Key points
- Sandy soils can be found on more than 16 million hectares of agricultural land in Australia (excluding Queensland and the Northern Territory), 51% of which are in Western Australia.
- Soil amendment (ripping, delving, spading, inversion ploughing) suitability maps have been developed for sandy soils. These provide a useful basis for further validation, refinement and development.
- Amendments such as zeolite and hydrotalcite helped retain water and minimised nutrient loss via leaching from sands. Composts can also improve water retention, but they may lead to significant nutrient loss since sandy soils still lack the ability to hold onto those added nutrients.
The challenge
Sandy soils cover more than 16 million hectares across Australia. Their fundamental limitation is their low reactive surface area, caused by low clay and organic matter content. This restricts their ability to retain water and nutrients, making it difficult to meet crop and pasture demands.
Sandy soils often suffer from multiple constraints, including nutrient deficiencies, acidity, dense packing, low water-holding capacity, poor fertiliser use efficiency, and water repellence. They are also prone to nutrient leaching and degradation through acidification, subsoil compaction, and erosion. Calcareous sands share many of these problems but are further limited by high alkalinity.
One of the most promising approaches to improving sandy soils is to increase their reactive surface area by adding clay, stable organic matter, or both. These amendments target the underlying constraint — poor water and nutrient retention. However, the conditions under which these amendments are most effective remain poorly understood, and not all sandy soils are the same, making it difficult to predict when and where soil amelioration techniques will deliver reliable benefits.
Our research
We began by refining the national understanding of sandy soil distribution. Using soil-landscape databases from New South Wales, South Australia, Tasmania, Victoria and Western Australia, we produced an updated map showing the extent of sandy soils in agricultural regions (Figure 1).
To support better decision-making around soil amelioration, a sandy soil suitability assessment framework was developed. This tool helps match different sandy soil profiles with appropriate amendment approaches — such as spading, ripping, delving or inversion ploughing. The framework was tested using Western Australian soils as a case study.
A national meta-analysis brought together data from 270 field trials across South Australia, Western Australia, Victoria and New South Wales. These trials measured changes in crop biomass, yield and soil organic carbon following soil amendment with clay and/or organic matter. The aim was to identify patterns in how sandy soils respond to clay and organic amendments, and to understand the conditions under which they are effective.
Pot experiments assessed how novel amendments influence nutrient leaching and plant growth in sandy soils. Leaching trials tested how different soil amendments influenced water retention and nutrient loss in sandy soils under low irrigation. Amendments included compost (pelletised and ground), zeolite (rock and ground), spongolite and a polymer product (Rescaype), applied at rates equivalent to typical field applications.
Plant growth trials using ryegrass examined how selected amendments affect early plant development and nutrient uptake (Figure 2). Amendments included calcium bentonite, hydrotalcite, activated biochar, compost, and a compost-clay blend. Trials were conducted with uniform nutrient and water supply, and amendments were applied at rates typical of field conditions. Amendments were incorporated either at the surface, through the full soil profile, or placed below the root zone.
Research findings
National sandy soils map
A revised map of sandy soils in agricultural regions of five states (excluding Qld and NT) increased the estimated area of sandy soils from 11 to 16 million hectares. This map is now accessible through the Visualising Australasia’s Soils portal (https://data.soilcrc.com.au/map).
Sandy soil suitability assessment framework
The sandy soil suitability assessment framework identifies where different mechanical amendment methods — spading, delving, ripping and inversion ploughing — are likely to be most effective, based on soil profile characteristics. When applied to Western Australian soils, where much of the research on these methods has taken place, it categorised sandy soils based on features that affect amendment success, such as the depth of the sand layer and the presence of subsoil constraints.
The framework provides a practical means to help growers and advisers select appropriate amelioration strategies and highlights areas where further ground-truthing and refinement are needed. With refinement, this framework could help guide on-farm investment in soil re-engineering to alleviate constraints.
Meta-analysis of field responses to sandy soil amendment
The meta-analysis revealed that crop yield in sandy soils increased with surface soil organic carbon (SOC) concentrations between 0.75 and 1.5%. Below 0.75%, there was no yield response, possibly indicating a threshold for basic soil function. Above 1.5%, yield gains plateaued, suggesting that other factors may be limiting productivity or the stabilisation of added organic inputs.
Seasonal rainfall patterns had a strong influence on SOC levels. Higher SOC was associated with rainfall in autumn, winter and spring, while a higher proportion of summer rainfall tended to reduce SOC, likely due to faster decomposition under warm and moist conditions.
Mineral nitrogen was linked to improved productivity, while organic nitrogen correlated with higher SOC levels and greater microbial biomass. Additions of nitrogen, phosphorus and sulphur further increased SOC, but only when existing surface SOC exceeded 1.5%. The analysis also suggested that iron and calcium may help stabilise SOC by improving aggregation and reducing microbial decomposition.
