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ENDEIT
Soil and life

Spade Test

Terra Humana editorial teamLast updated: 2026-10-127 min read

A block of soil lifted out beside the spade hole, with crumbly topsoil, roots and a denser layer below

In brief

A block of soil is dug out with a spade and examined on the spot for crumbs, roots, earthworms, smell and compacted layers.

What is a spade test?

A soil analysis tells you what a soil contains. A spade test shows how it is built. It looks at the topsoil the way roots and water meet it: as a structure of crumbs, pores and channels that is either open or closed. For that, a block of earth is cut out with a spade, lifted, broken apart by hand and examined on the spot. Laboratory equipment is not needed, and the whole test takes less than half an hour per site.

The method has roots in German farming practice, in the Spatendiagnose of Johannes Görbing. Building on later versions of it, in her 2003 dissertation at the University of Giessen, Andrea Beste refined it into a method with clear criteria that can be compared between sites. In New Zealand, Graham Shepherd developed Visual Soil Assessment along similar lines, in which every observation is scored against reference photographs. In 2008 FAO adapted it into field guides for several crops, among them olive orchards, together with the University of Teramo.

The spade test belongs together with texture by feel. Texture says what a soil is made of; the spade test shows what has become of that material through management, roots and soil life. Unlike texture, everything it records can change, and that is what makes it useful: it can register an improvement or a decline within a few years.

What the block on,the spade revealsLearning panel: what the block on the spade reveals. Analysis tells what a soil contains, the spade shows how it is built. Method: dig when the soil is moist but not wet, in the Mediterranean the wet season, as dry summer ground is too hard. Choose spots that represent the area, plus a reference spot under undisturbed vegetation. Dig a pit about 20 by 20 centimetres and 30 centimetres deep, run a knife down the wall and note where it meets resistance. Cut a spade-wide block, about 20 centimetres each way, place it on a sheet and break it along its cracks without force. An open soil shows rounded, porous crumbs, evenly spread roots, worms, channels and casts, brown colour that is darker on top from humus, and smells earthy. A closed soil shows sharp-edged clods and plates, roots that bend sideways, a hard pan with an abrupt boundary, grey patches and rust mottles, and smells sour or rotten. The FAO guide rates more than 30 earthworms per block as good; on dry Mediterranean ground the comparison of the same spot over the years matters more. The same spot, dug at the same season each year and photographed, shows whether the soil is opening up or closing. Where there is compaction, roots and soil life do the loosening over time, not machines, and the surface stays covered. TERRAWIKI · LEARNING PANEL What the block onthe spade reveals Analysis tells what it contains. The spade, how it is built. 1HOW IT IS DONE 1 At the right time Moist but not wet: in the Mediterranean the wetseason. Dry summer ground is too hard. 2 Spots and a reference Spots that represent the area, plus a referencespot under undisturbed vegetation. 3 Pit and knife A pit about 20 by 20 cm, 30 cm deep. Run a knifedown the wall and note where it meets resistance. 4 Cut the block Spade-wide, about 20 cm each way, onto a sheet;break it along its cracks without force. 2OPEN OR CLOSED Open rounded, porous crumbsroots spread evenlyworms, channels and castsbrown, darker on top: humussmells earthy Closed sharp-edged clods, platesroots bend sidewayshard pan, abrupt boundarygrey patches, rust mottlessmells sour or rotten Earthworms: the FAO guide rates more than 30 per block as good.On dry Mediterranean ground, comparing the same spot over theyears matters more than the absolute number. The same spot, dug at the same season each year andphotographed, shows whether the soil is opening up or closing. Where it shows compaction, we do not dig deeper with machines.Roots and soil life do the loosening over time, and the surfacestays covered while they do. Basis: Shepherd et al., VSA Olive Orchards, FAO (2008) · TerraWiki: Spade Test

How it is done

The soil should be moist but not wet. The FAO guide's check is to roll a thread about five centimetres long and four millimetres thick; if that succeeds easily, wait. In the Mediterranean that means the wet season. Dry summer ground is too hard and tells you little.

Choose spots that represent the area, and add a reference spot under undisturbed vegetation, at a field edge or under a hedge. The comparison often says more than any single result.

First dig a small pit about 20 by 20 centimetres and 30 centimetres deep, and run a knife down the side wall from top to bottom. Where it suddenly meets more resistance, note the depth. Then cut a block about the width of the spade, roughly 20 centimetres in every direction, lift it out on the blade and place it on a sheet or tarpaulin. The FAO guide drops the block from about one metre onto a firm board up to three times, so that it falls apart along its natural cracks. Pulling it apart gently by hand works as well, as long as no force is used.

What you see

  • Structure: rounded, porous crumbs of varied size are a good sign. Sharp-edged, smooth-faced clods, flat plates or large dense blocks without visible pores indicate a damaged structure.
  • Roots: fine roots spread evenly through the block, also downwards. Roots that bend sideways, grow flattened or only follow cracks have hit a barrier.
  • Earthworms and channels: count the worms and look for their channels and casts. The FAO guide rates more than 30 worms per block as good; its scale comes from wetter climates, so on dry Mediterranean ground the comparison of the same spot over the years matters more than the absolute number. Worms retreat deep into the soil in the dry season, which is another reason to dig in winter.
  • Colour and mottles: brown, yellowish or reddish tones indicate good aeration, darker tones near the surface indicate humus. Grey or blue-grey patches and rust-coloured mottles show where water stands and air is missing.
  • Smell: earthy is good. Sour, musty or rotten means a lack of oxygen.
  • Surface: loose and crumbly, or sealed and crusted after rain.
  • Transitions: an abrupt boundary between loose soil above and a hard layer below is the classic sign of a compacted pan, for example where a plough has run at the same depth for years.

