Soil is a tremendous natural wealth. It provides animals with feed, humans - with products, and the industry - with the necessary raw materials for the production of goods. Soil creation continued for centuries and millennia. And today, humanity is faced with the question of the proper use of land. And this is impossible without knowledge of the structure, properties, composition and structure of soils.
History of the study of the fertile layer of the earth
Back in the 18th century, scientists noticed that the soil consists of various components. Interest in this property resumed much later. So, in Germany from 1879 to 1899, studies were published annually in this area by Wolni and his school. Numerous laboratory studies have established the dependence of the physical properties of soils on the size of its lumps and on the dust content.
In 1877, the scientist P. A. Kostachev noted that after plowing virgin lands they quickly disperse, which leads to a decrease in yield. The soil structure was restored only after the fields were left under perennial grassy vegetation. These studies were of great importance. They proved that in agriculture the soil structure plays a large agrotechnical role.
Much attention was paid to the study of the upper layer of the earth in the 30–40s of the last century. At the same time, scientists attached paramount importance to the structure of the soil in matters of fertility. They elevated these two terms to the rank of synonyms.
The structure of the soil and its significance were hardly considered by scientists in the 50-60s of the last century. The reason for this was criticism of the grass field system. Researchers have begun to question the role of soil structure in fertility issues. And sometimes they completely denied it.
However, some scientists continued to do research in this area. And here the work of Academician V.V. Medvedev is especially distinguished. Scientists studied the structure of the soil and its importance using micromorphological methods. At the same time, they used modern mathematical apparatuses that made it possible to analyze and generalize the obtained data. The result of the work of Medvedev was published in 2008, a monograph on the structure of soils. In this work, the studies were summarized, which convincingly proved that improving the thermal and air regime of the upper layers of the earth directly and indirectly affects the growth of plants.
Basic definition
What is soil structure ? The definition of this term indicates that it is a combination of various aggregates (lumps), differing in size and shape. Each of these elements consists of substances interconnected by plant roots, humus, etc.
Soil structure is of great importance. It is the main factor responsible for the fertility of the land. Especially important for humans is the soil structure of the upper horizon. This is the layer in which the development of the root system of plants takes place. A variety of soil organisms live in it. From this horizon is the supply of nutrients and water necessary for plant growth. That is why the topsoil must have an optimal ratio between its liquid, solid and gaseous phases. This proportion looks like this - 25:50:25.
Structure classification of soils
The upper horizons of the earth can have a different look. They are structureless and structural. The first of these species includes granulometric elements, the state of which is characterized as single-particle. A striking example of a structureless soil is sandy. There is little humus and clay particles in it. Transitional types of soil structure are between structureless and structural. In them, the bonds of aggregates with each other are very weakly expressed.
Fertile soil is considered structural. It better resists wind and water erosion, and also crumbles easily when plowing. If the composition and structure of the soil allows us to attribute it to fertile, then the combination of air, heat and water regimes is balanced in it. This factor has a positive effect on plant nutrition and the development of biological processes.
Unstructured soils are not able to absorb water well. In addition, rainwater on such lands causes erosion. Air and water in such soils are antagonists. Rainfall does not leave moisture in such land horizons. This is due to the intense capillary rise of water. The soil is overdried. At the same time, plants are not provided with the amount of fluid and nutrients necessary for them. Despite all this, high yields are possible in fields with structureless soils. However, this will require constant work that maintains agricultural technology at a high level.
The formation of the structure of the fertile layer
The upper horizon of the earth becomes suitable for plant life under the influence of two processes occurring simultaneously. So, the formation of the soil structure occurs as a result of mechanical separation of the layer into aggregates having different shapes and sizes. The second process is to give the internal properties and structure to the resulting elements.
Researches of scientists have shown that the formation of the soil structure becomes possible under the influence of chemical, physico-chemical, biological and physico-mechanical factors.
So, the formation of aggregates occurs when alternating draining and moisturizing, freezing and thawing. The composition and structure of the soil change under the influence of the vital activity of burrowing animals, from the pressure exerted by the growing roots of plants. The properties of the upper layer of the earth and the various processing fields of the tool change.
Also, the composition and structure of the soil depend on the presence of an adhesive. They are usually humus colloids. During coagulation, these elements are able to transform the soil structure into water-resistant. This characteristic depends on the amount of humus, the mechanical composition, the ability to retain and absorb water, as well as supply it to the surface by capillaries. After rain, a crust does not form on such lands, which reduces the access of oxygen to the roots of growing plants.
Heavy soil
By their mechanical composition, fertile lands are divided into clay and loamy, sandy loam, as well as peat bogs. How are they determined? The mechanical composition of soils is examined by samples. Particles of soil are taken from several places of the upper horizon, making in it recesses of 20 cm. Next, the samples are mixed with each other and moistened to a pasty state with ordinary water. If you get a ball, but it cannot be rolled into a cord, then the soil is classified as sandy loam. With the easy implementation of such actions, the earth can be classified as loam. And in the case when a cord is rolled out of a ball, which then closes into a ring, the soil is classified as clay. This type of arable layer is considered difficult. These soils have a high density and viscosity. They stick together easily and are difficult to process, confirming their name.
