Soil analysis

It is necessary to understand ground soils in many cases. For example, to build, cultivate, make a pond or retention basin (without adding material), make bricks (raw or terracotta), make earth plaster, make pottery, separate elements from the ground soil to make natural filters or have another use of their biochemical properties…

Soil types

There are several types of soil, each with different properties which are able to support different species of plants.

The ground textures

Soil texture corresponds to the distribution in this soil of minerals and organic matter by size category, independently of the nature and composition of these minerals. [1]

The grain size itself relates to fine earth. [2]

• sands : > 50 µm
• silts : from 50 µm to 2 µm
• clays : < 2 µm

Sandy texture : well aerated soil, easy to work with, poor in water reserves, poor in nutrients, low anion and cation exchange capacity.
Silty Texture : Excess silt and insufficient clay can cause a massive structure to form, along with poor physical properties. This tendency is corrected by a sufficient content of humus and calcium.
Clay texture : soil chemically rich, but with poor physical properties ; impermeable and poorly ventilated environment, forming an obstacle to root penetration ; difficult tillage, due to high plasticity (wet state), or compactness (dry soil). A good structure favored by humification partly corrects these unfavorable properties.
Balanced texture : it corresponds to the optimum, insofar as it presents most of the qualities of the three preceding types, without having the defects. [3]

Sand is a granular solid material made up of small particles resulting from the disintegration of materials of mineral origin (essentially rocks) or organic (shells, coral skeletons, etc.) [4]

Silt is the ultimate product of fluvial erosion of rocks in the watershed of rivers. Silty particles are thus made up of very fine debris of quartz, mica and feldspar, or even clay minerals. [5]

Historically, in geology and soil science, the term clay corresponds to all minerals with a size of less than 2 µm in the rock. This grain size, invisible to the naked eye, is inherited from studies carried out by optical microscopy at the end of the 19th century. The crystals then having a size of less than 2 µm were not recognizable and classified under the name clay. [6]

In order to know the texture of your soil, you can perform the jar test.
For clay, the sausage test can be carried out.

The tests

Here, we will not detail tests, such as tasting the ground (which requires a lot of iteration before mastering with relative precision), nor the test of the buried underwear (in cotton, which shows the degradation after a certain time). Plenty more tests exist, we let you discover this for yourself, if you want to know more ! The ones shown here are sufficient to have a rather good knowledge about your soil, outside professional fields requiring precise data.
A test in a lab will show other things such as pollutants.

Touch

We take a little soil at 5-10 cm deep.
The soil must be dry (if not, set it aside and wait for it to dry).
We crumble the earth between our fingers. The grainier it is, the more sand it contains. The smoother it is (like wet flour), the more silt or clay it contains.
With experience, we end up having a certain precision in the touch test.

Jar test

• We take soil (about the equivalent of a large handful) at a depth of about 10-15 cm.
• We put it in a jar after breaking the large pieces.
• We add water to the jar approximately 3/4.
• We shake energetically.
• After 30 minutes, stir with a spoon. If there are pieces left, we shake so that everything is in suspension.
• We repeat the previous step as long as there are pieces left.
• Leave to settle for 24 to 48 hours.
• 3 phases are formed, sand at the bottom, silt in the middle and clay above.
• We measure the height of what has decanted and the height of each phase.
• We apply a cross-multiplication to know the percentages.

cross-multiplication principle.
The total height is 100%.
To know the percentages of each element, we do :
Phase height (sand, silt, or clay) / total height = percent of the phase

• The percentages are reported in the triangle below.
• Several measurements can be made to define an area in which the ground soil is located. If you do several tests, pay attention to the bio-indicators ! If on 5 square meters, the ground is different with lighter or darker grass, with plants that are found only on a limited area, then it can be very different. The reasons are multiple, a buried stump, an underground deposit of rubble, greater leaching, a different relief, pollution… Whatever the reason, this is not representative of the average ground soil.

Document

Source file

For people who master vector (svg made on Inkscape).

Sausage test

For the sausage test, a handful of soil is taken from about 10-15 cm deep.
It is compacted by moistening it with a little water. Then, we do the following steps in order.

Step 1
Form a 3 cm diameter ball and roll it in your hand.
Place it on a hard, flat surface. If the ball doesn’t hold together, the soil is sandy.

