Soil Health Testing: 6 Key Indicators

Soil health testing is fundamental to know your soil and how to take care of it. In the Soil Lab at Mud Valley Foundation we recommend a fundamental set of 6 different indicators for soil health testing over a time. These indicators were chosen as the set of minimum tests you can do to get critical soil health information about your soil without depending on a laboratory. They measure the physical, chemical, and biological aspects of soil. These are important because the physical and biological functions of soil influence key chemical functions, such as nutrient availability. Healthy soil is the foundation of thriving gardens and productive veggie beds.

These indicators can be found in the Ecosystem Restoration Communities Soil Framework (ERCSF) and are the key indicators used in the Horizon Europe ECHO soil testing program, for which Mud Valley Foundation is an ambassador.

The 6 fundamental soil health testing indicators are:

– soil texture (physical) ERCSF Indicator #1,

– soil structure and aggregate stability (physical) ERCSF Indicator #2,

– soil water infiltration (physical) ERCSF Indicator #7,

– soil pH (chemical) ERCSF Indicator #8,

– biological activity in soil (biological) ERCSF Indicator #9,

– and soil organic matter (SOM) (biological) ERCSF Indicator #15.

Below you will find all the details for each indicator – what they are, why it matters, how to test for it, and what you will learn from the results.

Everyone interested in improving soil health should have in mind that soil management practices change soil slowly over time. By monitoring changes in soil properties over time, early signs of soil degradation such as erosion or compaction, or soil regeneration such as a gain of organic matter can be detected and fixed.

Soils should be tested at similar times each year (ideally during the spring) using the same methods in order to accurately measure changes in the soil over time. It is important to repeat these tests every year for at least for 5 years and ideally up to 10 years.

First, a representative soil sample is collected from the field, typically using a shovel. You can select the location(s) according to what land use(s) or practice(s) you adopted which you want to measure the impact of. Ideally, you will do the soil sampling 2-3 days after a good rain event so that the soil is moist but not soaked; digging will be easier, as is performing the soil testing. It will also be more relevant as soil life will be more active in the spring in these conditions.

At each sampling point, first remove the roots and plants aboveground, and then dig out a 30x30x30 centimeters cube of topsoil. You will be able to complete all of the soil health tests indicated below with this same sample.

Using your senses

• The smell of the soil may be an indicator of soil health.
  • Soils that support abundant populations of bacteria or fungi may have an “earthy” odor associated with their presence. Close your eyes, smell, and… are you in a forest after rain?
• The color of a soil can also be indicative of its condition.
  • Soils with poor drainage and reduced oxygen levels will appear grayish instead of more commonly brown, black (high content of organic matter), or red (iron oxides-rich) soils.

What is it

Soil texture describes the proportion of sand, silt, and clay in your soil. This influences how soil drains, holds nutrients, and behaves overall.

Why it matters

• Sandy soils drain fast but hold few nutrients.
• Clay soils retain nutrients but may have poor drainage.
• Loam soils (balanced texture) are ideal for most plants and soil life.

The feel test uses touch and ribboning. The feel test is a qualitative method, as it does not provide exact values of sand, silt, and clay.

The ribboning technique involves moistening a soil sample to form a ball or ribbon to estimate texture based on coherence and ribbon length.

1. Moisten the soil until it feels like dough.
2. Rub it between your fingers and try to form a ribbon by squeezing it between thumb and forefinger.

• Soils that have a high percentage of sand, such as sandy loam or sandy clay, have a gritty texture. Sandy soils won’t form a ribbon.
• Soils that have a high percentage of silt, such as silty loam or silty clay, feel smooth and soft, forming a short ribbon.
• Soils that have a high percentage of clay, such as clay loam, have a sticky feel and easily form a long ribbon.
• Loam soils (ideal) are a balanced mix: slightly gritty, slightly smooth, forming a short ribbon.

This method visually shows how much sand, silt, and clay you have in your soil sample.

How to do it

You will need a clear jar with a lid and water (+ dish soap) per soil sample.

1. Fill the jar ⅓ with soil. Remove sticks, roots, and stones.
2. Add water until nearly full. Add a few drops of dish soap.
3. Shake vigorously for 1–2 minutes.
4. Set the jar down and let it settle for at least 24 hours.
5. Observe and measure the layers in the jar: at the bottom, sand, in the middle, silt, and at the top, clay.
6. You will use the texture triangle diagram to interpret your results. It provides a rough estimate on the percentages of sand, silt, and clay in the soil.

• Sandy soil drains fast but dries quickly.
• Clay soil holds nutrients but drains poorly.
• Loamy soil (ideal) is a balanced mix.

What it is

Soil structure is how particles clump together into aggregates. It is a key indicator of soil functioning and health as it affects root growth, water flow, and microbial life. Two complementary tests can be used and scores are given based on size, shape, and stability of aggregates.

