Subsoiler

How it works

Most cultivators work the top 15 to 20 cm. Over years, heavy wheels and repeated ploughing at the same depth can create a dense pan just below. A subsoiler runs its legs, also called tines or shanks, a little below that pan. A hardened point at the foot of each leg lifts and shatters the compacted soil, and wings on either side of the point widen the loosened zone without bringing subsoil to the surface.

The soil must be dry enough to crack. In wet conditions the legs simply smear a slot through it, which can make drainage worse. Many subsoilers carry a disc in front of each leg to cut trash and a packer roller behind to firm the surface.

Main types

• Straight-leg subsoiler: Traditional heavy vertical legs. Effective, but they lift more soil and disturb the surface.
• Low-disturbance subsoiler: Curved or angled legs with a low lift angle that crack the pan while leaving the surface and crop residue largely intact. Popular in min-till and grassland work.
• Bent-leg or paratill type: Legs bent sideways that fracture the soil below the surface with less power per leg.
• Grassland subsoiler: Slim legs and front discs to relieve compaction under pasture with little surface damage.
• Mole plough: A related tool with a torpedo-shaped foot that forms drainage channels in clay. It is not a subsoiler.

Hooking it up to a tractor

Most subsoilers mount on the three-point linkage, using the lower links for depth; larger trailed models use depth wheels. Legs are held with shear bolts or auto-reset springs so they survive stones. Power demand is high: about 40 to 50 hp per leg is a common planning figure, and more in very hard ground, so a three-leg unit suits a tractor of 120 hp or more, while five and seven-leg machines need 200 to 350 hp. Each extra 5 cm of depth can nearly double the pull needed.

Before you subsoil

Advisers urge caution: subsoiling soil that is not compacted can damage good structure. Dig a few holes in suspect areas such as gateways and headlands, look for roots growing sideways, platy soil or a sudden change in moisture, and use a penetrometer on moist soil to find the depth of the pan. Then set the points just below it, usually only a few centimetres deeper than the problem.

Buying and care tips

• Space legs by depth: Winged legs are usually spaced around two to two and a half times their working depth so the loosened zones meet.
• Dig after a test run: After a short run, dig across the work to check the soil has cracked rather than smeared.
• Choose auto-reset in stony ground: Spring or hydraulic reset saves endless shear bolts.
• Get roots in quickly: Sow a crop or cover crop soon after so roots hold the new structure, and keep heavy traffic off.
• Check points and wings: Replaceable wear parts on used machines are often worn short, reducing depth and effect.

Questions people ask

What does a subsoiler do?

It breaks up compacted layers below normal cultivation depth so roots can grow deeper and water can drain.

How deep should a subsoiler go?

Just below the compacted layer, which you find by digging or with a penetrometer. Going deeper wastes fuel and can harm good soil.

When is the best time to subsoil?

When the soil is dry enough to shatter, often late summer or early autumn before the ground gets wet.

What is the difference between a subsoiler and a mole plough?

A subsoiler shatters compacted soil to loosen it. A mole plough pulls a bullet-shaped foot through clay to form drainage channels.

Related equipment

Sources

1. Subsoiler, Wikipedia
2. 7 steps to successful subsoiling, Farmers Weekly
3. Dry fall gives a window to alleviate soil compaction, Penn State Extension

Last checked 2026-11-01

← All equipment