Step 2
Form a 10 cm long, 1 cm diameter sausage and roll it with your hand on a hard, flat surface.
If the sausage doesn’t hold together, the soil is sandy or sandy-loamy.
If the sausage holds together, the soil is at least 10% clay.

Step 3
Form a semicircle with the sausage.
If the sausage doesn’t hold together, the soil is made up of fine silt. If the sausage holds, it contains at least 15% clay.

Step 4
Form a complete circle with the sausage.
If the sausage doesn’t hold, it’s a fine clayey silt (10% to 28% clay).
If the sausage holds but cracks slightly, it’s a silty clay (about 30% to 40% clay).
If the sausage holds and is smooth, it contains at least 40% clay.

Step 5
If the sausage holds without cracking as in the previous step and can be twisted into a figure 8, it’s a heavy clay (50% to 100% clay).

Leaching test

Leaching is the loss of nutrients from the soil when it rains.
This can be done below (towards the water table, vertically or obliquely) or on the surface (lateral) in the case of very compact soil, such as clay. In the latter case, we speak of runoff.

• We cut a plastic bottle 10 cm from the top, to form a funnel.
• We make holes in the cap.
• Water is poured into the funnel.
• The cloudier the escaping water, the more leaching there is.
• If the water remains on the surface, runoff may occur.

Source file

For people who master vector (svg made on Inkscape).

Limestone and pH

Limestone forms aggregates (clay and humus form the clay-humic complex thanks to calcium and the work of earthworms) which retain nutrients and help raise the pH.

It’s all about quantity, you need enough, but not too much… See the « perfect soil » section.

• We gather soil taken from 10-15 cm deep.
• We put soil in a first glass (about a third).
• We add white vinegar or alcohol vinegar to wet the earth.
• The more foamy the result, the more basic the soil pH. There are several levels of reaction : You can hear effervescence at a minimum or have abundant foam at a maximum.
• We put earth in a second glass (about a third).
• We add water to make a mud while mixing.
• Add a teaspoon of sodium bicarbonate (or baking soda).
• The greater the foam, the more acidic the soil pH.

The red cabbage test is also pretty well known by chemistry teachers ! Cheap and with a good precision. (Here is an example, and another.)

Bio-indicators

The concept of bio-indicators was discussed in the part of the jar test.
If the ground soil has similar visual characteristics (Plants present and plants distribution…) then this defines two main things.

pH
Every plant grows with a certain pH. We can identify endemic plants (not the ones we planted, but those naturally present) via applications such as plantnet (https://plantnet.org/), via determination books, online forums from a photo, through more expert friends…
The ideal pH for plants is easily found on the internet.
For example, if we have a plant growing with a pH of 5.5 to 6.5 and another with a pH of 6.0 to 7.5 on the same area, then the pH is between 6.0 and 6.5, therefore slightly acidic.

Soil type
Likewise, every plant grows on a certain type of soil. We can identify them as mentioned previously and know if the soil is clayey, sandy, loamy, calcareous or humus.
We can also see if the soil is compact or airy, poor or rich in nutrients (and what kind)…
Databases on the type of plant matching the type of soil are easily found on the internet.

Organic material

• We take a little soil from about 5 cm deep (without roots or grass).
• We put hydrogen peroxide on the sample.
  • If a foam appears immediately and leaves quickly, the soil is rich in nitrogenous matter and poor in carbon.
  • If a foam appears late, the soil is rich in carbonaceous matter and poor in nitrogen.
  • If we observe a continuous, long and intense effervescence, the soil is balanced in carbon and nitrogen.

Humic clay complex

As said before, clay and humus form the clay-humus complex thanks to calcium and the work of earthworms.
This is the creation of aggregate in the soil to fix the positive ions that are not carried away by leaching.

Carbon and Nitrogen

The carbon and nitrogen elements are very important in the soil. The C/N ratio (carbon to nitrogen) largely determines the life of the soil.

