Dig First, Rip Later: Why Testing to Depth Matters Before Soil Amelioration

Jun 20,2025 Broadening Article, Soil Amelioration Project, 2025, Projects, RAD2406,

By Kate Parker & Simon Kruger, WMG

More WA growers are turning to mechanical soil amelioration such as spading, delving or inversion ploughing to address water repellence, acidity and compaction. Before bringing heavy machinery into the paddock, there is one essential step that should not be skipped: testing your soil to depth.

It might not be as eye-catching as watching machinery in action, but understanding what is happening beneath the surface can make the difference between a successful result and an expensive mistake.

What’s the Risk?

Although a paddock may appear uniform from the top, soils can vary significantly just 20 or 30 centimetres down. Differences in structure, texture or chemistry can affect how a soil responds to disturbance. If a machine is going to dig, mix or invert soil, it is critical to know what layers it will interact with.

Without deep testing, growers risk:

Bringing up subsoil that is sodic, acidic or saline
Mixing gravel or poor-quality material into the topsoil, reducing seedbed quality
Misjudging the depth of water-repellent layers, resulting in under- or over-treatment

These issues often emerge after sowing. Patchy germination, poor vigour or localised waterlogging may not be apparent until it is too late to intervene.

This variation in response is not just theoretical. A 2024 GRDC GroundCover article based on the West Midlands Group led Ripper Gauge Project reported that outcomes from WA soil amelioration trials ranged from a $620 per hectare gain to a $656 per hectare loss, depending on how well the subsoil constraints were understood and managed. The article’s key takeaway was clear: soil amelioration needs to be customised for each site.

What Does ‘Testing to Depth’ Involve?

Proper testing means collecting samples in layers, often every 10 or 20 centimetres, to assess how soil properties change with depth. These samples can be analysed in the lab or assessed in the field using practical methods if the operator is confident in interpretation.

Key things to examine include:

Texture: transitions from sand to clay, or the presence of gravel or compacted layers
pH and salinity: acidic or saline zones below the surface
Structure and moisture: whether the soil is hard-setting, compacted or dispersive

The Soil Quality Knowledge Base recommends that soil be tested to the planned working depth of amelioration to avoid unexpected constraints and to guide investment decisions.

Variation in soil makeup and structure in a 90cm deep soil core.

Where and When to Test

It is not necessary to sample every hectare. Choosing representative areas or known problem spots provides a useful guide. Yield maps, electromagnetic (EM) surveys and visual observations can help prioritise where to dig. Case studies show that EM surveys are particularly effective for identifying the depth to clay or gravel layers, which can help determine whether to spade, delve, clay or invert.

Testing should be done before deciding on an amelioration approach or setting machinery depth. GRDC guidelines advise that without a clear picture of soil profile limitations, there is a real risk of selecting the wrong treatment or applying it at the wrong depth.

Why It’s Worth the Effort

Amelioration is a costly and time-sensitive operation. Testing to at least 30 centimetres, and often 50 centimetres, in 10 centimetre increments is recommended by GRDC as a way to identify the best return on investment. Including analysis of pH, texture, salinity and structural properties ensures the treatment is guided by reliable data.

A small investment in testing can:

Prevent unintended harm to crop establishment and yield
Help match machinery type and settings to soil profile conditions
Improve crop outcomes and long-term productivity

Before you commit to deep ripping, delving or inversion, take the time to assess what lies beneath. The best results start with informed decisions, and the best decisions come from understanding your soil.