Many Australian crops are not reaching the potential yields for the rainfall they receive because the soils in which they grow have physical and chemical constraints, usually in the subsoil, that are limiting root growth. This limits a plant’s access to water and nutrients. This reduction in yield represents major opportunity losses for growers.
Our ‘Integrated solutions for accessing soil moisture’ project (4.2.004) helped to quantify crop responses to different soil management practices, on key soils across 4 cropping regions. The project started in 2022 and was a collaboration between the NSW Department of Primary Industries and Regional Development, Agriculture Victoria, Murdoch University, Charles Sturt University and Burdekin Productivity Services.
Understanding how subsoil conditions affect a crop’s ability to access water is an important step in improving both productivity and water use efficiency, as transpiration is linked to crop yields.
“The ability of roots to grow through soil unhindered by physical or chemical constraints is key to making full use of the available water resources,” said Dr Murray Hart, Soil CRC Project Leader and Research Officer at the NSW Department of Primary Industries and Regional Development.
Long-term sites enable testing of multiple variables
The project established 1 medium-term and 3 long-term (5-plus years) trial sites: Wonwondah in Victoria (medium-term site), Lockhart in New South Wales, Clare in Queensland and Kweda in Western Australia.
The Wonwondah and Lockhart sites are constrained by alkaline, poorly structured subsoils, while the Clare site has dense sodic subsoils, and the Kewda site is affected by water repellent sands and low water holding capacity.
All 4 sites are putting recent advances in soil amelioration techniques into practice, to enhance understanding of how these techniques can improve crop rooting depth, water use, productivity, and ultimately yield.
Between them, the sites have been testing amelioration effects on sugarcane, and broadacre crops such as barley, lupin, faba bean, canola and wheat. Novel soil amendments were applied directly into the subsoil, targeted at individual constraints at each site. The table below highlights some of the amendments that were applied at each site.
Findings from the sites to date have been varied. The Kweda and Clare sites were largely unresponsive to treatment, while the Wonwondah and Lockhart sites showed large treatment effects to some of the amendments.
A benefit of long-term sites is that practices can be tested over multiple seasons, with some ameliorants not showing benefits in their first application. It also allows the benefits of soil biological processes to be evaluated, which may contribute to a range of positive outcomes. This is often the case for soils with constraints including sodicity causing soil dispersion – where soil structure collapses when wet.
It also allows for techniques to be tested in different weather conditions. High rainfall can reduce the impact of soil constraints, so understanding how soil will respond to these conditions can help growers be more efficient with ameliorant application.
Addressing subsoil amelioration is complex
Climatic conditions have a huge impact on amendments. In dry conditions, especially in early growth stages, a lack of moisture can prevent amendments from improving soils. If conditions are much wetter than average, crops may not be water-limited and can effectively bypass otherwise significant constraints.
Initial results indicated that organic matter ameliorants have the potential to improve water use and crop productivity for sodic, clay soils in Victoria and New South Wales – provided they have a minimum carbon to nitrogen ratio. It is too early for the effectiveness of the ameliorants to be attributed to improved nutrition, better physiochemical conditions or a combination, but ongoing testing will provide further insights.
Capitalising on established field sites
The Kweda, Lockhart and Clare trial sites will continue to be monitored under a follow-on Soil CRC project, ‘Capitalising on established field trials for ameliorating (sub)soil constraints’ (4.2.006), which began in 2024. A further 3 sites from other Soil CRC projects will also be extended under the project.
Led by Professor Richard Bell from Murdoch University, the project will continue investigations for 2 more cropping seasons. This will enable the capture of more data on climate variability, as well as economic analysis of outcomes.
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Main image (top): Attendees at a farm walk investigating trial plots in Lockhart, NSW. Source: Dr Murray Hart, NSW DPIRD