Definition of soil as a separate natural body

Savin Igor' ORCID: 0000-0002-8739-5441 Doctor of Agriculture Academician of the Russian Academy of Sciences, Doctor of Agricultural Sciences, Chief Scientific Associate 119017, Russia, Moscow, lane. Pyzhevsky, 7, p. 2, of. 25 savigory@gmail.com Other publications by this author

Introduction. Soil science is a young science. The term "soil" itself has been actively used, apparently, only since the middle of the 19th century. Thus, in the course of geognosy, compiled in 1839 by Colonel of the Corps of Mining Engineers D. I. Sokolov, the soil is defined as "the underlying rock, which is in the form of a layer, also called a bed or sole" ^[1].

In the Explanatory Dictionary of the Living Great Russian Language by V. I. Dahl (1882), soil is defined as "the earth, the foundation (from to rest, to lie). The upper layer of the earth" ^[2].

In 1883, V. V. Dokuchaev first considered the soil as an independent natural body formed under the influence of soil formation factors: "a combination of causes (parent material, climate, relief, age and vegetation)." Soil "is a function (result) of the mother rock, climate, and organisms multiplied by time" ^[3]. V. V. Dokuchaev's dissertation "Russian chernozem" ^[4] made soils an independent object of research, and the defense of the dissertation (December 11 (23), 1883) became the "birth date" of a new scientific discipline - soil science. Thus, in 2023, soil science turned only 140 years old.

This is a short period of time for science, so the conceptual framework of soil science has not yet been fully formed ^[5]. Many terms and definitions have remained unchanged since the time of V. V. Dokuchaev. However, the changes that have taken place over these 140 years (the accumulation of new knowledge about soils, the emergence of fundamentally new methods and technologies) dictate the need to modernize both the conceptual apparatus of this science and its foundations.

To paraphrase Friedrich Engels ^[6], we can say that the fundamentals of soil science cannot be considered "doctrinally and dogmatically, as something that should be memorized and then it will be enough for all occasions." The theoretical foundations of soil science need to be clarified and modernized. Without this, it is impossible to overcome the underestimation of its importance and isolation from practice.

The object of soil science, as a natural science, should be a natural object that is clearly defined in a semantic sense. This will allow you to define it in space as well. The vagueness of the definition of the object leads to great confusion and misunderstanding of the object of study by both soil scientists and non-specialists.

In 2024, Alex B. McBratney and Alfred E. Hartemink ^[7] presented a fairly complete review of soil definitions based on an analysis of scientific publications in recent years ^[8-12]. Based on the analysis, the authors proposed two versions of the definition of soil - a shorter and a longer one. Both definitions essentially define soil as a layered material on the Earth's surface formed as a result of chemical and biological processes and the physical organization of minerals and organic matter that supports terrestrial ecosystems and humans. According to the authors, a single-sentence definition and a more detailed definition are necessary "to achieve general consensus, recognition, understanding and use" ^[7].

In Russian soil science, the term "soil" refers to a natural body formed as a result of the transformation of the surface layers of the lithosphere under the combined action of water, air and living organisms ^[13]. This definition, in fact, differs little from V. V. Dokuchaev's definition ^[3].

Following V. Vernadsky ^[14], modern Russian soil scientists agree on the definition of soil as a "biosignature body". It is understood as a body, which is a mixed structure of living and inert matter. According to V. Vernadsky, a biosignature occupies an intermediate position between living organisms (plants, animals and microorganisms), their waste products, decaying, and inert bodies in the form of rocks. This is a very vague definition, and it is impossible to understand what this body looks like and what it is. Everyone can imagine a living organism, it has a clear definition. The stone also has a clear definition. And what is meant by the "intermediate" position between them is still unknown. If a "biosimilar body" is understood only as a mixture of living organisms, their waste products, and rocks, then such a definition does not make much sense. Each of these well-defined natural bodies is studied by a separate science, and they cannot be the object of study and soil science.

