The challenge
Many Australian agricultural soils contain multiple physical and chemical constraints that limit effective root growth which limits water and nutrient use by crops. As a result, yields are significantly less, resulting in major opportunity costs for growers.
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.
Subsoil constraints are likely to have large effects on the how much water crops need. Quantifying how subsoil constraints affect a crop’s ability to use soil water is important for productivity and water-use efficiency, because yield is linked to transpiration.
Our research
The overall purpose of this project was to achieve reliable and profitable crop productivity in soils with multiple constraints and to close the gap between farm production and the rainfall-limited crop yield potential in major soil types in Victoria (Vic), New South Wales (NSW), Queensland (Qld) and Western Australia (WA).
Four on-farm field experiments were established to assess the long-term effectiveness of new practices and products to ameliorate multiple soil constraints in representative soil types. The key constraints were dispersive, alkaline poorly structured subsoils in Vic and NSW, dense sodic subsoils in Qld, and low water holding capacity and water repellent sands in WA.
Amendments being tested in this project include custom-made organic matter (OM)-based pellets (e.g. lucerne straw, oaten hay), nutrient-enriched urban green-waste compost, agrisilica, various reactive clays, and sugarcane mill mud/ash. Amendments were placed directly into the subsoil using customised deep rippers, chisel ploughs and other heavy-duty tillage implements.
Data from the project was made available to Soil CRC projects 4.3.005 and 4.3.006 to enable data on crop production and water use efficiency (WUE) to be better modelled and described, with potential benefits to yield (yield, reliability of yield, water stress resilience) being weighed against cost of implementation.
The project also has direct engagement with Soil CRC Program 1 to maximise adoption of the project outcomes. The main goal is for maximum adoption of results/techniques to benefit local grower groups, and Australian farmers more broadly.
Objectives
Aim 1: To establish on-farm field experiments to assess the long-term effectiveness of new practices and products to ameliorate multiple soil constraints in key soil types that support the grains and sugarcane industries.
Aim 2: To quantify the effectiveness of different amelioration strategies to increase soil water storage and crop water use efficiency.
Aim 3: To assemble datasets for use by next users in calibration and validation of hybrid biophysical modelling to develop frameworks and tools for diagnosing and ameliorating multiple soil constraints.
Results
To establish on-farm field experiments to assess the long-term effectiveness of new practices and products to ameliorate multiple soil constraints in key soil types that support the grains and sugarcane industries.
Four new field trial sites were successfully established on working farms near: Clare, Qld, on a heavy sodic clay soil of the Burdekin River Irrigation Area; Lockhart, NSW, on an alkaline, dispersive, sodic heavy clay soil in the Riverina cropping area; Wonwondah, Vic, on a poorly drained, highly dispersive sodic Vertosol in the Wimmera broadacre cropping region; and Kweda, WA, on a duplex sandy soil with low pH and multiple subsoil constraints, including aluminium (Al) toxicity, low fertility and water logging, in the WA grain belt.
Due to the length of sugarcane crop growth cycles, the Qld trial was established later than the other sites and has only recently completed its first year. Monitoring of this site under project 4.2.004 was extended until 30 September 2025.
To quantify the effectiveness of different amelioration strategies to increase soil water storage and crop water use efficiency.
Results from the four trial sites to date have been mixed, with two sites largely unresponsive (Qld and WA) and the other two (NSW and Vic) showing some significant crop responses to some amelioration strategies.
Effects from subsoil amelioration are at times not seen in the first year following amendment application, so the lack of treatment effects found at the Qld site may simply be because the amendments have not had sufficient time to have an impact on the soil constraints that are present.
The WA site has had average to above average rainfall, and this may have caused the crop to be less affected by the soil constraints at that site in terms of crop water-limited yield potential. The results from the NSW and Vic sites both indicate that the presence of nutrient-rich OM in the ameliorants had the greatest impact on crop performance compared to mineral-only treatments and the controls. Increases in crop yield in the second year of these two sites from OM-based treatments were up to 19% above the untreated control at the NSW site, and an average of 42% greater than the untreated control at the Vic site. The 2023 NSW site wheat crop and Vic site canola crop on the OM-based treatment plots were both able to access substantially more soil water than the other treatments.
At this stage it cannot be concluded whether the comparative effectiveness of these ameliorants in improving crop productivity is due to improved nutrition, better soil physicochemical conditions, or a combination of both mechanisms.
To assemble datasets for use by next users in calibration and validation of hybrid biophysical modelling to develop frameworks and tools for diagnosing and ameliorating multiple soil constraints.
Data from the four trial sites has been supplied to the Agricultural Systems and Catchment modelling team in the University of Southern Queensland’s Centre for Sustainable Agricultural Systems. The modelling team are using the Agricultural Production Systems sIMulator (APSIM) model to assess the impact of subsoil constraints on WUE and crop production (Soil CRC projects 4.3.005; 4.3.006).
By calibrating and testing the model using field trial data from this project and other Soil CRC field experiments, the team hope to evaluate promising amelioration techniques in computer modelling simulations, explore the long-term impacts of subsoil constraints and predict crop responses under varying conditions, including future climate change scenarios.
Next steps
The WA, NSW and Qld sites will continue to be monitored under Soil CRC project 4.2.006, ‘Capitalising on established field trials for ameliorating (sub)soil constraints‘.
Dig deeper
Read the project final report and research findings fact sheet to find out more.
