The importance of quality subsoils
When working with wheat and canola farmers in southern Australia, La Trobe's Dr Peter Sale made a discovery. He found that poorly structured subsoils, 10 to 30 centimetres below the topsoil, created significant barriers to the growth of crop plants.
‘Australia is a very old continent so the soils are very old,' he says. 'Sub-soil problems can mean roots are restricted in deep-root growth.’
His colleague, Professor Caixian Tang, says it’s common for subsoils to form a dense clay that roots can't penetrate.
‘If the plants have a very shallow root system, they can’t access the water from the deep soil layers, so it causes an early end to their growth at the end of the crop cycle. They can produce beautiful shoots but can’t finish their crops.’
Obviously, drought has had a major impact on Australian farming, but even with high rainfall, farmers struggle with problematic subsoils.
‘You can have too much water,' Professor Tang says, 'because the soils are so dense the water won’t drain. Nothing grows in the water-logged soil and then, when the water logging disappears, the plants have short roots.’
For a farmer whose livelihood depends on food production, the outcome for the crop can be very disappointing.
As Australia is among the world's major food producers, crop failure can also put a hole in not only the local economy and the export of grain to world markets.
Transforming the physical properties of soil
Once upon a time, the research community believed large-scale subsoil improvement would be impossible. How on Earth could we access deep subsoil, below the surface, over large areas, in a cost effective way? Against the odds, the La Trobe team found a way.
What started as a small trial has developed into a promising technology: subsoil manuring.
Subsoil manuring converts hard, dense clay into soft, pliable soil – like in your veggie patch.
‘In a nutshell, we’re putting down narrow bands of nutrient-rich organic amendments in the subsoil, about 80 cm apart,’ says Dr Sale. ‘Then we’re following it up with a winter crop whose roots proliferate around the amendment,, and it seems that the roots then do the transformative work between the rip-lines for us.’
Nutrients in the organic matter, plus the crop roots and soil microorganisms, all work together to make the soil sponge-like so it can absorb and hold water.
‘We’re using poultry litter from the broiler sheds where meat birds are grown,' Dr Sales explains. 'These birds spend their short life on wood shavings or rice hulls that get rich with excreta, and that’s what we’re using.’
Results are encouraging. All the team's trials have resulted in an average increase in crop yields of 60 per cent across the Victorian high-rainfall cropping zone.
Now, the research is attracting attention and harvesting significant financial backing from the grains industry.
Resilience in a changing climate
As the climate gets warmer, challenges to food production will increase.
There'll be intense wet periods and extended dry periods. And when it’s wet, we’ll need soil that retains as much water as possible so crops can use it to grow when the season is dry.
As Dr Sale says, 'soil is not a renewable resource. We need to protect and improve it so it can work for us in the long term. It’s about building resilience in crop production – in our food production. Because we’re producing staples here: staple cereals.’
The team is looking at making the process of converting subsoil cheaper and faster. Grain farms are often remote from manure sources, so the technology needs to be accessible.
For Professor Tang, the importance of this work can't be underestimated.
‘Soil is not a renewable resource,' he says. 'We need to protect and improve soil so it can work for us in the long term, rather than degrade the soil and pass it on to the next generation in a poorer condition. Proper soil management also makes the agriculture system more sustainable.’
For Dr Sale, the passion of the students working on the La Trobe project says it all.
Together, they're working towards a sustainable future – not just for our benefit, but for generations to come.
Dr Peter Sale is Reader, Associate Professor in the School of Life Sciences at La Trobe University.
Professor Caixian Tang is also based in the School of Life Sciences, in the Department of Animal, Plant and Soil Sciences.
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