The proposed definition. Based on the above, it follows that the object of studying soil science has yet to be defined and clearly separated from other natural bodies. From our point of view, the definition of soil should be formulated regardless of who will use it. It is hardly correct to have one definition for scientists and another for non-specialist soil scientists. If we consider the soil as a separate natural body, the same as a plant or animal, then this body should be clearly defined for everyone.: for soil scientists, ecologists, agronomists and the general public.

We propose the following definition for discussion:

Soil is a natural body formed as a result of the transformation of waste from organic life and related processes under the influence of external conditions.

The adoption of this definition has many implications for soil science as a whole and for its various branches.

Implications for understanding soil properties, functions, and processes

By the term "organic waste" we mean the waste products of living beings living in the soil, under or above its surface: their dead bodies, secretions in the process of vital activity. It is the waste of microorganisms, fungi, plants, animals and humans. Under the influence of weather conditions, humans, animals and plants, these organic residues turn into a special organic substance (most often humus). Depending on the characteristics of the waste itself, external conditions, time, characteristics of the starting materials and groundwater, humus of various compositions and properties is formed. In this case, the processes of destruction and transformation of the formed humus can occur in parallel. The transformation of organic residues into humus is accompanied by other processes. The chemicals released in this case affect the mineral part of the soil, transforming it as a result of leaching, movement of substances along the soil profile, accumulation and aggregation of substances in the form of new formations. Over time, all these processes create a system of soil layers (genetic horizons) with various properties and manifestations that make up the soil profile. In the process of isolation of genetic horizons, they themselves, by their presence, begin to influence more and more the processes occurring in soils. Thus, the soil is formed - a natural object with specific properties, a set of genetic horizons and processes occurring in them.

As a result, the soil cannot exist without organic life. On Earth, there should be soil on almost every surface, including underwater. If there was no organic life on the moon and planets, then there can be no soil there. On terrestrial planets, weathering crusts may well form, but not soils. Theoretically, life on other planets could be based on silicon rather than carbon. Many science fiction writers write about this (see, for example, ^[15]), but there is no evidence of the existence of such a life yet. And at this stage of the development of science, the question of astropedology belongs more to science fiction than to science.

Various processes also occur in the soil under the influence of external conditions, but they cannot be considered soil formation processes. These are the processes of rock transformation, which can also form layers with different properties, but all these processes are not the result of the transformation of organic waste and are not an integral part of the life cycle. This is the main difference between these processes. Thus, the meaning of soil formation is the transformation of organic waste into fertile matter as a basis for the maintenance and development of life.

In other words, soil formation is the process of cleansing the biosphere of organic waste and turning it into the basis for a new life. It follows that life on Earth could not have originated in the soil. The soil is secondary to the origin of life on Earth. And, accordingly, the soil will exist for some time on Earth and in the event of the disappearance of life on it. During this time, the transformation processes of organic substances will continue until they are completely processed. The soil is not eternal and disappears after the complete destruction of its genetic horizons. The above is true for all soil horizons, and not just for horizon A. After all, the rocks that we observe on the Earth's surface, for the most part, passed the stage of soil formation, then were redeposited, and sometimes metamorphosed ^[16]. And these processes can completely destroy all evidence of previous soil formation on Earth.

It should also be emphasized that the main actors in the process of transformation of organic waste in the soil are living organisms, such as microbes, or animals. They decompose organic residues, which leads to their transformation. However, this activity takes place against the background of external environmental conditions (meteorological, hydrological, anthropogenic, etc.) that regulate the soil biome and determine the effectiveness and results of transformation.

By analogy with living organisms, soils show their "vital activity", that is, they function. The functioning of soils is aimed at their adaptation to changes in the external environment, as well as to changes in the external environment itself. The main result of the functioning of the soil is the realization of its purpose and role in the biosphere: the purification of the biosphere from organic waste and their transformation into the basis for a new life.

The whole variety of functions of the soil ^[17] directly or indirectly affects human life. This allows us to consider individual soil functions or their combinations as services provided by the soil to humans. This anthropocentric view of soil functions is not the only one. Soils provide similar services not only to humans, but also to plants, animals, microorganisms, and the entire biosphere.

