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Soil and life

Soil Analysis

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

A soil auger in the slope, a bucket with a mixed sample and empty sample bags

In brief

Laboratory measurement of a soil sample: pH, humus, nutrients, lime, salt and sodium, ideally read together with field tests such as the spade test.

What is a soil analysis?

A soil analysis is the laboratory measurement of a soil sample. The sample is dried, sieved to remove everything coarser than two millimetres, and then examined with standardised methods. What comes back is a sheet of numbers that describe what the soil contains: how acid or alkaline it is, how much of the main nutrients plants can draw on, how much organic matter it carries, whether it holds lime, salt or too much sodium.

The usual parameters:

  • pH: acidity or alkalinity on a scale where 7 is neutral. It decides how available most nutrients are, and which plants feel at home. Many nutrients are most accessible in the slightly acid to neutral range.
  • Humus or organic carbon: usually determined as organic carbon and converted to humus. It is the most important figure for anyone who wants to follow soil improvement over the years.
  • Nitrogen: as total nitrogen, often together with the ratio of carbon to nitrogen, which shows how readily organic matter decomposes. Mineral nitrogen fluctuates within days and is only meaningful for specific questions.
  • Phosphorus, potassium, magnesium: the classic plant nutrients of a standard analysis.
  • Trace elements: boron, copper, manganese, zinc, iron and others, measured when deficiency symptoms appear or before planting crops with special needs.
  • Lime: the carbonate content. Calcareous soils buffer acidity but can lock up iron and phosphorus.
  • Salt and sodium: electrical conductivity shows dissolved salts, the exchangeable sodium share shows whether sodium is breaking down the soil structure. A classic American reference work from 1954 sets the thresholds still used today: soils with high conductivity count as saline, those with more than 15 percent exchangeable sodium as sodic. Both matter near the coast and wherever brackish water is used for irrigation.
  • Texture and exchange capacity: a laboratory particle-size analysis confirms or corrects texture by feel, and the cation exchange capacity says how many nutrients the soil can hold at all.

Methods differ between countries. Italy's official methods for soil chemistry were laid down by ministerial decree in 1999, Germany follows the method book of its agricultural research institutes. Results are only comparable if the same method was used.

A lab report is only as,good as the sampleLearning panel: a lab report is only as good as the sample, because a few hundred grams have to stand for a whole area. Composite sample: on a slope keep upper, middle and lower sections apart, because soil moves downhill; take at least 15 cores in a W or X pattern; leave out edges, paths, fire sites, compost heaps and fresh manure. Keep the same depth, for example arable land 15 to 20 centimetres, grassland 10, fruit trees down to about 30. Mix all cores in a clean bucket and take a few hundred grams. Label with place, depth and date, keep out of the sun, never dry it in an oven. The report shows pH, humus as the key figure for following the years, nitrogen, phosphorus, potassium and magnesium, trace elements, lime, salt and sodium with the threshold of 15 percent exchangeable sodium, texture and exchange capacity. Results are only comparable if the same method was used. One analysis is a snapshot, a series is evidence: the same areas, the same depth, the same season, the same method. TERRAWIKI · LEARNING PANEL A lab report is only asgood as the sample A few hundred grams have to stand for a whole area. 1TAKING A COMPOSITE SAMPLE upper middle lower Separate the sectionsupper, middle and lower apart:soil moves downhillAt least 15 coresin a W or X patternLeave outedges, paths, fire sites,compost heaps, fresh manure 102030 cm Same depth e.g. arable 15 to20 cm, grassland 10,fruit trees toabout 30 cm Mix all cores in aclean bucket, takea few hundredgrams Label place, depth, date;keep out of the sun,never dry it inan oven 2WHAT THE REPORT SHOWS LAB REPORT pHacidity, 7 is neutralHumusthe key figure for following the yearsNitrogentotal, often with the C:N ratioP, K, Mgthe classic plant nutrientsTrace elementsfor deficiencies or special cropsLimebuffers acidity, can lock up iron, phosphorusSalt, sodiumconductivity shows salts; over 15 percentexchangeable sodium counts as sodicTextureconfirms or corrects texture by feelExchange capacityhow many nutrients the soil can hold Results are only comparable if the same method was used. 3A SERIES IS EVIDENCE One analysisa snapshot A seriesevidence the same areas, the same depth,the same season, the same method Basis: LfL Bayern, Anleitung zur Bodenprobenahme (2022) · TerraWiki: Soil Analysis

When an analysis pays off

An analysis is worth its cost when its result changes a decision. That is the case before permanent plantings such as orchards or groves are established, because mistakes in pH or salt can no longer be corrected cheaply once the trees stand. It is the case before liming or fertilising, so as not to give what the soil already has. And it is the case when plants struggle and neither the spade test nor the plants around them explain why.

A second reason is the baseline. Anyone who wants to show that humus is building up in a soil needs a starting value, measured with a method that will still be used years later. A single analysis is a snapshot; a series is evidence.

An analysis pays off less when nobody will act on it, or when the sample is so poorly taken that it represents no particular part of the land.

How to take a composite sample

The weakest link in any soil analysis is not the laboratory but the sample. A few hundred grams have to stand for a whole area, so they must be gathered from many places.

