What it is
Breaking up soil that has been compressed into a layer roots cannot penetrate.
Compaction forms two ways. Heavy machinery (tractors, livestock, construction) crushes pore space between soil particles. Over-tillage smears wet ground into a hard plough pan 20 to 30 cm down. The result is the same: a slab of dense earth that water cannot infiltrate and roots cannot cross.
A penetrometer reading above 2.5 megapascals stops most root growth. Compacted pasture often reads 3.5 to 4.5 MPa at the pan. Concrete reads about 20.
Why it works
Roots need oxygen. So do the fungi, bacteria, and earthworms that build soil. A compacted layer is anaerobic below the first few centimetres. Nitrogen-fixing bacteria suffocate. Mycorrhizal networks cannot extend. Earthworm populations collapse.
Water cannot move either. Rain hits the surface, pools, and runs off. Topsoil washes away. Subsoil stays dry through the wet season and bone-hard through the dry. The land turns into a shedding system instead of a storing system.
Fracture the pan and the system restarts. Air gets in. Water sinks. Roots follow. Earthworms recolonise from the edges. Within two seasons you can move soil bulk density from 1.7 g/cm³ back toward 1.3, which is the threshold most pasture grasses need to thrive.
Match the method to the scale
Garden bed (under 100 m²). Broadfork. Two-handled fork with 30 cm tines. Step it in, rock back, lift, move 15 cm forward, repeat. No soil flipping. No layer mixing. One person can decompact a 50 m² bed in an hour. Pair with no-dig afterwards and you only do it once.
Small farm (1 to 20 ha). Subsoiler or single-tine ripper behind a tractor. Run 40 to 50 cm deep on contour. Slow forward speed, 4 to 6 km/h, so the tine shatters the pan rather than slicing through it. Work when soil is just below field capacity, never wet.
Landscape scale (20 ha plus). Keyline plough (Yeomans plough). P.A. Yeomans developed it in 1950s Australia. The shank fractures subsoil without inverting the surface. Run on the keyline pattern (see keyline design) so water spreads from valleys toward ridges. Yeomans built 6,500 ha of pasture from bare red dirt to grazed grass in under a decade at his Yobarnie property.
Run it
Test before you commit. Push a 40 cm steel rod into damp soil. If it stops at 20 cm under hand pressure, you have a pan. Dig a 60 cm pit and look at the profile. A grey, mottled, or dense band confirms it.
Time it right. Soil must be moist but not wet. Bone-dry ground bounces under the tine and shatters the equipment instead of the pan. Saturated ground smears and re-seals as soon as the implement passes.
Work on contour, always. Down-slope ripping creates instant erosion channels. Mark the contour first (see swales for A-frame and bunyip methods).
Pass once, plant the same season. An open pan re-closes in two to three years under heavy rain and stock pressure. The only durable fix is biology. Deep-rooted plants take the gap and hold it open.
Deep-rooted decompactors. Tillage radish (Raphanus sativus) sends a 60 cm taproot through residual pan in one season. Sunflower hits 1.5 m. Sweet clover (Melilotus alba) reaches 2 m by year two. Comfrey, chicory, and lucerne (alfalfa) all break and hold structure. Plant them in mix as a cover crop over freshly ripped ground.
Pair with organic matter building. Mulch, compost, and chop-and-drop residues feed the soil food web, and biological structure outlasts mechanical structure every time.
When it goes wrong
Pan returns in two seasons. No biology followed the rip. Plant deep-rooted cover within four weeks of decompaction, and again after each grazing or cropping cycle.
Erosion after ripping. You ran off-contour, or you left the surface bare too long. Re-seed immediately. On slopes over 8 percent, combine ripping with check dams or swales.
Tractor sinks. Soil was too wet. Stop. Wait two weeks. Try again. Ripping wet ground does more compaction damage than it fixes.
No yield response. Compaction may not have been the limit. Run a soil test for nutrients and pH. Decompaction fixes structure, not chemistry.