The soil, being the result of the transformation of organic waste under the influence of external conditions, is the main place of their transformation in the biosphere. It is in the soil that waste is converted into a nutrient for plants, and their toxicity is neutralized. Thus, the soil is a link in a single global cycle of life on Earth: in the process of soil formation, waste products are transformed into soil, which ensures the reproduction and existence of life through nutrition and plant growth (fertility) as the beginning of the main trophic chains on the planet. This is the leading function of soils in the biosphere.

The soil profile is formed as a result of soil-forming processes, of which there are several dozen ^[18]. At the same time, the soil profile is a polygenetic formation, the various properties of which could be formed as a result of different processes and at different times.

Soil formation began immediately after the first living (organic) creature settled in the soil, on its surface or inside, and released the first waste products into the soil, which triggered the process of transformation of the mineral part of the soil and the formation of organic deposits in one form or another. This is how the processes of soil formation arose. They can be divided into the following groups: A) primary; B) secondary; C) indirect. Primary processes are directly related to the transformation of organic waste, which enters the soil along with excrement and dead living matter. Secondary processes are associated with the effects of organic matter transformation products on the mineral skeleton of the soil, with the destruction of previously accumulated organic matter (secondary init processes) and with the processes of movement (migration, removal, accumulation) of these products along the soil profile (secondary remote processes). Indirect processes include soil formation processes that are not directly related to the transformation of organic waste, the specifics of which are indirectly determined by the heterogeneity of the soil profile formed by primary and secondary processes. All these processes are influenced by external factors (meteorological (precipitation, temperature regime...), incoming solar radiation, the influence of vegetation, animals, humans, microorganisms, terrain) and the specifics of the parent rocks. The direction and force of external factors are very dynamic. Therefore, the climax state of soils can be achieved only theoretically. In practice, the results of soil formation in the form of individual features or horizons may completely disappear from the soil profile, or they may partially remain in the form of buried horizons or relict neoplasms. Thus, most soils on Earth at any given time are polygenetic formations in which individual properties or horizons may be of different ages and genesis.

Humans are just as much a participant in soil formation as plants, animals, or microorganisms. Human activity is an additional source of organic waste for its transformation in the process of soil formation. Humans also affect the soil mechanically, disrupting its profile, and chemically, introducing fertilizers and other chemicals (such as ameliorants) and polluting it. From this point of view, landfills of human waste are the substrate on which the initial stages of soil formation take place. If we accept this definition and consider humans to be the same factor of soil formation as animals, plants and microbes, then the initial stages of decomposition of compost or decomposition of any organic matter can also be considered the beginning of soil formation, and landfills can be perceived as specific anthropogenic soils.

Soil properties are the basis for soil diagnostics, assessment of their quality, and applied soil science in general. At the same time, the general uncertainty of the concept of "soil" leads to the fact that soils are often attributed properties that are not inherent in them. In many cases, the assessment of soil quality (namely soils, not lands) is based not only on the properties of the soils themselves, but also on the properties of other natural objects. This is logical, because V. I. Vernadsky wrote that the soil as a natural object cannot be considered in isolation from the environment ^[14]. However, this loses the practical meaning of assessing soil quality, which significantly reduces its importance and blurs the very concept of "soil" in the eyes of non-specialists.

From the point of view of our proposed definition of "soil", the parent rocks are not soil. This is the initial substrate on which soil formation takes place. An indicator of soil development is the difference in properties between the parent rock and the overlying layers. The absence of a difference indicates the absence of soil.

The remains of plants and animals in the soil that are not affected by decomposition should be considered inclusions. Rags are not a soil horizon, but only a part of plants. Forest litter, steppe felt and oaks also cannot be considered as part of the soil. Animal carcasses and dead microorganisms on its surface and in the profile are not soil. They are only a source of organic matter entering the soil, but not the soil itself. Animals, microbes, and plants (roots) are also not soil. The soil is only their habitat. Their dead parts, corpses that have not yet decomposed, are inclusions in the soil. And only converted organic waste can be considered part of the soil.

