What is soil and why is it important to plants?

The soil is the environment in which the roots of plants develop, and therefore their characteristics and properties will largely depend on their health. And it is that on the planet we live there are many types of soil, some are spongy and very rich in nutrients, others are composed of pores or coarse grains that may have almost no nutritional value but have excellent permeability.

Therefore, it is crucial to know the soil well, because in this way we can grow healthier and stronger plants. So, let’s get started.

What is soil and what is its importance?

Soil is important for plants

If we start at the beginning, we have to say that soil is the surface layer of the Earth’s crust . The part that most animals, including humans, step on, and where the roots of plants grow. But also, in almost all its layers we will find insects (such as earthworms or ants) and microorganisms (bacteria, fungi , viruses) that inhabit it.

The importance lies in a truth that, although a priori is unpleasant, is what allows the cycle to continue: everything that is alive, one day perishes. And when it does, all the nutrients it contains are released into the soil . For example, when a tree falls to the ground, the fungi will feed on its bark, until after a few years (it may be decades) of that trunk there is nothing left but those fungi that fed on it, which will also die some day and nourish the soil. These, when it rains, may be available for the plants to take advantage of.

But in addition to life and death, there is much more to any soil: water, air, rocks . We cannot forget either the phenomena that sometimes occur (but luckily they are occasional) and that affect it directly, such as the impact of a meteorite or an asteroid. Other events are more frequent, especially in the Pacific, such as volcanic eruptions.

Any event of this type can alter the soil, and therefore also cause changes in the life of the flora and fauna that inhabit it . For example, a volcanic eruption can easily destroy a forest in a few hours, torrential rains, already intense, can devastate orchards and gardens if they do not have an outlet for water.

There are things we can not avoid. That is, although today, for example, we can calculate the path that a meteorite is going to follow, more or less when a volcano is going to erupt, or what are the areas at risk of flooding, human beings cannot really fight against it. nature. It has to adapt, like other living things.

Plants have been doing it since their inception, more than 300 million years ago, and they will continue to do so until the Sun “swallows” the Earth, in about 5 billion years, if they do not become extinct sooner, of course.

What is the composition of the soil?

To know more about the soil, you have to know that it is made up of different layers that should be known if we want to know more about the way of life of plants:

  • First layer of organic matter , basically mulch and leaves, branches, etc.
  • Soil surface , is rich in humus. Its color is darker than that of the previous layer.
  • The subsoil is lower, and has less humus, so its color is somewhat lighter. The roots of the plants grow up to here.
  • Bedrock , which is basically rock fragments lacking in nutrients.

In addition to the aforementioned: air and water . These occupy the space that remains between the pores, or if you want granites, of the ground. The smaller these pores are, the more compact it will be and therefore the more difficulties the plants will have, since on the one hand, if they remain dry for a long time, then it will cost them more to absorb the water; and on the other hand, if too many days remain wet or flooded, the roots will rot.

On the other hand, if those pores are large, it will be a very light soil that will not retain water for long. This is ideal for some plants, such as those that live in arid or semi-arid regions ( agaves , arboreal aloes , etc.), but not for forest or jungle plants ( anthurium , maples , etc.).

What types of soil are there?

Depending on the type of soil it can be more or less rich

The soil is not the same in all parts of the world. Luckily, there are notable differences between the one I have in my garden in the south of Mallorca, and the one you can have in the north of the Iberian Peninsula. Furthermore, within the same province, even within the same neighborhood, no two soils are the same .

To give you an idea, the one I have is clay, brown in color and vulnerable to erosion because it rains very little and the degree of insolation is high. But the one in the north of the island is darker, since it rains more, there are many more plants (there are the forests of the Sierra de Tramuntana, for example), and therefore there is more organic matter that when decomposing nourishes the earth .

Thus, soils are classified according to their structure :

  • Sandy soils : they are very permeable, and consequently, they have almost no nutrients since the water carries them away. They basically contain sand. 
  • Silty soils : these have mostly silt. They are characterized by having very fine sediments that have been carried by rivers or the wind. They are also compact, but not too compact, and dark brown in color.
  • Limestone soils : are those that contain a large amount of calcareous salts. They can be light brown or white depending on the frequency and intensity of rainfall. 
  • Clay soils : they are composed of brown or reddish-brown grains. They have a lot of clay, so when it rains a lot, puddles tend to form.
  • Stony soils : as the name suggests, they are soils formed by stones and rocks. They do not retain water, unless there is a hole, so few plants grow in them (compared to those that grow in other types of soil).
  • Black earth : known as humid soil. It is the best to grow as it contains a large amount of organic matter, absorbs water but also filters it, and allows good root growth.

And they can also be classified according to their pH , that is, according to their degree of acidity / alkalinity:

  • Acidic soils : they are those that have a pH lower than 7. Their color is usually reddish-brown, and although plants can find all the micronutrients they need, such as iron, manganese, or chlorine, they will not always get nitrogen, phosphorus, potassium or calcium, either because they cannot absorb them or because they are not found in that soil.
  • Neutral soils : are those with a pH between 7 and 7.5. They usually have all the nutrients that most plants need.
  • Basic soils : also called alkaline soils. They are those that have a pH greater than 7.5. The main drawback they have is the presence of a large amount of calcium carbonate, which can prevent the roots from obtaining the nutrients they need.