Why it matters

• Good structure includes crumbly, stable aggregates.
• Poor structure includes compaction, crusting, and runoff.

How to do it

1. Drop the soil sample a maximum of three times from a height of one metre (approximately waist height) onto the firm base of your container. If large clods break away after the first or second drop, drop them individually again once or twice. If a clod shatters into small units after the first or second drop, it does not need dropping again. Do not drop any piece of soil more than three times.
2. Transfer soil on top of a large plastic bag or sheet.
3. Organize the aggregates by size; move the coarsest parts to one end and the finest to the other end to obtain a measure of the aggregate-size distribution.
4. Compare your distribution of aggregates with the three photographs below.

• Good structure = Score 2 (left image): Soil aggregates break into a few medium pieces. Good distribution of finer aggregates with no significant clodding.
• Moderate structure = Score 1 (middle image): Soil contains significant proportions of both coarse firm clods and easily breakable, fine aggregates.
• Poor structure = Score 0 (right image): Soil dominated by extremely coarse, very firm clods with very few finer aggregates. Pulverizes into dust (too weak) or doesn’t break at all (too compacted).

What you will learn

• Good structure means good air and water flow for soil ecosystem and plant roots. Soil will hold water in dry weather, but will not become waterlogged in wet weather. It allows roots to explore a larger volume of soil, giving plants access to more nutrients and water.
• In contrast, a poor structure means loss of nutrients from run-off, erosion and drainage.

It indicates the stability of soil aggregates, resistance to erosion and, suggests how soil can maintain its structure to provide water and air for plants and soil organisms when it is rapidly wetted.

How to do it

1. Fill the jar(s) with water and hang a piece of a 1 mm mesh inside at the top of each jar (to prevent the soil sinking to the bottom directly).
2. Take an air-dried soil aggregate (4-6 cm diameter) from each zone (if you have conducted the drop and shatter test, select three pea-sized aggregates of soil from each soil zone).
3. Place different soil fragments in different meshes.
4. Observe soil fragment for 10 minutes and take a photo for record.
5. Give a score to your test after 10 minutes:
   Score 1= Complete slaking/poor condition (aggregate breaks down completely into grains)
   Score 2= Partial slaking/moderate condition (aggregate breaks but some remain intact on top)
   Score 3= No slaking/good condition (no change, water is clean)

What you will learn

• Healthy soil: aggregates hold together or gently crumble over time.
• Unhealthy soil: aggregates rapidly disintegrate and show signs of low organic matter.

What it is

Infiltration is the downward entry of water into the soil. Water from rainfall or irrigation must be able to enter the soil for it to be valuable. Soil temporarily stores water, making it available for root uptake, plant growth, and habitat for soil organisms.
The speed at which water enters the soil is the infiltration rate, which is typically expressed in millimeters or centimeters per hour.
Soil water infiltration tests measure how quickly water soaks into the soil, indicating soil compaction, porosity, and structure.

Why it matters

• Poor water infiltration will result in runoff, erosion, and poor root growth.
• Healthy water infiltration will result in better drought resistance and groundwater recharge.

How to do it

1. Select one or ideally two soil sample(s), next to the soil sampling you did for the 5 other tests but not in the same hole as the soil structure has been totally modified.
2. If the soil is too dry, soak the soil slowly for several hours with water before the test until saturated OR do the test 3 days after a substantial rainfall event with a clear forecast for the next three days.
3. Clear the vegetation from the sampling area.
4. Drive a metal tube half-way into the soil (e.g. if the tube is 12 cm high, you will have the tube 6 cm into the soil and the same 6 cm out).
5. Start the timer as you pour 500 ml water into the tube as gently as possible.
6. Stop time when all the water has infiltrated, when the surface is just glistening rather than submerged. If soil is uneven, count time until half of the surface is exposed and just shining.
7. Record time counts for each of the samples.

What you will learn

• If your infiltration rate is quick (5 minutes or less), it indicates your topsoil structure is good, with stable aggregates around which water can percolate down into the soil profile.
• If your infiltration rate is slow (15 minutes or more), it indicates your top soil structure is poor. The topsoil has unstable aggregates and is compact, blocking water from percolating downwards. Instead water runs off, taking topsoil and nutrients with it.
• In general, faster infiltration can suggest good crumb structure and aggregation, such as a healthy soil with high organic matter. Slower infiltration suggest the presence of compaction, reduced porosity (high traffic by machinery and/or livestock), and lower organic matter.

What it is

Soil pH is a soil chemical property which plays a key role in regulating nutrient availability and other soil processes. Nutrients are available for plant uptake at different soil pH, therefore different crops thrive at different pH values. 

Why it matters

pH values between 5.5 and 7.5 are suitable for most of the crops and animals because they can support a larger variety of nutrients.

Low pH = nutrient lockup, poor growth
High pH = micronutrient deficiencies

Knowing pH also helps determine if lime or sulfur is needed.

