Types of agrarian soils-Agriculture and the environment- (I)

The levels of deterioration to the environment caused by agriculture are a problem that we must tackle, since these damages are turning against our interests as producers and we are losing fertility in all types of agricultural soils.

The Agriculture

In this article we intend to deal with a very broad topic, such as Agriculture and for this task we will present the triad SOIL, WATER and CROPS and we will interrelate them with each other and also with the environment.

We start with THE FLOOR.

What are agricultural soils?

Agrarian soils are the result of the disintegration of the mother rock, by action of:

  • Physical agents:
    • Wind.
    • Water.
    • Temperature
  • Biological agents:
    • Microorganisms.
    • Plant roots.
  • And chemical agents:
    • The Oxigen.
    • Carbon dioxide

In this aforementioned disintegration, what happens is that the mother rock fractures and multiple fragments are formed and with the passage of time and the combined action of all the mentioned agents, these fragments separate into smaller particles.

Through the study of these particles and the present proportion, we know the properties of the soil.

The size of the soil particles is very important and they are classified according to this scale:

  1. Coarse sand between 2 and 0.2 mm in diameter.
  2. Fine sand between 0.2 and 0.02 mm in diameter.
  3. Silt between 0.02 and 0.002 mm in diameter.
  4. Clay less than 0.002 mm in diameter.
Tipos de suelos agrarios
Types of agricultural soils-samples

Composition in terms of the proportion of particles in agricultural soils

The composition in terms of the proportion of particles in agricultural soils acquires the following properties:

Agrarian soil texture

Soil components are a mixture of three basic elements: Clay, Silt and Sand.

Texture is the proportion of each of these components:

  • Facilitating your work.
  • Promoting water retention.
  • Allowing air circulation.
  • Assessing the speed with which the water can cross the ground.

In order to analyze the composition of the soil, a sample must be sieved and all elements larger than 2 mm must be removed. Thus we will have the three previous elements of clay, silt and sand in the different proportions that, according to the USDA ( United States Department of Agriculture) , give rise to the pyramid that classifies them.

Types of agricultural soils according to USDA- Importance of a good irrigation system
Types of agricultural soils according to USDA

As you can see, the classifications vary according to the percentage of silt, clay and sand.

Technique to find out the type of dry soil

There are many techniques to know what type of soil we have, and of course it can be taken to a laboratory to indicate its composition.

But to get an idea we can do a dry test with the only device of a sieve with 2-millimeter holes to remove coarse sand and other solid elements or take a handful of earth by hand and spread it. Depending on how crumbled it remains, we can assess whether it has a sandy tendency or, on the contrary, if it offers a lot of adherence, has a shortage of sand and is presented as silty or silty clayey.

Technique to assess the types of agricultural soils
Technique to assess the types of agricultural soils


Types of agricultural soils according to the water they retain

When we irrigate a crop, the best way to optimize water is drip irrigation > , then in the environment of the plant a wet bulb is generated that takes different forms depending on the type of soil.

Suelos agrarios-Tipos de terreno con bulbo húmedo y salinidad
Agrarian soils-1-Loam terrain. 2-Sandy ground. 3-Clay soil. 4-Sensors (probes) of humidity, temperature and conductivity at different depths. 5-Wet bulb. Few salts per washing .. 6-Slight accumulation of salts. 7-High accumulation of salts.

This influences the absorption of the root system. As the roots are shorter and need more water, the usually must be more clayey. However, if the roots are deeper and you don't need a lot of moisture, the soil should be more sandy.

Considering the water retention we can find soils:

  • Dry : if they are totally sandy, the soil is not very fertile because it does not retain water, it is considered to have a very light texture.
  • Puddled : clayey are considered heavy and compact and will retain a lot of water and nutrients.
  • Moist : the intermediate type that would be the franks , they retain water but without flooding. They are of medium texture and are the most suitable for most crops.

Other physical properties of agricultural soils


It refers to the order or placement of the constituent particles of the soil, sand, clay and silt . To understand the great importance of the soil being well structured, we must imagine a large pile of bricks stacked in no order and compare it with a large, well-built wall.

If we think of clays and organic matter such as concrete, in the pile of bricks we can only place the concrete without coherence, while on the wall it will be placed and distributed in its entirety.

A well structured soil has good agricultural conditions.


It refers to the gaps or pores that are formed between the constituent particles, and that are occupied by water or air.

The smaller the size of the constituent particle, the more pores there are. Hence the explanation that clay soils store more water than sandy soils.

Retention capacity

It refers to the volume of water that a soil is capable of retaining, the unit of millimeters of water per centimeter of depth is usually applied.

Here are two new concepts:

  • The field capacity : the highest water capacity capable of retaining a soil
  • The wilting point : the loss of this amount, so that the plants could no longer extract any amount for hydration.

The holding capacity is the difference between the field capacity and the wilting point.

THE Plantae MOISTURE SENSORS measure the retention capacity.

Irrigation scheme. 11-Humidity probe. 2-3-Conductivity probe. 4-Filtration of the subsoil. 5-Evaporation. 6-Perspiration. 7-Rain water. 8-Drip irrigation.


It consists of the ability of the soil to be crossed by water and air. And above all we are interested in knowing the speed with which the water descends through the profile. This speed is called infiltration speed and is measured in mm / hour. If irrigation or rainfall exceeds the rate of infiltration characteristic of the soil, the phenomenon of runoff occurs. There is a special type of runoff, known as drainage, and it is the phenomenon that produces the loss of water that the soil cannot retain towards deeper layers of the profile.

Soil atmosphere

It is of greater importance than is attributed to it by many farmers. As we can think, when the pores are not filled with water, they are filled by the air, but it is important that it is with a high oxygen content.

Regardless of the texture and structure, you have to know how many active roots we have, since they consume a lot of oxygen. When these roots dry, the aeration of the soil in which they were present is promoted. This is the basis for no-tillage or groundcover techniques.


This concept is global and measures all soluble salts, we have to take into account that the crop needs salts for its nutrition, but if the concentration is too high they become harmful.

This causes a soil to be called salinized when it has an excess of soluble salts, if the salts present are from the sulfate group, the soil is called alkaline , and if they are from the group of chlorides the soil is saline . If the salts of both groups are very high, the soil can become sodium-saline .

The unit of measurement for salinity is DeciSiemens per meter , or a multiple thereof.

The salts compete with the plants for the absorption of the water, since the roots can absorb water thanks to the osmotic pressure.

A salinized soil has a high osmotic pressure, this causes a decrease in its productive capacity.

We have to avoid salinization of our soil, this is the worst thing that can happen to it.

Usually we refer to soil as the topsoil or plowed depth, although in reality it is deeper, and it is very convenient to know all the available profile to be able to make good decisions about the management and which crops are the most suitable.

Sandy loam soil for pistachio
Sandy loam soil for pistachio

The crops and the soil atmosphere or

The atmosphere in the soil is of the utmost importance for oxidation processes. Tillage and plant covers are essential. The soil is the support of the plants and the store of water, air and nutrients.

Keep reading

Riego controlado con sensores-sondas
Irrigation controlled with sensors-probes-almond plantation

Sources consulted:



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