, please feel free to get in touch with them or Oliver via the links below:

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