subsoiler or flat lifter is a tractor-mounted farm implement used for deep tillage loosening and breaking up soil at depths below the levels worked by moldboard ploughs, disc harrows, or rototillers. Most such tools will break up and turn over surface soil to a depth of 15–20 cm (5.9–7.9 in), whereas a subsoiler will break up and loosen soil to twice those depths.

The subsolier is a tillage tool which will improve growth in all crops where soil compaction  is a problem. In agriculture angled wings are used to lift and shatter the hardpan  that builds up due to compaction. The design provides deep tillage, loosening soil deeper than a tiller or plough is capable of reaching. Agricultural subsoilers, according to the Unverferth Company, can disrupt hardpan ground down to 60 cm (24 in) depths.

The subsoiler consists of three or more heavy vertical shanks (standards) mounted on a toolbar or frame with share bolts. They can be operated at depths of 45–75 cm (18–30 in) or more. A ripper normally runs 35–45 cm (14–18 in) deep. Subsoiling is a slow operation and requires high power input: 60 to 100 hp to pull a single subsoil point through a hard soil.

Typically, a subsoiler mounted on a compact utility tractor will reach depths of about 30 cm (12 in) and have only one thin blade with a sharpened tip.  The points of the shanks are normally about 30 cm (12 in) wide and should be easy to replace. The condition of the points is very important: often the subsoiler fails to give good results due to the condition of its points. Points can be fitted with horizontal wings, about 30 cm (12 in) wide, which considerably increases the width of soil below ploughing depth loosened by the subsoiler.