A subsoiler or mole plough is a tractor mounted implement used to loosen and break up soil at depths below the level of a traditional disk harrow or rototiller. Most tractor mounted cultivation tools will break up and turn over surface soil to a depth of 6" to 8" while a subsoiler will break up and loosen soil to twice those depths. Typically a subsoiler mounted to a Compact Utility Tractor will reach depths of about 12" and typically have only one thin blade with a sharpened tip.
The subsoiler is a tillage tool which will improve growth in all crops where soil compaction is a problem. 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 24" depths.
Various manufacturer's brochures claim that crops perform well during hot and dry seasons because roots penetrate soil layers deeper to reach moisture and nutrients. Brochures further claim that in wet conditions, the water passes easier through the shattered areas, reducing the possibility of crops drowning.
Agricultural tractors will have multiple deeper reaching blades; each blade is called a scarifier or shank. Purdue University's Dept. of Agriculture indicates that common subsoilers for agricultural use are available with 3, 5 or 7 shanks. These units can be up to 15' wide, some models are towed behind tractors, others are tractor mounted to the 3pt hitch.
A form of this implement (with a single blade), a pipe-and-cable-laying plough, is used to lay buried cables or pipes, without the need to dig a deep trench and re-fill it.
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