A subsoiler is an agricultural machine used to loosen deeply compacted soil without fully turning the soil over. It is pulled by a tractor and uses strong narrow shanks to fracture hardpan layers below the normal plowing depth. This matters because compacted soil restricts root growth, water infiltration, and air movement.
Better soil structure can improve crop resilience, especially during drought or heavy rain.
Key Facts
- Draft force is the pulling force needed to move the subsoiler through soil.
- Work done by the tractor is W = Fd, where F is draft force and d is distance traveled.
- Power required is P = Fv, where F is draft force and v is travel speed.
- Typical subsoiling depth is about 30 cm to 60 cm, depending on crop needs and soil conditions.
- Shanks should usually run below the compacted layer so the hardpan fractures upward and sideways.
- Subsoiling is most effective when soil is dry enough to crack but not so dry that draft force becomes excessive.
Vocabulary
- Subsoiler
- A tillage implement with deep shanks designed to loosen compacted soil below the usual plow layer.
- Hardpan
- A dense compacted soil layer that limits root penetration, drainage, and air movement.
- Shank
- A strong curved or straight metal tine that penetrates the soil and lifts it to create cracks.
- Draft force
- The horizontal pulling force required for a tractor to move an implement through soil.
- Soil compaction
- The squeezing together of soil particles, which reduces pore space for water, air, and roots.
Common Mistakes to Avoid
- Running too shallow, because the shanks may pass above the hardpan and leave the compacted layer mostly unchanged.
- Subsoiling when the soil is too wet, because wet soil tends to smear and deform instead of cracking into a looser structure.
- Using too many shanks for the tractor size, because draft force and power demand can exceed the tractor's safe pulling capacity.
- Assuming subsoiling is needed every year, because unnecessary deep tillage can waste fuel, disturb soil biology, and increase erosion risk.
Practice Questions
- 1 A tractor pulls a subsoiler with a draft force of 18,000 N for 250 m. How much work is done on the implement?
- 2 A subsoiler requires a draft force of 24,000 N while moving at 1.8 m/s. What power is required in watts and kilowatts?
- 3 A field has a compacted layer at 25 cm depth and the subsoiler is set to 20 cm. Explain why this setting may not improve root growth much, and describe a better adjustment.