During excavation, clay soil does not crumble. It forms large clods that are difficult to break and crush. If such land is plowed and let it lie down a little, then all the work will go down the drain. After a while, the clods will stick together again. The field will have to be plowed again.
What is the reason for this behavior of heavy soils? It is associated with a too small structure of aggregate particles, leaving only a small space between them.
High compaction of clay soils becomes the reason for their poor breathability. This, in turn, leads to the fact that the roots of plants are not adequately supplied with oxygen. Access to air is limited to those microorganisms that live in such soils. A small amount of oxygen slows down the decomposition of organic substances to the final decomposition products. This makes the soil poor, unable to supply the plants with organic substances necessary for their growth. That is why scarce biological life is observed in clay layers. Some sections of such lands are even called dead. They lack a developed microbiological environment.
The compaction of aggregate particles of soil is associated with such a characteristic of lands as their water permeability. In clay horizons, a developed capillary system does not form. That is why moisture passes through them poorly. The roots of plants in such fields with great difficulty can get much needed water for their life.
Heavy soils have another negative trait. If water accumulates in them, then it does not pass into the lower layers of the clay horizon. Significant volumes remain in the area of growth of the root system of plants, which leads to its decay.
It can hardly be said that the best soil structure is clay. And this is confirmed by the swimming of the arable layer during the rain. Falling drops break small soil aggregates. Clay lumps turn into smaller components, partially soluble in water. The resulting slurry binds the soil aggregates very tightly. After drying, such fields are covered with a hard and very dense crust, restricting the penetration of oxygen, moisture and light to the root systems of plants. This phenomenon is called "concrete soil." The action of sunlight causes cracking of the soil, the structure of which for this reason becomes even more dense.
Yes, clay soils are rich in trace elements and minerals. However, plants are not able to take full advantage of them. The fact is that the root system can absorb only those nutrients that are in dissolved form, and are also the final product of the processing of microorganisms. Clay soils have poor water permeability. They have a poor biological life. This affects the impossibility of normal plant nutrition.
Low yields on such lands are due to the fact that clay layers, due to their density, are poorly heated by the sun. The most extreme areas for agriculture remain unheated throughout the summer period.
Improving heavy soils
To obtain a normal crop from clay fields, the earth needs to be given a looser and lumpy structure. Only in this case will favorable conditions for plant growth be created. How to improve the structure of the soil, which is considered heavy? This is possible with regular application of loosening and lightening components into the soil. They can be peat or sand, lime or ash. In addition, to create favorable conditions for plant growth, the introduction of manure and compost will be required. These components will create a normal biological and nutrient medium in the soil .
Improving the soil structure in terms of moisture capacity is possible when sand is added to it. This will simultaneously increase the thermal conductivity of heavy soil. After the sanding procedure, clay horizons warm up, quickly dry out and become ready for further processing.
Light or sandy soils
Such horizons are characterized by a low proportion of clay particles. The main volume of this soil is sand. Only in small quantities is humus found in them.
Sandy soils are not for nothing called light. After all, it’s not difficult to process them. And this is favored by the granular structure of the soil. Thanks to her, such horizons have high rates of water and air permeability. However, they are prone to erosion and are not able to retain moisture in their layers. In addition, sandy soils are not only well warmed up. They also cool very quickly.
But not only therefore, it cannot be said that the best soil structure is sandy. In such horizons, biological life is poor. This is due to a lack of nutrients and moisture for microorganisms living in such soils.
Sand Soil Improvement
To obtain a good crop, lightweight and compacting components are regularly added to light soil. Improving the structure of soil related to the lungs becomes possible by mixing it with peat or silt formations, drill flour or clay. This will fill the pores between the sand particles. And for the emergence of a favorable biological environment for plants, the introduction of humus and compost will be required.
Features of sandy soils must be taken into account in the issue of their enrichment with fertilizers. Light soils perfectly pass moisture through themselves, which flushes out all the useful elements from them. That is why mineral fertilizers in such fields are used only by high-speed ones and they are applied often, but in small volumes.
Medium soils
Loamy lands are most favorable for agriculture and horticulture. They have the best soil structure, the differences of which lie in the granular lumpiness. The composition of such soil includes solid, fairly large particles, and small dusty components. Land in such fields is quite easy to cultivate. After plowing, they do not cake and do not form dense lumps.
In loamy soils there are many minerals and nutrients, the supply of which is replenished due to the active life of microorganisms. Such soils have high breathability and water conductivity. They perfectly retain moisture, and also quickly and evenly warm up under the influence of sunlight. Due to the balanced moistening in loams, a constant temperature regime is maintained.
Improving medium soils
In order to maintain a proper nutrient supply, loamy lands need to be periodically fertilized with compost. Additional mineral and organic fertilizers are applied purposefully after a preliminary analysis of the state of the arable land.