Practice

Subsoiling

Also known as: deep ripping, chisel plowing (deep)

A tillage practice that uses a narrow, deep-running implement to fracture compacted soil layers below the topsoil — typically 30–60 cm deep — without inverting the soil profile. Used to break hardpan compaction (often plow-pan from prior tillage), improve drainage and root penetration, and prepare degraded soil for transition to no-till or perennial cover. A one-time or infrequent intervention rather than annual practice; over-use reverses the soil-structure benefits it's meant to create.

Practical

A subsoiler — typically a single shank or set of shanks pulled by a tractor — runs through [[soil|the soil]] at depth, fracturing compacted layers without flipping the surface horizon. Surface residue and topsoil structure stay largely intact; the disturbance is below ground.

When it makes sense:

Plow-pan compaction — a hard layer at typical tillage depth (~15–20 cm) caused by years of moldboard or disc plowing.
Heavy-equipment compaction — vehicle traffic, especially on wet soil, creates dense layers that roots and water can’t penetrate.
Pasture renovation — long-term pasture under grazing animals can develop sub-surface compaction; subsoiling re-aerates without destroying pasture sward.
Drainage improvement — fractured soil drains faster, reducing waterlogging without needing tile drainage on borderline sites.

When it backfires:

Wet soil — running a subsoiler through saturated soil smears rather than fractures, creating a worse compaction layer.
Annual repetition — repeated subsoiling structures [[soil|the soil]] to need it; the practice should be a transitional tool, not a permanent input.
Over-aerated sand — already-loose soils don’t need fracturing; subsoiling there just destroys aggregate structure.

Scientific

Soil compaction is a measurable property: bulk density above ~1.6 g/cm³ for loams and ~1.8 g/cm³ for sands restricts root growth. Compaction reduces water infiltration, decreases aeration, suppresses microbial activity, and concentrates surface runoff. Subsoiling fractures the compacted layer without inverting the horizon; [[soil|the soil]] profile rearranges, water and roots access deeper layers, and biological activity resumes at depth.

The Yeomans Plow — developed by P.A. Yeomans in Australia in the 1950s as part of the Keyline System — is the canonical regenerative subsoiler. Run on a slight off-contour pattern that moves water from valleys toward ridges, the Yeomans Plow combines deep ripping with hydrological restructuring of the landscape.

Cultural

In [[industrial-agriculture|conventional agriculture]], subsoiling is treated as routine annual tillage; in [[regenerative-agriculture|regenerative agriculture]], it’s a one-time transition tool deployed when no-till adoption requires legacy compaction relief. Mark Shepard’s Restoration Agriculture and Joel Salatin’s writings on pasture renovation both reference subsoiling as a corrective.

Lenses still to grow

The Yeomans Plow specifically as an instrument
Comparative effects of moldboard, chisel, and Yeomans subsoiling on soil-microbiome continuity
Cover-crop deep-taproot species ([[tillage-radish|daikon radish]], sunn hemp, alfalfa) as biological subsoilers
Compaction measurement tools (penetrometer, bulk density sampling)

Sources

Yeomans, The [[keyline-design|Keyline Plan]] (1954) and Water for Every Farm (1965)
[[mark-shepard|Mark Shepard]], Restoration Agriculture
USDA-NRCS Soil Quality technical notes on compaction
Brady & Weil, The Nature and Properties of Soils (textbook reference)

Rooted in life.

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