How to Observe and Assess Your Soil, and Where to Find Public Data

Key takeaways

• Start with your eyes, hands and a spade: dig a block of moist soil and look at crumbs, plates, roots, colour and life.
• Texture can be felt or estimated with the jar test, and drainage and infiltration can be watched after rain.
• Compare a site with what it could be, a similar soil under good management or its own earlier condition, before calling it degraded.
• Use a laboratory when you need measured values, such as for salinity, pH or nutrient planning, or when site history suggests contamination.
• Public soil maps are a good first guess, but they are made at a scale and date that may not match your plot, so check them against your own observations.

How do you start with your eyes, hands and a spade?

You do not need a laboratory to learn a great deal about soil. A spade, a bucket, a jar, a ruler and some patience will reveal texture, structure, drainage, rooting and biological activity. These observations cannot replace chemical analysis, but they tell you what questions to ask, and they are the only way to understand how the soil behaves on the ground, which a lab report cannot capture.

Where and when should you look?

Soil varies across a field or garden, so look in more than one place. Compare a healthy-looking area with a poor one, a slope with a hollow, a track with a quiet corner, and a cultivated patch with an undisturbed edge such as a hedge or fence line. The best time is when the soil is moist but not saturated, perhaps a day or two after rain has soaked in. Record the date, weather and location of every observation so that you can repeat it later and see change.

The spade test

Dig a clean block of soil about as deep as the spade blade and lay it on a tarp or board. Then look and feel.

• Layers and colour: note the dark topsoil and where it gives way to paler subsoil. A thin or patchy dark layer can indicate loss or low organic matter. Grey, blue or orange mottles suggest waterlogging.
• Structure: gently break the block along natural lines. Rounded, crumbly aggregates are a good sign. Flat plates, large sharp-edged clods or a solid massive block suggest compaction or poor structure.
• Roots: look at how deeply and freely roots grow. Roots that turn sideways, bunch up or stop at a hard layer point to a barrier.
• Life: look for earthworms, burrows, fungal threads, insects and decomposing residue. Few signs of life in what should be a moist, vegetated soil is worth noting.
• Smell: a pleasant earthy smell is normal. A sour or rotten-egg odour suggests oxygen-starved, waterlogged soil.

Feel for texture

Texture describes the relative proportions of sand, silt and clay. Take a small handful of moist soil and knead it until it behaves uniformly. Try to roll it into a ball, then a ribbon between thumb and finger.

• If it will not hold together, it is mostly sand and feels gritty.
• If it forms a ball but breaks when you try to make a ribbon, it is a loamy or sandy loam type.
• If it forms a long, flexible ribbon and feels sticky and smooth, clay is dominant.
• If it feels silky or floury, silt is prominent.

Texture does not change quickly, so it is useful for understanding limits: sandy soils drain fast and hold few nutrients, while clay soils hold water and nutrients but compact and waterlog easily.

The jar test

Fill a clear straight-sided jar about one third with soil, top it up with water, add a teaspoon of dish detergent to help particles separate, and shake thoroughly. Let it stand. Sand settles within a minute or so, silt settles over some hours, and the finest clay may take a day or longer to clear. The thickness of each layer gives a rough idea of proportions. It is approximate, but it helps confirm what the hand feel suggests.

Check drainage and infiltration

Push a bottomless can or a length of pipe into the ground, fill it with water and watch how long it takes to soak away. Repeat after the first fill, since the second reading reflects the soil when already wet. Very slow infiltration suggests crusting, compaction or heavy clay, while extremely fast drainage may point to coarse sand or large cracks. Compare different spots, and compare wheel tracks with undisturbed ground. You can also dig a small hole, fill it with water, and see whether water is still standing in it the next day after rain.

Reading the surface and the site

Walk the area after heavy rain. Look for muddy runoff, silt fans, small channels, pale patches and exposed roots. Check for salt crusts on dry ground and for bare patches ringed by tolerant plants. Follow water from the highest point to the lowest and notice where it speeds up, concentrates or ponds, since problems at the bottom of a field are often fed from somewhere above.

• Compare soil under a fence line, hedge or woodland edge with the cultivated ground beside it. The difference shows what has changed.
• Check soil height against old fence posts, tree bases or stone walls, which can reveal long-term loss or build-up.
• Stripes in crop vigour often follow tracks and compaction, circular bare patches may mark salt or old pollution, and weak growth on knolls often indicates eroded topsoil.
• Learn the indicator plants of your area, such as salt-tolerant species, moisture-loving rushes or acid-favouring weeds.
• Ask about history. Old maps, aerial photographs and long-time neighbours can reveal former industry, drainage works or changes in crop.

