Soil is a colossal natural we alth. It provides animals with feed, humans with food, and industry with the raw materials necessary for the production of goods. Soil creation has been going on for centuries and millennia. And today, humanity is faced with the question of the proper use of land. And this is impossible without knowledge about the structure, properties, composition and structure of soils.
History of the study of the fertile layer of the earth
Even in the 18th century, scientists noticed that the soil consists of various components. Interest in this property resumed much later. Thus, in Germany, from 1879 to 1899, studies in this field were published annually by Volney 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 herbaceous vegetation. These studies were of great importance. They proved that in agriculture the soil structureplays an important 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 practically not considered by scientists in the 50-60s of the last century. The reason for this was the criticism of the grass field system. Researchers began to question the role of soil structure in matters of fertility. And sometimes they denied it altogether.
However, some scientists continued to do research in this area. And here the works of Academician V. V. Medvedev are especially distinguished. The scientists studied the structure of the soil and its significance using micromorphological methods. At the same time, he used modern mathematical tools that make it possible to analyze and generalize the data obtained. The result of Medvedev's work was a monograph published in 2008 on the structure of soils. In this work, studies were summarized, which convincingly proved that the improvement of the thermal and air regime of the upper layers of the earth directly and indirectly affects plant growth.
Basic definition
What is soil structure? The definition of this term indicates that it is a collection of various aggregates (lumps) that differ in size and shape. Each of these elements consists of substances interconnected by plant roots, humus, etc.
The structure of the soil is of great importance. It is the main factor responsible for soil fertility. Especially important for humans is the structure of the soils of the upper horizon. This is the layer in which the development of the root system of plants occurs. A variety of soil organisms live in it. From this horizon comes 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.
Classification of soils by structure
The upper horizons of the earth may look different. They are unstructured and structural. The first of these types includes granulometric elements, the state of which is characterized as separate particle. A striking example of structureless soil is sandy. It contains little humus and clay particles. Transitional types of soil structure are between structureless and structural. In them, the connections of aggregates with each other are expressed very weakly.
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 allow it to be classified as fertile, then it has a balanced combination of air, thermal and water regimes. 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, rain runoff on such lands causes erosion. Air and water in such soils are antagonists. Falling rains do not leave moisture in such ground horizons. This happens due to the intense capillary rise of water. The soil is drying out. At the same time, plants are not provided with the amount of liquid and nutrients they need. Despite all this, in fields with structureless soils, it is possible to obtain a high yield. However, this will require constant work to keep agricultural technology at a high level.
Formation of the fertile layer structure
The upper horizon of the earth becomes suitable for plant life under the influence of two processes occurring simultaneously. Thus, the formation of the soil structure occurs as a result of the mechanical separation of the layer into aggregates of various shapes and sizes. The second process is to give internal properties and structure to the resulting elements.
Research by scientists has shown that the formation of soil structure becomes possible under the influence of chemical, physical-chemical, biological and physical-mechanical factors.
Thus, the formation of aggregates occurs when alternating drying and moistening, 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. Changes the properties of the top layer of the earth and various processing fields of the implement.
Also, the composition and structure of the soil depend on the presence of an adhesive. They are usually humic colloids. These elements, when coagulated, are capable of convertingsoil structure into water resistant. This characteristic depends on the amount of humus, the mechanical composition, the ability to retain and absorb water, and also to supply it to the surface through capillaries. After rain, a crust does not form on such lands, which reduces the access of oxygen to the roots of growing plants.
Heavy soils
According to their mechanical composition, fertile lands are divided into clay and loamy, sandy, and peat bogs. How are they defined? The mechanical composition of soils is examined by samples. Soil particles are taken from several places of the upper horizon, making indentations of 20 cm each. Next, the samples are mixed with each other and moistened to a pasty state with plain water. If you get a ball, but it is impossible to roll it into a cord, then the soil is classified as sandy loam. With easy implementation of such actions, the earth can be classified as loam. And in the case when a cord rolls out of the ball, which then closes into a ring, the soil is classified as clay. This type of topsoil is considered heavy. These soils have a high density and viscosity. They stick together easily and are difficult to process, thus confirming their name.
