Special feature: Subsoil aerators vs aerators

Date: 22.09.2022

A closer look at the difference between subsoil aerators and aerators and why it matters

Often when agricultural landowners first become interested in subsoil aeration due to the many benefits it offers, a common point of confusion can be around figuring the difference between a ‘subsoil aerator’ and an ‘aerator’ and how they differ in application and final result.

Ultimately, the difference is in the one single additional word ‘subsoil’, so let’s see what that means.

The Oxford dictionary describes subsoil being, "The layer of soil between the surface of the ground and the hard rock below it." Or according to many agricultural-based research institutes, it’s the horizons below the working depth of 300mm. The exact depth of the subsoil will vary from farm to farm, but what’s clear is that it’s well below the working reach of most conventional tillage methods. And therein lies the issue – a layer of soil that gradually compacts over time and goes on to restrict root growth of pastures and crops leading to reduced yields, with most conventional tillage methods focused on upper soil layers. 

What this means for a farmer

It’s not subsoil aeration if the implement does not reach beyond the start of the subsoil horizon (minimum of 200–300mm, depending on soil type)

If it doesn’t remove subsoil compaction, it’ll still be there, meaning top-soil aeration and conventional tillage operations will only bring short-term benefit, as underlying subsoil compaction remains and will impede further root and plant growth once the roots reach that layer

To remove subsoil compaction, the aerator/subsoiler needs to reach the subsoil

So, what’s the confusion?

Many become confused between ‘aerators’ and ‘subsoil aerators’ believing they do the same job but, in fact, they do not.

Subsoil aeration is the method of aerating that actually reaches deep into the subsoil. The difference between these two styles of aerators is a subsoil aerator uses shanks/legs that penetrate down into those lower layers, with a foot that provides a lift as it runs through the ground. This upward-lifting effect creates fractures in the soil, making it more permeable, thereby removing compaction and making the soil looser.

The practice of subsoiling is typically referred to as "the process of soil tillage performed by a tool inserted into the soil to a depth of at least 350 mm." A subsoil aerator will reach deep into the subsoil layers to fracture the soil structure enabling greater water, air, and moisture flow through all soil layers it’s working in. Whereas most soil aerators will only work the topsoil due to a lack of working depth, not to mention the irony of claiming to fix compaction by forcibly rolling spikes into the ground.

If you have subsoil compaction issues on your farm, it’s important to make sure you correctly identify the causes (prevention is better than cure) and ensure you have a full understanding of the scope of the compaction issue in your pastures/paddocks before beginning any remediation. Only then will you really know what options are going to deliver the best result.

Some common symptoms of subsoil compaction include:
• Water ponding
• Shallow roots
• Low fertiliser response

For more information about subsoil aeration benefits and the most suitable machinery to suit your specific needs – from the Rata 304 to the Rata Panerazer for tractors over 120hp – contact the New Zealand family business Rata and their in-house team of experts.

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