The concentration of clay in amended sands influenced the outcome. A surface clay content between 6 and 10% supported optimal productivity, but yields declined when clay exceeded 15%. However, while adding more clay continued to increase soil organic carbon, it also led to reduced yields — highlighting a trade-off between building soil carbon and maintaining productivity.
No single soil characteristic could predict the success of soil amendments. Responses varied depending on local constraints such as water repellence, water-holding capacity, soil pH, amendment rate, incorporation depth and the depth of sand over clay. The findings emphasised the need to address multiple limitations when designing amendment strategies.
To accurately assess the long-term effects of amendments, we recommend sampling soils to a depth of at least 30 cm and repeating measurements regularly over five to twenty years. This is particularly important given the lag between productivity gains and measurable increases in organic carbon.
Pot trials
Under glasshouse conditions, zeolite showed strong potential to reduce nutrient leaching and improve water retention in sandy soils. Applied at 20 t/ha, both ground and rock forms increased water retention under low irrigation. Zeolite consistently reduced losses of nitrogen, phosphorus and potassium, with ground zeolite retaining more ammonium and rock zeolite retaining more nitrate. It was the most effective amendment tested for reducing overall nutrient loss.
Compost also improved water retention and reduced nitrogen leaching, but it led to higher losses of potassium, calcium, magnesium, sulphur, iron and sodium due to its high nutrient content. Ground compost leached more than pelletised compost, indicating that particle size influences nutrient retention. The effectiveness of compost varied depending on the nutrient and formulation.
These results suggest zeolite is a reliable amendment for reducing nutrient loss, while the effectiveness of compost depends on both particle size and the specific nutrient.
Other amendments, including spongolite and the Rescaype polymer, had little impact on water or nutrient retention. Hydrotalcite showed promise under high leaching risk and may warrant further investigation.
In the ryegrass trials, amendments did not significantly affect plant growth but did influence nutrient uptake. This suggests that under ideal conditions (water and nutrients not limiting), the benefits of amendments may be limited. A larger South Australian Research and Development Institute (SARDI) study confirmed that most growth responses were due to nutrients supplied by the amendments themselves.
Amendment placement was also important. Incorporation into the top 9 cm or throughout the 0-18 cm profile improved nutrient response by aligning with the root zone. Deeper placement or inter-row application had little effect, likely due to limited root contact. To maximise benefit, amendments should be placed in or near the root zone.
Significance of findings
The revised sandy soils map and amendment suitability framework will allow researchers, advisers and growers to better target where amendments are needed and what types may be effective. The mapping is accessible on the Visualising Australasia’s Soils portal (https://data.soilcrc.com.au/map). Because soil amelioration is a significant investment, choosing the right amendment for each soil type is critical. Applying the wrong treatment can lead to high costs with little benefit—evidence-based decisions are essential as more farmers adopt these practices.
The meta-analysis brought together a large and diverse body of field data, revealing patterns not visible in individual trials. It provides a stronger evidence base for designing amendment strategies suited to different conditions, helping shift decision-making from trial-and-error to informed, targeted approaches. It also highlights where future research and monitoring efforts should be focused to address remaining knowledge gaps.
Glasshouse experiments confirmed that the effectiveness of amendments depends not just on the material used, but also on its placement. Surface or full-profile incorporation near the root zone improved nutrient availability, whereas deep or off-row placement had little benefit. This has practical implications for machinery setup and amendment incorporation during field operations.
The glasshouse experiments also showed that many observed benefits of amendments were due to the nutrients they supplied rather than changes in soil structure. This challenges assumptions about amendment function and reinforces the need to evaluate both short-term nutrient effects and long-term structural changes.
Next steps
The next step is to select the most promising of the novel amendments and continue to investigate the effects when water and nutrient supply is limited, to better reflect their potential benefits in rainfed agricultural situations. The recommended amendments are zeolite, hydrotalcite, clay-compost, and lucerne pellets.
Two long-term field trials with novel amendments on sandy soils have been established and will be maintained through to 2028 with support from the Soil CRC. These sites will be sampled at the end of 2027 to assess changes in soil organic carbon, with results expected in 2028.
The amendment suitability assessment framework should be refined into a grower-facing decision support tool. Validation with experts, site audits, and Agricultural Production Systems sIMulator (APSIM) modelling will be needed to improve accuracy and support long-term adoption.
Selected sites from the meta-analysis should be revisited to assess the longevity of amendment effects on yield and soil carbon. Further analysis of the database could improve understanding of how amendments affect nutrient retention and availability.
Sandy soil mapping should be expanded to Queensland and the Northern Territory and refined to align with the updated Australian Soil Classification Arenosol soil order.