Therefore, a soil can be clayey and also neutral; or sandy and basic.

In addition, depending on the pH of the soil in which the plants grow, we distinguish:

  • Acidic plants , which are those that grow in lands with a pH lower than 6.5, such as Japanese maples, camellias or hydrangeas, among others. 
  • Neutrophilic plants , which are those that grow in neutral lands, such as Ficus, Citrus or Prunus.
  • Alkaline plants, which are those that, on the contrary, do so in soils whose pH is 7 or higher, such as Pinus halepensis , Rhamnus alaternus or Olea europaea .

But this does not mean that they can only grow in soils with that pH. In fact, many alkaline plants do well in neutral soils, and vice versa as well. The acidic ones are more delicate, since when planted in soils with a high pH they immediately show symptoms of chlorosis (yellowing of the leaves, leaving the veins greenish).

Depending on the chemical characteristics of the soil, there are:

  • Chalcophilic plants , which grow in lands with a high percentage of limestone.
  • Calcifuge plants that are the ones that we will find in lands with low calcium levels.
  • Gypsophilic plants , which live in soils dominated by gypsum.
  • Nitrophilic plants , which develop only in soils with high percentages of nitrogen and nitrates.
  • Siliciculous plants , typical of lands with a large amount of silica.
  • Halophilic plants , which grow in soils very rich in salts.
  • Metalophilic or metalophytic plants , which can grow in soils rich in heavy metals such as lead or nickel.

How to raise or lower the pH of a soil?

Focusing a little more on land use in agriculture and gardening, we are going to see how we can change the pH of the soil if we want to grow a certain type of plant. But, first of all, we have to know what the pH is, and for this we can use a digital pH meter. This is inserted into the earth and, automatically, it will not say what it is.

But it can also be done at home , as follows:

  1. The first thing is to take several soil samples from the area where the plants will be, but not from the surface, but from further inland. What you do is divide that area into squares or diagonal lines, and take samples from different points at a depth of 10 centimeters if you want to grow small plants (vegetables, vegetables, herbaceous ornamental flowers), and 40 centimeters if what you want is to have trees, shrubs and / or palm trees.
  2. Afterwards, the samples are each placed in a container and distilled water is added. The ratio has to be 1: 1, for example, 200 grams of earth mixed with 200 ml of distilled water. Then stir well until a paste forms.
  3. After 1-2 hours, a pH strip is inserted to find out which one you have. In case you are not convinced by the result, do not hesitate to take samples again.

What to do to raise the pH of the soil?

If the soil we have is acidic and we want it to be neutral, what we have to add is ground limestone . A good layer, about four inches thick, mixed well with the local soil. But it is important that you keep in mind that this alone is not enough.

You have to take samples from time to time to make sure that the pH does not drop again, and it is also advisable that when planting the soil that is extracted from the planting hole is mixed with commercial substrates with a high pH of 6.5 or higher.

How to lower the pH of the soil?

Lowering it is more difficult. Normally the regions where there is alkaline soil there is also a water that is used to irrigate whose pH is high, which is what happens in many parts of the Mediterranean for example. Therefore, there are a few tasks to do:

The first is related to the land. To lower its pH , add low pH substrates , such as peat moss or coconut fiber, several times a year and mix well. Also, when planting, a large hole will be made – 1 x 1 meter is the best – and it will be filled with acidic substrates.

On the other hand, you have to check the pH of the water used for irrigation , with pH strips or a meter. If it is higher than 6.5, it will have to be lowered by mixing it with the juice of a lemon or vinegar. The amount to pour will depend on how high the pH is, but to give you an idea: if it is 8, fill a 1.5 liter bottle of water and mix it with the juice of half a lemon. Mix, and if you see that it is still high, add more lemon juice.

Soil drainage

A soil can have poor or good drainage

Image – Flickr / Prefecture of the Province of Guayas

The drain is another issue that I would love to talk to you about. And is that many plants have a hard time when grown on compact land. But what exactly is drainage? It can be said that it is the ease that soil has to absorb and filter water.

For example, if after torrential rain the site is flooded with 60 centimeters of water, and puddles form that remain for several days, that land is very poorly drained; but if on the contrary, it lasts a few hours, then it would be good.

How to know if a soil has good drainage?

A quick and easy way to find out is by making a hole and filling it with water. If the drainage is good, we will see that the water begins to filter from the first moment we pour it in, and it also does so at a good pace.

How to improve the drainage of the land?

There are several ways to improve it :

  • Install a system of drainage pipes and pumps.
  • Make a well or channel. You can even put water collection tubes that direct it to it, and thus be able to have rainwater to irrigate when necessary.
  • When making the hole for planting, make it large, 1 x 1m, to add a thick layer (about 30-40cm) of volcanic clay or gravel, and then mix peat with a little perlite.

As you can see, the soil is very important for plants. Knowing the one we have will help us cultivate a beautiful garden and / or orchard.

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