Secret soil cracks linger underground

Posted 17 May 2012

Deep cracks in soil that appear during long dry spells can remain open underground even after they have visibly sealed on the surface, a new study has found.

The results could have important implications for agricultural management around the timing and intensity of water and pesticide applications.

"These soils are very fertile and provide the most productive agricultural land in Australia," said lead author Dr Anna-Katrin Greve, a postdoctoral fellow with the Connected Waters Initiative.

"Lower water application intensity will give soil cracks time to close and more frequent irrigations could prevent the soil cracks from reforming."

These cracks, which form during extended dry periods, provide "preferential pathways" allowing water to flow much faster than it would through non-cracked soil.

This means nutrients and pesticides are rapidly transported beyond the crops' root-zone, said Greve, and if the plants can't access the water it has effectively been wasted.

By sending an electrical current through the ground at different angles, the UNSW researchers can measure directional differences in current conduction, which offers clues about how water is moving through the soil.

This innovative technique means they can, for the first time, detect the exact time when preferential sub-surface pathways close. This is important for irrigators, as water flow through non-cracked soil is far more predictable.

Their findings, which have been accepted for publication in the journal Geoderma, reveal that surface appearances can be deceiving.

"We showed that soil cracks that developed in dry periods remain open as preferential flow paths, even after the cracks are visually closed," said Greve.

Researchers measured the flow of electrical current through a soil profile that was set-up over several years. The soil was contained in a fiberglass barrel, which had a small drain at the base.

Two irrigation events were carried out approximately 14 days apart. Each event used water from different sources, meaning the two samples had different stable isotope signatures, allowing researchers to distinguish between them.

At the time of the first irrigation event there were visible cracks upwards of three centimetres wide in the soil. By the time of the second irrigation, these cracks had visibly closed.

Despite this surface closure, the water from the second irrigation actually drained faster. It bypassed the sections of the soil where water from the first event was presumably stored and drained with signs of limited mixing, researchers said, meaning preferential flow paths must have remained open.

Greve's study was awarded best paper at a geoscience conference in Europe in 2011 and she recently presented her findings at a conference in Arizona.

Links

Latest news

Ancient water to drain from farmland without ongoing joint management

Ancient water to drain from farmland without ongoing joint management

1 July 2020

The management of withdrawals of ground water in the Central West remains an area of hotly-contested debate. Associate Professor of Hydrogeology Bryce Kelly has spent over a decade studying groundwater in the Central West, and has credited groundwater with “saving rural communities from collapse”, but its potential for future drought-proofing depends on how successfully it’s managed. He says current withdrawals “will only be sustainable if the Narromine region gets flooded frequently enough to balance the volume of groundwater extracted."

Read more…

GWI Global Water Matters Podcast

21 June 2020

The UNSW-GWI Global Water Matters Podcast was launched in 2020 to share interesting and important water-related developments and insights from global experts across the broad spectrum of water-related disciplines. Born from the demand to continue the Water Issues Commentary seminar series under the constraints of social distancing, new episodes are released monthly.

Read more…

The mystery of Thirlmere Lakes

The mystery of Thirlmere Lakes

22 May 2020

During the past decade, water levels in the Thirlmere Lakes have varied from full in 2016 to completely dry between October 2018 and February 2020. These variations have raised concerns with the local community and left them wondering; "Where has all the water gone in Thirlmere Lakes?"

Thirlmere Lakes National Park, located south-west of Sydney in an ancient river meander, contains five lakes – Lake Gandangarra, Lake Werri Berri, Lake Couridjah, Lake Baraba, and Lake Nerrigorang. 

Two WRL research teams (EcoEng and Connected Waters) have investigated the water balance budget and surface-groundwater interaction in Thirlmere Lakes. These investigations were supported by coordinated research projects with ANSTOUniversity of Wollongong, and the NSW Department of Planning, Industry and the Environment (DPIE). In collaboration with these groups, WRL engineers undertook extensive fieldwork between 2017 and 2020 to monitor the site, including remote sensing bathymetry surveys, deploying micro-meteorological stations for measuring evapotranspiration, and installing a piezometer network for groundwater investigations.

Read more about the research findings here.  


Read more…

Subsidies drive Murray-Darling Basin extractions as environment loses

Subsidies drive Murray-Darling Basin extractions as environment loses

21 May 2020

Subsidised irrigators extracted up to 28 per cent more water than those who received no funds under a national Murray-Darling Basin irrigation efficiency program, a new study has found.

Read more…

Groundwater resources in Africa resilient to climate change

Groundwater resources in Africa resilient to climate change

8 August 2019

Groundwater – a vital source of water for drinking and irrigation across sub-Saharan Africa – is resilient to climate variability and change, according to a new study.

Read more…