What is the texture of the soil and how is it measured?
When we talk about the necessary conditions for a specific crop, we look closely at the climate. Whether or not it will withstand the cold of winter or, on the contrary, the excessive heat of summer. Soil is a factor that is left in the background and is equal or more important than climatic conditions. When we talk about clayey, sandy, frank soils … we talk about soil texture.
What makes up the texture of the soil
Just as other variables may involve somewhat complicated concepts to explain, the surface is a straightforward concept. Soil is composed of particles, whose classification by size 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 texture of the soil
Both in large scale agriculture and the land of our garden, the surface has direct implications in a multitude of processes and this conditions the significant development of the crops.
- At the time of working the soil, the texture will define the difficulty of work. Clayey and hefty soils are tough to work with. In an orchard, we will notice it more or less, but in the big productions, the costs in hours of work and fuel of machinery, shoot up if the soil is too heavy.
- The gaseous phase of the soil. The soil must contain an essential part of oxygen retained between the particles that compose it. Grounds of tiny particles (clayey), the gas phase is minimal, so small particles do not leave spaces between them where oxygen can be retained. Sandy soils will have a much higher gas phase.
- The soil water. The water retention capacity also depends on the size of the soil particles and therefore, on their 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 soil aggregates, of which we will speak in future entries.
How to measure the texture of our soil
To measure the surface of the earth, there are several methods. The vast majority of them consist of “home” physical tests of cohesion between particles to get a rough idea without quantifying what percentage of each phase (sand, silt and clay) the sample has.
In any method of measuring the texture of the soil, a pre-screening with 2 mm light is made. It is considered that particles of more than 2 mm are the numerous elements of a floor and are not considered in the texture.
Starting from a soil sample with a pre-sieving with 2 mm light, it is moistened with a few drops of water to form a paste with certain plasticity.
Next, on a smooth surface or one hand with the other, try to make a skinny cylinder or “churro” about 3 mm in diameter:
- If you can not make this cylinder and the sample is undone, clearly we are facing sandy soil.
- If you can make the cylinder, try making a ring. If you get it and the touch is soft and delicate, we are facing a clay soil.
- If you make the cylinder, but when making the ring, it breaks, we are facing a loam-clayey soil.
- If you make the cylinder and the ring, but the latter has a not very smooth texture, then the soil will be frank.
As you can see, this is a fast 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 complicated, but it is not something that can be done in the field.
The measurement of the textural classes is measured by the Bouyoucos method, based on the Stokes law that you can find by surfing the web without difficulty.
Once the percentages of each of the three particle phases have been calculated, the most popular method is the textural triangle classification of the US Department of Agriculture (USDA).
It is an equilateral triangle in which are represented on each of the sides, the percentage of each of the phases (sand, silt, clay) with a scale of 10 in 10.
Three lines are drawn perpendicular to the three 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.