Soil Strength Following Amelioration: Year Two Results

By Kate Parker, WMG Project Officer

Soil amelioration is often viewed as a long-term investment, and results from the Creagh site in Dandaragan are starting to show what growers can expect in the years following treatment. Penetrometer testing, which measures how deep roots can grow before hitting soil strength limitations, was conducted at the site in both 2024 and 2025. Alongside these tests, root samples were taken from each treatment to provide a clearer picture of crop establishment below the soil surface.

Soil Strength: What Has Changed?

In the first year following amelioration (2024), penetrometer testing showed a clear advantage for treated plots compared with the controls. Control plots reached the threshold where root growth becomes limited (around 2500 kPa) at just 150 mm, while ameliorated treatments, particularly the Nufab double pass and the Fanger plow, allowed roots to penetrate well below 250 mm.

Testing in 2025 largely confirmed these patterns. While soil strength increased higher in the profile, an expected result of natural reconsolidation, ameliorated plots continued to support deeper root penetration than controls. The Nufab treatments again performed strongly, with roots able to extend to nearly 200 mm before encountering limiting resistance. The Fanger and Plozza plough treatments followed closely, reaching depths of around 150 mm. In contrast, controls remained limited to shallow depths of approximately 100 mm.

This pattern fits with expectations: amelioration often provides the biggest gains in the first year, but many of the benefits can persist into subsequent seasons, even as soils naturally firm up again.

Root Growth: What We Can See Below the Surface

Images of lupin roots collected in July 2025 supported the penetrometer findings. In ameliorated plots, roots were longer and displayed well-developed lateral spread, forming more structurally intact root systems. In contrast, control plots showed shallow root systems with roots closely following the taproot, reflecting the difficulty of penetrating compacted soil layers.

In particular, the Nufab and Plozza treatments supported lateral root growth throughout the profile, suggesting improved access to both subsoil moisture and nutrients. These differences in root architecture are important because they underpin crop resilience. Crops with deeper and more extensive root systems are better positioned to access water during dry periods and to make more efficient use of applied fertilisers.

What Does This Mean for Farmers?

For growers weighing up the costs and benefits of soil amelioration, the Creagh results provide reassurance that the investment can pay off beyond the first season. Although soil reconsolidation does occur, treatments such as the Nufab double pass and the Fanger plow continue to improve rooting depth and soil structure into the second year.

It is important, however, to recognise that responses vary depending on soil type, seasonal rainfall, and paddock management. At the Creagh site, the benefits have been most noticeable in gravelly sand profiles, where shallow root growth is usually a major limitation. Ongoing monitoring over the next seasons will show whether these establishment gains translate into yield benefits.

For now, the key message is clear: soil amelioration can deliver lasting improvements in root development and soil function. To maximise returns on investment, growers should pair amelioration with careful observation and adaptive management tailored to their soil type and seasonal conditions.

This information piece was developed as part of the GRDC-funded Soil Water Repellence Project. For more information on the project and local trial results, visit the project page.