WATERLOGGING is not a problem commonly associated with the Mallee, but farmers in the region are increasingly watching their best land go underwater.
Mallee dune seeps - also known as freshwater seeps or soaks - usually begin as non-saline low-lying wet areas which gradually become waterlogged. As water evaporates and draws salt to the surface, areas become saline, unproductive and too wet to drive machinery over.
The number of seeps emerging across the Mallee has risen rapidly in the past decade, with land transformed from prime cropping country to useless, barren patches in just a few years.
A Natural Resources SA Murray-Darling Basin-led project - set-up in response to increasing concerns expressed by farmers - is investigating the cause of Mallee dune seeps and looking for solutions to minimise their impact and size. Soil scientist James Hall, Juliet Creek Consulting, and groundwater expert Chris Henschke are working with drill operator Simon Knowles and NRM SAMDB team leader - land management Bernadette Lawson to examine water movement and seep development at four sites across the Mallee.
The increasing problem is being attributed largely to long-term use of no-till continuous cropping systems.
While no-till cropping has revolutionised broadacre farming in the Mallee, the practice of spraying summer weeds to conserve soil moisture may be contributing to the increase in seeps in the region.
Click on the image above for more images of the drilling process
"Often it's the best land that these farmers are losing - it's getting so wet that it's no longer cropable, and machines are getting bogged because it's so waterlogged," Mr Hall said.
"These systems tend to be located adjacent to dunes. The theory is that these dunes are not producing well - given that yields of dunes haven't really improved in the past 40 years - and the crops are not using the available moisture.
"With all the summer spraying that's happening, that focus on keeping weeds under control means they're not using any summer rain, and the water has got to go somewhere."
At Kulde and Mannum, the first signs of change emerged in 2005 and by 2010-11 the affected areas were unable to be cropped, Ms Lawson said.
Water appears to be moving below the surface from sandhills or dunes to low-lying areas, with the project aiming to identify the depth and magnitude of this movement.
"We're looking at two theories with this project - is the water moving in the top soil, moving downhill at a depth of about 50 centimetres, or are there deeper systems involved?" Mr Hall said.
The initial stages of the project involve drilling a series of narrow exploratory wells at each site to examine soil layers and allow for the installation of piezometres, which will measure groundwater pressure deep in the soil.
This will allow the group to monitor water flow throughout the year.
Drilling on sandy slopes at Mannum and Kulde has revealed a saturated layer about 6 to 6.5 metres below the surface, suspected to be sitting just above a layer of impermeable Blanchetown clay.
"The drilling has helped us find out a lot, but it's still always surprising to find a saturated layer in the soil," Mr Hall said. "Here we are in the driest state, the driest continent and we've got all this water.
"What we've found so far is that most of the water seems to be down in the deeper systems. It's not confirmed yet but it looks like Blanchetown clay appears to be the culprit.
"The water comes up where there's a layer of that Blanchetown clay close to the surface, and that's where we're seeing these seeps and waterlogged areas."
The project will trial a number of possible management options, including the use of high water use plants such as lucerne, perennial salt tolerant shrubs and strategic tree planting.