The physical properties of the starting materials have a direct impact on the transformation of organic residues through the regulation of soil regimes and processes. At the same time, the physical properties of soils are strongly influenced by the presence of recycled organic matter and its properties. The physical and hydrological properties of soils largely determine fertility even in the absence of organic matter. Thus, fertility is not an exclusive property of soils. This function existed before the appearance of soils and preceded their formation.

On the other hand, the vast majority of surface sediments (soils, soil-forming rocks) on Earth are, to one degree or another, the product of former biospheres (i.e., ancient stages of soil formation) in which soil products (and, consequently, soils) were completely destroyed by geological processes.

The air and water in the soil should be considered as part of the atmosphere and hydrosphere, respectively, and not as part of the soil. Indeed, the air and water in humans and animals are not considered part of them.

The mineral part of the substrate, which is not subject to changes in the process of soil formation, also cannot be considered as part of the soil. It is one of the material foundations of soil formation, but it is not a soil.

The chemical composition of the soil is determined both by the properties of the soil itself and by external factors: the properties of soil-forming rocks, the surface layer of the atmosphere, the properties and regime of soil moisture, climate features, and the effects of humans, plants, animals, and microorganisms on the soil. It is very difficult, and at this stage of the development of science it is almost impossible, to determine the contribution to the chemical composition of only a soil sample (without taking into account external factors). All of the above factors combine to create the chemical appearance of the analyzed sample.

The soil cannot have biological characteristics. Plants, animals, and microorganisms that live in the soil are not part of it. The soil is just their habitat. In the process of vital activity, they affect the soil, change its properties and affect the processes of soil formation. Thus, by the nature of their interaction with the soil, they differ little from humans. The study of plants, animals, and microorganisms living in soils is the subject of relevant branches of biology (zoology, microbiology, ecology...). They are hardly the subject of soil science. But the peculiarities of changes in soils under their influence are undoubtedly the subject of soil science.

Soils, like other natural objects, should be classified and systematized. It is as a result of the classification of these objects that their diversity and specificity can be assessed. Given the polygenetic nature of soils and the temporal variability of soil formation factors, it is incorrect to classify soils according to modern soil formation factors. It is also not enough to take into account the genesis of soils in the classification. Thus, factorial and genetic classifications of soils are unlikely to reflect their actual diversity. Soil bodies can be classified using substantive approaches. However, it seems logical to add information about modern soil formation processes. This will give the classification predictive power and an understanding of the trends in the main soil body. That is, ideally, the basic classification of soils should be substantive and process-based. The purpose of the basic classification of soils is not to solve specific applied problems, but to systematize and classify soils as separate objects of nature.

The above are just some of the implications of using the proposed definition of soil for soil science. Others may be established, for example, in the field of soil classification, soil mapping, and soil quality assessment. However, the purpose of this report was to show that, in addition to the classical definitions of the object of soil science, there may be other, alternative, logical definitions. Their existence is due to the youth of soil science and the insufficient amount of factual knowledge accumulated during its existence. They allow us to look at the soil as a natural object from a different angle, which can be useful for determining promising ways of developing soil science in the near future and for increasing the importance of this science in society.

Conclusion. In conclusion, it should be emphasized that the proposed definition of soil does not contradict the approaches of the founder of soil science, V. V. Dokuchaev. This is just an attempt to define the soil more clearly as an independent natural body, so that anyone can understand how the soil differs from the weathering crust, substrate or rock. When the concept of "soil" includes everything (from the microbiome to rocks), it makes the soil too vague in understanding, functions, properties and evaluation. Trying to overcome this uncertainty is the main goal of our proposals. Moreover, for V. V. Dokuchaev, the soil was precisely biocentric. For him, it consisted of a humus horizon (A) and a horizon extending to the parent rock (not affected by soil formation) (horizon B). He did not even consider horizon C (the parent rock) to be soil ^[4]. Thus, our proposal does not contradict this point of view, but only concretizes and reinforces it from the point of view of modern soil science.