  1. Divide the land. Areas that differ in soil, use or management are sampled separately. On slopes, upper, middle and lower sections are kept apart, because soil is moved downhill.
  2. Choose the right moment. The soil should be moist but not smearing, and the sample should be taken before fertilising, not shortly after.
  3. Take many cores. At least 15 small cores or thin slices per sample, spread over the area in a W or X pattern. Edges, paths, old fire sites, compost heaps and spots under fresh manure are left out.
  4. Keep the depth constant. The Bavarian guidance, for example, samples arable land to 15 to 20 centimetres and grassland to 10. For fruit trees, the Hessian state laboratory recommends slices down to about 30 centimetres. Before planting deep-rooted trees, a second sample from below that depth can be useful.
  5. Mix and pack. Mix all cores thoroughly in a clean bucket, take a few hundred grams, put them in a labelled bag with place, depth and date. Keep the bag out of the sun and never dry it in an oven.
  6. Ask for the method. Agree with the laboratory which package and which methods it uses, and stay with them for later analyses.

How Terra Humana understands it

For Terra Humana the laboratory complements hand and eye; it does not replace them. A soil read first with the fingers and the spade is sampled more sensibly, because one knows where it changes. And the laboratory sheet is read more sensibly when it can be laid next to the field notes.

We also treat its numbers with care. A single value says little about a living soil that changes with the seasons. What counts is the series: the same areas, the same depth, the same season, the same method, over many years. That is how humus becomes visible as something that grows, rather than as a figure on a page.

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

Sa Medada

What this looks like at Sa Medada

There is no laboratory analysis of the soil at Sa Medada yet. The land is a slope with old terraces, and a slope is sampled in sections rather than as one mixture, with upper, middle and lower parts kept apart. Until the analysis exists, texture by feel and the spade test give the first reading. The analysis will then set the baseline against which every later change in the soil can be measured.

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Frequently asked

What does a soil analysis measure?

A standard analysis usually covers pH and the main plant nutrients phosphorus, potassium and magnesium, often with an estimate of soil texture. Extended packages add humus or organic carbon, total nitrogen and the ratio of carbon to nitrogen, lime content, trace elements such as boron, copper, manganese, zinc and iron, and the cation exchange capacity, a measure of how many nutrients a soil can hold. In dry regions and near the coast, electrical conductivity for salt and the share of sodium are worth adding. Which parameters make sense depends on the question you want answered.

How do I take a soil sample for the laboratory?

Not as a single spadeful, but as a composite sample. Walk across a uniform area in a W or X pattern and take at least 15 small cores or thin slices, all from the same depth, avoiding edges, paths, compost heaps and old fire sites. Mix them thoroughly in a clean bucket and send a few hundred grams in a labelled bag. Areas that differ in soil, slope position or use are sampled separately. The soil should be moist but not smearing, and the sample must never be dried in an oven.

How often should soil be analysed?

For gardens and orchards, advisory services in Germany usually recommend an analysis every three to five years, ideally at the same season and always with the same method, so that the results can be compared. A first analysis is most valuable before establishing permanent plantings such as trees, before liming or fertilising, and whenever plants show symptoms that field observation cannot explain. An analysis repeated over years becomes a record of whether the soil is gaining or losing humus.

Can a laboratory analysis replace field tests?

No, the two answer different questions. The laboratory measures what the soil contains: acidity, nutrients, salt, organic carbon. It says little about how the soil is built, whether water can enter, whether roots meet a compacted layer, whether soil life is active. That is what texture by feel, the spade test and indicator plants show. The most reliable picture comes from combining both, and field tests also help decide where a laboratory sample is worth taking.

Why do pH values from different laboratories differ?

Because pH can be measured in different solutions. German laboratories usually measure it in a calcium chloride solution, Italian official methods mainly in water, and the value in water tends to be somewhat higher. Phosphorus is also extracted with different methods depending on country and soil, for example Olsen for neutral to calcareous soils and Bray for acid soils, and the numbers are not directly comparable. The result sheet should always state the method, and comparisons over time only make sense with the same one.

Wattle fences and sprouting willow cuttings securing a steep bankNext in this themeSoil BioengineeringHolding slopes and banks with living plants as building material, from willow cuttings to brush layers, often combined with stone or timber.

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.A block of soil lifted out beside the spade hole, with crumbly topsoil, roots and a denser layer belowSpade TestA block of soil is dug out with a spade and examined on the spot for crumbs, roots, earthworms, smell and compacted layers.A grazed, stony pasture in spring overrun by flowering asphodelIndicator PlantsWild plants whose presence reveals the moisture, acidity, nutrient supply, light or salt of a site, so that the vegetation can be read like a soil report.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.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.Hands holding porous pieces of biochar above dark soilBiocharA stable, charcoal-like material made by heating plant matter with little oxygen, mixed into soil to improve its structure, water-holding and living activity.

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Sources

  • LfL Bayern, Anleitung zur Bodenprobenahme, based on VDLUFA Methodenbuch I, method A 1.2.1 (2022)
  • Landesbetrieb Hessisches Landeslabor, Probenahme Gartenboden (2024)
  • Ministero per le Politiche Agricole, D.M. 13 settembre 1999, Metodi ufficiali di analisi chimica del suolo, G.U. n. 248 (1999)
  • U.S. Salinity Laboratory Staff, Diagnosis and Improvement of Saline and Alkali Soils, USDA Agriculture Handbook 60 (1954)
  • FAO, Guidelines for Soil Description, 4th edition (2006)

Last updated: 2026-10-12