Find more information here, with this exhibition (part « The chemistry of compost »)

The perfect soil

Land whose agronomic balance of the different elements that compose it would ensure regular growth of vegetation. Its theoretical composition is 65% sand, 15% clay, 10% humus and 10% limestone. [7]

Available water capacity

The available water capacity of a soil (AWC) is the quantity of water that the soil can absorb (soil water retention) and return to the plant. [8]
It is strongly related to soil type as we can see below in another texture triangle typology. (Source : Benitronne, CC BY SA license)
The higher the number, the higher the available water capacity.
It is also known as available water content (AWC), profile available water (PAW)[2] or total available water (TAW).

Document

Source file

For people who master vector (svg made on Inkscape).

Additional

For events, we created some additional documents.

Note

We added the following exhibition to our presentation :
https://www.graineahumus.org/soil-and-garden?lang=en

A sign with a global presentation

Source file

For people who master vector (svg made on Inkscape).

A sign presenting every experience

Source file

For people who master vector (svg made on Inkscape).

Ground texture triangle

We did the layout of the page of the ground texture triangle.

Source file

For people who master vector (svg made on Inkscape).

Relative size of ground textures

Source file

For people who master vector (svg made on Inkscape).

A Quiz

Question 1 : What is the clay-humus complex ?
A- A lack of value of the soil
B-A structure keeping minerals in the soil
C-A structure composed of clay and humus
=> Answers B and C are correct

Question 2 : How many bacteria are there in a handful of compost ?
A-More than there are humans on Earth
B-Around 10 million
C-None in a clean compost
=> Answer A is correct

Question 3 : Sort the soil structures in ascending size order
A-Sand/Clay/Silt
B-Silt/Clay/Sand
C-Clay/Silt/Sand
=> Answer C is correct

Question 4 : Which species are useful to create a favorable compost ?
A-Earthworms
B-Woodlice
C-Fungi
=> Answers A, B and C are correct

Question 5 : What is the job of a compost expert ?
A-A compost guide
B-A compost operator
C-It does not exist
=> Answer B is correct

Action debriefs

Action sheets are created for the set-up. Following the implementation, debriefs are done to improve action.
We use methods described on the website https://www.graineahumus.org/tools?lang=en

This project is following a workshop on ground soil analysis. Therefore, it is better to consider this one before, but it is not necessary.

It is composed of both advice and free videos.

For the garden, we will take the following elements into account :

• knowledge of the soil ;
• provisions ;
• cultivation on a non-suitable soil for what we are looking for ;
• what is helping cultivation ;
• the development of biodiversity.

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Know your soil

In the previous workshop, we have tackled how to know your soil.

Knowing your soil enables :

• to put plants that suit your soil ;
• to see if moving towards a culture that needs a soil close to the existing one is possible ;
• to help the soil, in itself, to be more living.

To obtain your soil type, see the tests on the other page or the bio-indicator plants.

You can also find the pie crust test that we did not deal with during the workshop.

Pie crust test

Take a handful of moist soil to have a kneaded dough that will hold.
Roll a glass bottle on it, like the way you would use a rolling pin.
Depending on the thickness of the dough, we have :

1. A clayey soil if it is less than 3 mm thick.

• A silty soil if it is between 3 and 5 mm thick.
• A sandy soil if we cannot roll it without breaking it.

Soils are often a mix of all, but there can be a prevalence.

Soil type

There are three types of soil based on the structure.

Clayey soil : heavy, compact, crackles when it dries, heats up slowly.
Silty soil : soft to touch, powdery when it dries, rich in organic matter.
Sandy soil : light, the soil squeals when rubbed between two fingers, heats up quickly, does not hold water, poor in organic matter.

Depending on the pH, the soil can be acid or limestone.

Modification of the soil

Clayey soil : Bring compost (with earthworms), to develop the clay-humus complex and to aerate the soil. Create a drainage system to avoid still water. Do not add compost often, but do it in profusion.
limestone soil : Use green fertilizers to neutralize and structure the soil. (See green fertilizers further down).
Sandy soil : Spread a big amount of organic matter to feed the plants. Have plants that are suited for the soil and less water demanding.
Silty soil : Use the right green fertilizers to aerate the soil.

Provision

Compost

See on the website.

