When we talk about the necessary conditions for a certain crop, we pay close attention to the climate. Whether or not it will withstand the cold of winter or, on the contrary, the excessive heat of summer. The soil is a factor that is left in the background and is equal to or more important than the weather conditions. When we talk about clay, sandy, loamy soils … we talk about soil texture .
WHAT MAKES UP THE SOIL TEXTURE
Just as other variables can involve concepts that are somewhat complicated to explain, texture is a very simple concept. A soil is composed of particles, whose size classification is divided mainly into three: Sands, silts and clays. The different proportions of each of these phases constitute the texture of a soil.
HOW IMPORTANT IS THE SOIL TEXTURE
Both in large-scale agriculture and in the soil of our garden, the texture has direct implications in a multitude of processes and this conditions the proper development of the crops.
- When working the soil , the texture will define the difficulty of work. Very heavy clay soils are very difficult to work with. In an orchard we will notice it more or less, but in large productions, the costs in working hours and machine fuel skyrocket if the soil is too heavy.
- The gaseous phase of the soil. The soil must contain an important part of oxygen retained between the particles that compose it. Soils with very small particles (clay), the gaseous phase is minimal, such small particles do not leave spaces between them where oxygen can be retained. Sandier soils will have a much higher gas phase.
- Soil water . The water retention capacity also depends on the particle size of the soil and therefore its texture.
These three factors listed, apart from depending on the size of particles, we must mention that they are also a consequence of the level of aggregates in the soil, which we will talk about in future posts.
HOW TO MEASURE THE TEXTURE OF OUR SOIL
There are several methods to measure the texture of a soil. The vast majority of them consist of “home” physical tests of interparticle cohesion to give us a rough idea without quantifying what percentage of each phase (sand, silt and clay) the sample has.
In any method of soil texture measurement, a pre-sieving is done with a 2 mm light . Particles larger than 2 mm are considered to be the coarse elements of a soil and are not considered in the texture.
Starting from a soil sample with a previous sieving with 2 mm light, it is moistened with a few drops of water until it forms a paste with a certain plasticity.
Next, on a smooth surface or one hand with the other, try to make a very fine cylinder or “churro” about 3 mm in diameter:
- If you cannot form said cylinder and the sample falls apart, this is clearly sandy soil .
- If you can make the cylinder, try making a ring. If you get it and the touch is soft and fine, we are facing a clay soil .
- If you make the cylinder but when making the ring, it breaks, we are facing a loamy-clay soil .
- If you make the cylinder and the ring, but the latter has a not very smooth texture, then the soil will be loamy .
As you can see, this is a quick way with a maximum classification of 4 textural classes. If we want to make a more precise measurement we will have to resort to laboratory instruments , not very complex, but it is not something that can be done in the field.
The measurement of the textural classes is measured with the Bouyoucos method, based on Stokes’s law that you can find by browsing the web without difficulty.
Once the percentages of each of the three particle phases have been calculated, the most widely used method is the classification of the textural triangle, from the United States Department of Agriculture (USDA).
It is an equilateral triangle in which the percentage of each of the phases (sand, silt, clay) is represented on each side with a scale of 10 to 10.
3 lines are drawn perpendicular to the 3 sides of the triangle and where they converge at a point we can establish the type of soil we have based on the percentages obtained.
Here we leave you the triangle.
There are more methods to determine the texture of a soil and in FAO we can find some of them with illustrations. Here we leave you the soil texture link .