How Terra Humana understands it

For Terra Humana the spade test is less a single verdict than a series of observations. The same spot, dug at the same season each year and photographed, shows whether the soil is opening up or closing. It is honest in a way that suits restoration work: a measure that looks successful on the surface does not count as a success while the block on the spade still shows dense clods, bent roots and no worms.

It also keeps the attention where the work happens. Ground cover, mulch and deep-rooted plants are meant to build crumbs and channels; the spade test is how we check whether they do. Where it shows compaction, it tells us not to dig deeper with machines, but to let roots and soil life do the loosening over time, and to keep the surface covered while they do.

The valley of Sa Medada near Jerzu, Sardinia, with olive grove and macchia

Sa Medada

What this looks like at Sa Medada

Sa Medada lies on the eastern side of Sardinia, with a dry season from May to September. In those months the ground is too hard for a meaningful spade test, so its time is the wet season, when the soil is moist without smearing. Project Eden begins with pioneer plants, ground cover and holding water. Whether the cover is working shows first in the block of soil on the spade: in its crumbs, its roots and its worm channels.

More about Project Eden

Frequently asked

What is a spade test?

A spade test is a field method for judging the condition of the topsoil with nothing more than a spade, a knife and a sheet to work on. A block of soil is cut out, lifted, broken apart by hand and examined: how it falls apart, whether the crumbs are round and porous or sharp-edged and dense, how the roots run, how many earthworms and worm channels it holds, what colour it has and how it smells. The method goes back to the German Spatendiagnose of Johannes Görbing and has been developed into scored field guides, among them FAO's Visual Soil Assessment.

When is the best time for a spade test?

When the soil is moist but not wet, the state in which it could be worked. The FAO field guide offers a simple check: roll a little soil into a thread about five centimetres long and four millimetres thick. If the thread forms easily, the soil is too wet; if it cracks first, the time is right. In a Mediterranean climate that means the wet season, after the first autumn rains and before the ground dries out in late spring. In midsummer the soil is too hard to show anything meaningful.

What does a healthy soil block look like?

It breaks into rounded, porous crumbs of different sizes when dropped or pulled apart gently. Fine roots run through it evenly in all directions, including downwards. Worm channels and worm casts are easy to find. The colour is brown, often darker near the surface, without grey or blue-grey patches. And it smells earthy, the scent produced by soil microorganisms. A good block also shows no abrupt boundary where loose soil suddenly gives way to a hard layer.

How do I recognise soil compaction in a spade test?

By resistance and by what the roots do. Push a knife into the side of the pit from top to bottom: where it suddenly meets much more resistance, there is a dense layer. Roots that bend sideways at that depth, grow flattened or only follow cracks confirm it. Compacted soil breaks into large, sharp-edged clods or plates instead of crumbs, has few pores and few worm channels, and often shows grey patches with rusty mottles where water stands and air is missing.

What does the smell of soil tell you?

More than most people expect. A pleasant, earthy smell comes largely from geosmin, a substance released by soil bacteria of the actinomycete group, and indicates an active, well aerated soil. A sour, musty or rotten smell points to a lack of oxygen, usually because water stands in a compacted or sealed layer and organic matter decomposes without air. A soil that smells of almost nothing is often simply poor in life and organic matter.

A soil profile in a manioc field by the Amazon: a deep black layer full of charcoal and pottery shards above pale subsoilNext in this themeTerra Preta (Amazonian Dark Earth)Dark, human-made soil of the Amazon, built up over centuries from charcoal, ash, bones, pottery and household waste, and still fertile today.

Related terms

Hands pressing moist soil between thumb and fingers into a thin ribbonTexture by FeelEstimating a soil's share of sand, silt and clay by rubbing, rolling and pressing moist earth between the fingers, without a laboratory.Crumbly, living soil next to a dense, smooth clod of compacted earthSoil StructureThe way soil particles are arranged into crumbs and the pores between them. It decides how a soil breathes, takes in water and lets roots through.Deep tractor ruts in a wet field where rainwater stands instead of soaking inSoil CompactionThe loss of pore space through pressure, from machines, hooves or feet. Compacted soil lets less water and air in and blocks roots.A cut through living topsoil with roots, white fungal threads and an earthworm beneath a layer of leavesSoil Food WebAll the organisms living in soil, from bacteria and fungi to mites and earthworms. Together they digest dead matter and turn it into food for plants.Hands holding dark, crumbly soil with fine rootsHumusThe dark, stable fraction of organic matter in soil, the part that holds water and nutrients and gives a living soil its colour, smell and structure.A soil auger in the slope, a bucket with a mixed sample and empty sample bagsSoil AnalysisLaboratory measurement of a soil sample: pH, humus, nutrients, lime, salt and sodium, ideally read together with field tests such as the spade test.

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Sources

  • Andrea Beste, Weiterentwicklung und Erprobung der Spatendiagnose als Feldmethode, dissertation, University of Giessen (2003)
  • G. Shepherd, F. Stagnari, M. Pisante and J. Benites, Visual Soil Assessment Field Guide: Olive Orchards, FAO (2008)
  • T. G. Shepherd, Visual Soil Assessment, Volume 1, 2nd edition, Horizons Regional Council, New Zealand (2008)
  • Hochschule Geisenheim, Spatenprobe / Spatendiagnose, after B. Ziegler, Bodenpflege im Weinbau (2012)

Last updated: 2026-10-12