Green fertilizers

Green fertilizers (or green manures) are temporary ground cover plants, which are able to do many things :
• Fixing nitrogen (legume family) ;
• Fixing phosphorus (mustard and buckwheat) ;
• Fighting against invasive plants (brassica family, that also fix potassium and phosphorus from rocks) ;
• Ventilating the soil (grass family, among others) ;
• Neutralizing the pH ;
• Fighting against erosion and leaching ;
• Limiting water evaporation ;
• …

So we will use an appropriate fertiliser for one’s soil and to its needs !

You can find many websites that list the different types of fertilizers, such as :
https://en.wikipedia.org/wiki/Green_manure
https://www.rhs.org.uk/soil-composts-mulches/green-manures

Once they expire, we can leave the green fertilizers there to turn them into a mulch, or you can put them in the compost or bury them to provide nitrogen.

Mulch

In nature, a living soil is hardly ever empty.

To reduce evaporation, bring carbon or restore a soil, we can use mulch or straw-mulching.

Mulch consists of covering the soil (with wood shavings, grass…)

Straw mulching is a type of mulch with straw.

There is also the R.C.W. that is not suitable for every soil. It is better for well-drained soils that are dry during summer, rocky…
It cannot suit very moist soils or clayey soils or soils with too much acid [9]

For practical matters, we can use mulch between rows of culture to avoid sinking in the mud.
We can then place them on the rows at the end of harvest. Therefore, we feed carbon to the cultivations by placing the mulch on the laid rows of the cultivations we just harvested, which are rich in nitrogen.

Ground cover

We can use a permanent ground cover to reduce the loss of water, ventilate the soils, reduce leaching…

Cultivation on a non-suitable soil for what we are looking for

If the soil is not suited for what we want, instead of excavating and bringing tons of vegetable matter, we can also look for the following cultivation techniques :

• Cultivation on straw bale.
• Cultivation on mound bed.
• Cultivation in sheet.
• Plank of amended culture (compost, manure, green fertilizers…).

We can also combine (cultivation in sheet on straw bale).

We can also talk about more popular types of cultivation, like greenhouse crops.

However, hydroponics and other types of cultivation without soil should be avoided if you care about the ecosystem and the development of its richness.

Help a cultivation

Types of plants

We can also look at the varieties we put by natural selection of local seeds, exchanges with neighbors, the use of naturally picked seeds that demand less water and that are more resilient against illnesses.
We avoid hybrids (F1, F2…)

Seedlings and cuttings

To spread the seeds, we can also sow on a hot layer, do our cuttings or seedlings with what is suited…

Allelopathy

Allelopathy [10] is the set of biochemical interactions between two or more plants. Some interactions are positive, others negative.

This works for plants that are next to each other, but also crops that follow each other in rotations.

A known example is the one of the three sisters that combines maize, climbing beans and squash.

Diversity

Having a diversity of species in the garden is important to balance the ecosystem and avoid invasive species, illnesses… that would devastate everything.

Welcome biodiversity

The more a system is diverse, the more it is resilient !

Global presentation

Other free video (with English subtitles)

Additional

For events, we created some additional documents.

Note

We added the following exhibition to our presentation :
https://www.graineahumus.org/soil-and-garden?lang=en

Website resources

Some interesting documents to tackle :
Soil horizons
https://commons.wikimedia.org/wiki/File:Soil_Horizons.svg

Visual Evaluation of a soil structure :
https://www.graineahumus.org/cherish-your-planet-to-your-level#VESS

Elements to take into account to plan our garden :

• What can the place be used for (depending on the soil, sun, prevailing winds, present elements : trees, walls…)
• Take into account the slopes (think about swales, furrow irrigation, a pond…)
• Allelopathy, associated culture and plants preferences (in terms of proximity and rotation)
• Early, side or in between preparation for cultivations (green fertilizer, mulch, ground cover, sheet, mound bed…)
• Remember the temporality of plants
• Cover the ground (mulch or permanent ground cover)
• What places for wild animals’ life ? (beneficial organisms, small mammals…)
• Prepare a vegetal terracing (with different levels : moss, grass, tall grass, bush, shrub, hedge, tree…)
• …

Wikimedia Commons links

https://commons.wikimedia.org/wiki/File:Triangle_texture_soil.svg
https://commons.wikimedia.org/wiki/File:Triangle_soil_texture_Jamagne_1977_and_available_water_content_(AWC).svg