How to do it

1. Collect soil samples with a spoon, remove roots and vegetation debris, and place it in a container.
2.  Add the same volume of water as soil and stir the solution.
3. Dip the tip of the pH strip into the soil solution for 30 seconds, leave it for 5 minutes, and compare the resulting color with the scale shown on the color chart. The resultant color match will give an estimation of soil’s pH.

How to do it

Note: These options give a general idea, not exact numbers

• For alkalinity test: Add vinegar to a spoonful of soil. Fizzing = alkaline soil
• For acidity test: Add water to soil until muddy, then sprinkle baking soda. Fizzing = acidic soil

What you will learn

• Poor: pH values lower than 4 or higher than 8. Too acidic or too alkaline soil.
• Moderate: pH values 4- 5.5 or 7-8. Slightly acidic or alkaline soil.
• Good: pH ranging from 5.5 to 7. Neutral soil.

What it is

The presence and abundance of soil life can be estimated by a count of earthworms but can also including other soil organisms (e.g. insects, fungi and bacteria). Earthworms are natural tillers and indicators of a living, healthy soil ecosystem. 

Why it matters

Biodiversity supports nutrient cycling and pest control.
Earthworms improve structure, infiltration, and nutrient mixing.
Microbes break down organic matter and form humus.

How to do it

1. Dig out a 30x30x30 cm cube of soil. 
2. Count the earthworms you find as you break the soil apart.

What you will learn

• 0–5 worms: Soil may lack organic matter or be too compacted or dry
• 5–10 worms: Moderate biodiversity
• 10+ worms: Healthy, biologically active soil

What it is

Organic matter (OM) is the decomposed plant and animal material in the soil. It fuels soil life, holds nutrients, and improves water retention.

Why it matters

High organic matter content means fertile and resilient soil.
It supports microbial biodiversity and nutrient cycling.
It buffers against drought and erosion.

How to do it

1. Dig out soil
2. Look at the color from the soil sample you dug out.
   Soil color is often the most visually apparent property of soil. While color itself does not influence the behavior or practical use of soils, it does indicate important information about the soil’s organic matter content, mineralogy, moisture, and drainage.

What you will learn

Soil rich in organic matter is darker, richer, and more fertile.

• Dark brown to black color: high organic matter—great for plant growth.
• Light brown or gray color: low organic matter—consider adding compost or mulch.
• Red or yellow color: indicates mineral-rich soils (iron oxides) but not necessarily high fertility.
  Soil color is the indicator that shows how the organic matter and carbon content of soil changes over time, with particular landuse and/or restoration interventions.

Once you have completed your soil health testing, you will have a surprisingly clear picture of your soil’s:

• Texture (sand/silt/clay balance)
• Structure (crumbly vs. compacted)
• Hydrology (water infiltration)
• pH (acidity/alkalinity)
• Biodiversity (earthworms & soil life)
• Organic matter (color & stability)

Healthy soil usually has a loamy texture with a stable structure, darker color, neutral to slightly acidic pH (6–7), a good water infiltration, and plenty of earthworms.

If your results show issues, do not worry. Most problems can be improved with:

• Compost
• Mulch
• Cover crops
• Reduced tilling
• Regular organic matter additions

Healthy soil is the foundation for sustainable agriculture, climate resilience, and food security. Using these soil health testing indicators, anyone can get a surprisingly accurate idea of their soil’s health. You do not need fancy lab equipment or expensive tools to understand what’s happening beneath your feet.

Obtaining further information on soil properties requires the use of specialized equipment for tests in the field and in the laboratory as results are less likely to be influenced by user bias.
In the Soil Lab, we use additional equipment that also focuses on the 3 aspects of the soil.

• Microscope: measures abundance and diversity of microbiology in soil samples such as bacteria, fungi, and nematodes. (biological aspect)
• Kiln for the Loss-on-Ignition (LOI) Test: measures organic matter by burning a dried soil sample and weighing the difference. (biological aspect)
• Penetrometer: measures compaction and resistance to root growth. (physical aspect)
• Digital pH meter: gives precise pH values, more accurate than pH strips. (chemical aspect)
  *You can find more detailed information about our soil testing equipment here.

Involving our community

Soil health testing doesn’t have to be done alone. At the farm, we get volunteers involved through community and citizen science projects as well as school day programs.
Hands-on learning builds awareness and action from the ground up — quite literally!
As Soil Ambassadors in the Algarve for the citizen science ECHO project, we have been using these same 6 soil health tests for this European project which aims to map soil health across Europe!
Learn more about this project and how you can get a soil ECHO kit here.

🌱 The Soil Lab at Mud Valley Foundation is an onsite, field-based soil laboratory supporting research and education focused on improving soil health and agricultural production gains. Learn more about it.

👉 Learn more about our partner, Ecosystem Restoration Communities, whose ERC Soil Framework we use, by visiting their website.