During digging, clay soil does not crumble. It forms large clods that are difficult to break and crush. If such land is plowed up and allowed to lie down for a while, 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 too small a structureaggregate particles, leaving only a small space between them.
High compaction of clay soils causes poor breathability. This, in turn, leads to the fact that the roots of plants are not sufficiently supplied with oxygen. The access of air to those microorganisms that live in such soils is also limited. A small amount of oxygen leads to a slowdown in the process of decomposition of organic substances to the final decomposition products. This makes the soil poor, unable to provide plants with the organic matter they need to grow. That is why there is scant biological life in the clay layers. Some parts of such lands are even called dead. They lack a developed microbiological environment.
Compression of aggregate soil particles is associated with such characteristics of land as their water permeability. A developed capillary system is not formed in clayey horizons. That is why moisture does not pass through them. The roots of plants in such fields can hardly get the much-needed water for their life.
Heavy soils have one more negative feature. If water accumulates in them, then it does not pass into the lower layers of the clay horizon. Significant volumes remain in the growth area of the root system of plants, which leads to its decay.
It is hardly possible to say that the best soil structure is clay. And this is confirmed by the flooding of the arable layer during rain. Falling drops break up small soil aggregates. clayeylumps pass into smaller components, partially soluble in water. The resulting slurry binds soil aggregates very tightly. After drying, such fields are covered with a hard and very dense crust, which limits the penetration of oxygen, moisture and light to the root systems of plants. This phenomenon is called "concrete soil". The action of sunlight leads to 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 poor biological life. This affects the impossibility of normal plant nutrition.
Low yields on such lands are a consequence of the fact that the clay layers, due to their density, are poorly heated by the rays of the sun. The most extreme areas for agriculture remain unheated throughout the summer period.
Heavy soil improvement
To obtain a normal crop from clay fields, the earth must 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 the regular introduction of loosening and lightening components into the soil. They canbe peat or sand, lime or ash. In addition, to create favorable conditions for plant growth, manure and compost will be required. These components will create a normal biological and nutrient environment in the soil.
Improvement of 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, dry quickly and become ready for further processing.
Light or sandy soils
For such horizons, a low proportion of clay particles is characteristic. The bulk of this soil is occupied by sand. Humus is found in them only in small quantities.
Sandy soils are called light for a reason. After all, it is quite easy to process them. And this is favored by the granular structure of the soil. Thanks to it, such horizons have high rates of water and air permeability. However, they are subject to erosion and are not able to retain moisture in their layers. In addition, sandy soils not only warm up well. They also cool down very quickly.
But this is not the only reason why it is impossible to say that the best soil structure is sandy. Biological life is poor in such horizons. This is due to a lack of nutrients and moisture for microorganisms living in such soils.
Sandy soil improvement
To obtain a good harvest, binding and compacting components are regularly applied to light soil. Improvement of soil structure,classified as light, becomes possible when mixed with peat or silt formations, drilling flour or clay. This will fill the pores between the sand particles. And for the emergence of a biological environment favorable for plants, the introduction of humus and compost will be required.
Features of sandy soils must also be taken into account in the issue of their enrichment with fertilizers. Light soils perfectly pass moisture through themselves, which washes out all useful elements from them. That is why mineral fertilizers in such fields use only fast-acting fertilizers and apply them often, but in small volumes.
Medium soils
Loamy lands are the most favorable for agriculture and gardening. They have the best soil structure, the differences of which lie in the granular clodiness. The composition of such a soil includes both solid, rather large particles, and fine dust-like 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 air permeability and water permeability. They perfectly retain moisture, and also quickly and evenly warm up under the influence of sunlight. Thanks to balanced moisture, a constant temperature regime is maintained in loams.
Improvement of medium soils
To supportthe supply of nutrients is at the proper level, loamy lands must be periodically fertilized with compost. Additional mineral and organic fertilizers are purposefully applied after a preliminary analysis of the condition of the arable land.