Photograph the same points each season from the same position. Repeat photos are a surprisingly powerful record of change.

Simple field tests

• pH kits and meters: inexpensive and useful for a rough reading, though quality and calibration vary. Use them as indicators rather than final answers.
• Penetration probe: a metal rod pushed into moist soil reveals firm layers by the change in resistance.
• Slake test: place a dry crumb in clear water and watch whether it holds together or collapses into cloud. Rapid collapse suggests weak aggregates or sodicity.
• Residue burial test: bury cotton fabric for a few weeks and see how much has been broken down, as a crude sign of biological activity.

When should you get laboratory testing?

Observation tells you what is wrong in broad terms; laboratory analysis tells you how much and what to do. Consider testing when:

• You are planning to grow food and want to set fertiliser and lime programmes sensibly.
• You suspect salinity, sodicity or low pH and need measured values.
• The site has a history of industry, fuel storage, heavy traffic, treated timber or waste, or you are building a vegetable garden or children's play area in an urban setting.
• Crops show symptoms you cannot explain.
• You want a baseline to track progress over time.

Taking a good sample

Results are only as good as the sample. Follow the laboratory's instructions, use clean tools and containers, and avoid sampling right after fertiliser or lime applications or in unusual spots such as fence corners. Collect several cores across a defined area at the same depth, mix them, and send a representative portion. Keep distinct areas separate if they differ in soil type or management. Choose accredited laboratories where possible, state what you want measured, and keep the same method and depth each time so results are comparable.

Which check for which question

Question	Simple check	When to use a laboratory
Is the structure good or compacted?	Dig a spade-sized block of moist soil and break it apart; push a thin rod in to find firm resistance	Rarely needed; structure is judged on site
What is the texture?	Feel the soil, or shake it with water in a jar and let it settle	When you need exact proportions
Does water drain and soak in?	Watch for ponding and runoff after rain and dig a small hole to look at roots	Rarely needed
Is it salty, acidic or short of nutrients?	Look for white crusts, patchy crops and use a home kit for a rough pH	For measured pH, salinity and nutrients
Could the site be contaminated?	Review its history: industry, fuel, heavy traffic, waste or old buildings	Always, using an accredited laboratory and a proper sampling plan

Where can you find public soil data?

You may not need to start from nothing. In many countries, public bodies publish information that describes the soils of a region. Look for national or regional soil surveys, geological surveys, agricultural and environmental agencies, universities, and international organisations that compile soil maps and databases. Typical products include soil maps with descriptions of each soil type, interpretation guides covering drainage, erosion risk and suitability for different uses, land capability classifications, geological and topographic maps, historic aerial photographs, and, in some places, monitoring programmes that sample soils repeatedly over time. FAO's soils portal lists soil maps and databases and national soil information systems in its data hub, and ISRIC's SoilGrids offers global digital soil maps at 250 metre resolution covering fourteen soil properties at six standard depth intervals, so a single mapped cell is far larger than a garden.

When using maps, remember their limits. They are made at a particular scale, so a small garden may differ from the mapped unit that contains it, and the information may be decades old in places. Treat map units as a good first guess and check them against what you find with your spade. Local advisory services, conservation districts, extension officers and land-care groups can often interpret this material and point you to testing laboratories.

Keep a simple soil journal

Record what you did, what you saw, weather, crops and results. A journal turns scattered observations into evidence, helps you spot trends in structure, drainage and plant performance, and tells you whether your management is working or needs to change.

Sources and further reading

• FAO Soils Portal: Data hub: the portal's data hub, which lists soil maps and databases and national soil information systems.
• ISRIC: SoilGrids: the global digital soil maps of ISRIC World Soil Information: 250 metre resolution, fourteen soil properties, six standard depth intervals.

Frequently asked questions

What is the easiest way to check soil structure?

Dig out a spade-sized block of moist soil and break it gently apart. Rounded, crumbly aggregates are a good sign, while flat plates or hard clods suggest compaction.

How does the jar test work?

You shake soil with water and let it settle. Sand drops first, then silt, then clay, and the relative thickness of the layers gives a rough picture of texture.

When is a laboratory test really necessary?

Test when you need measured values, such as for salinity, pH or nutrient planning, or when the site history suggests possible contamination, especially before growing food or building play areas.

Where can I find soil maps for my area?

Look for national or regional soil surveys, geological surveys, agricultural or environmental agencies and universities. Maps are a good first guess, but always check them against your own observations.