What Is Soil Classification?

Soil classification refers to understanding the soil systematically according to the occurrence and development laws of the soil itself. By comparing the similarities and differences between the soils, it can distinguish and classify all kinds of objectively existing soils, and systematically arrange their classification positions. process. Soil classification can reflect the natural developmental relationship between different soil types, and at the same time can give appropriate names to the divided soil types. ^[1]

Soil classification is based on the differences in soil properties and quantities, and systematically divides soil types and their corresponding classification levels to develop a soil classification system. Soil classification is not only a clue for understanding and distinguishing soils at different levels of generalization, but also a basis for conducting soil surveys, land evaluations, land use planning, and exchange of research results on soil science and agricultural production practices, as well as transfer of local soil production management experience . ^[2]

Soil classification represents the development level of soil disciplines. With the demand and development of socio-economic, especially agricultural practices, the accumulation of soil knowledge and the improvement of the level of soil classification, soil classification has also continued to advance and develop. Since ancient times, the development of soil classification has roughly gone through three important stages: the simple soil classification stage in ancient times; the modern soil epigenetic classification stage; the quantitative soil system classification (or diagnostic classification) stage. ^[4]

(1) Genetic principles

The theoretical basis of soil classification is the theory of soil genesis. Soil is an object that changes under the influence of five major soil-forming factors (parent material, biology, climate, terrain, time) and human factors. The so-called changing object refers to its continuous evolution and development, including the evolution of the space and time categories. The occurrence, development, and evolution of soil can be highly summarized in one sentence: soil is unified with its environment. The principle of soil genesis is the basic principle of soil classification.

(2) Principle of unity

The soil is a whole, the cultivated soil is developed on the basis of natural soil, and it has a relationship of occurrence. It insists on the viewpoint of unified soil formation, and uses the principle of uniformity to formulate a unified classification system. Thanks to

Soil classification and survey are the basis for understanding the soil, the basis for conducting land evaluation, land use planning, soil improvement, and the promotion of agricultural technologies in accordance with local conditions, and also the important basis for improving the fertility of cultivated land and formulating fertilization for soil testing. Soil classification should accurately reflect the law of the occurrence, development, and distribution of soil itself, as well as the characteristics or conditions of soil fertility. and so. Comprehensive consideration of soil formation conditions (natural and man-made), soil formation process and its attributes (including profile morphology and physical and chemical properties, etc.) as the basis for soil classification. ^[5]

The current soil classification system in China is established on the basis of learning from the Soviet soil classification system and combining with the specific characteristics of our soil. It belongs to the classification system of soil geology. During the establishment of China's current soil classification system, combined with China's second national soil census since 1978, it has been revised and improved many times. The current soil classification system in China adopts a seven-level classification system of soil classes, subclasses, soil classes, subclasses, soil genera, soil species, and subspecies. Among them, soil classes and soil species are used as basic classification units.

1. Tugang

The soil class is the highest unit of the soil classification system and is a generalization of soil types. Its division highlights the soil formation process, some common characteristics of the attributes, and the impact of major environmental factors on soil properties. For example, leached soil classes This type of soil is fully leached with lime, the soil is acidic and weakly acidic, and there are obvious leaching and sticking processes; it is characterized by the leaching and deposition of calcium in the soils of the calcareous soil class. Characteristics; The common feature of the saline-alkali soil class is the unique soil properties produced by the accumulation of soluble salts and sodium ions in the soil.

2. Subclass

The subclasses are divided in the same soil class according to the significant differences in soil properties formed by obvious differences in soil hydrothermal conditions. For example, in the semi-leached soil class, the dry red soil in the semi-humid and hot environment, the brown soil in the semi-humid and warm environment, the gray brown soil in the semi-humid temperature environment, and gray forest soil are common in the semi-leached soil category, but their attributes are obvious difference. For another example, the saline soil and alkaline earth subclasses of the saline-alkali soil class are qualitative differences between the accumulation of salt and the degree of sodiumification.

3 Soil

Soil is the basic taxonomy of advanced soil classification. It is divided according to the main soil formation conditions, soil formation process, and soil properties that result from it. The same soil should have some prominent and common occurrence attributes and Layer, so it should also have soil, chestnut calcareous soil, brown calcareous soil, although both have soil humus layer and calcium layer, but the thickness of the humus layer, the content of organic matter, the depth and thickness of the calcium layer, carbonic acid There are obvious differences in calcium content. The corresponding soil types are divided accordingly.

4 Subclass

The sub-category is a large difference within the scope of the reaction soil. It is divided according to the soil in different development stages or the type of transition between soils within the same soil range. The latter has an additional secondary soil formation process in addition to the main soil formation process. For example, the brown soil, brown soil, and leached brown soil in the brown soil are divided according to the different development stages of the brown soil. For another example, the albic black soil is a type of transition from black soil to albic soil. The soil genetic characteristics and improvement direction of the subtypes are more consistent than the soil types.

5. Genus

The soil genus is a middle-level taxonomic unit that transitions from a high-level taxonomic unit to a grass-roots taxonomic unit. It is divided according to some local factors that make the properties of soil subtypes different. Such as soil parent material and weathering crust types, hydrogeological conditions, small and medium terrain and human factors.

6. Soil

Soil type is the basic unit of grassroots classification in the soil classification system. The same soil species are located in the same or similar landscape parts, and their profile characteristics are basically the same in quantity. Therefore, the soil of the same soil type should occupy the same or similar small terrain parts, and the hydrothermal conditions are similar, with the same soil layer type, and the thickness, layer, and sequence of each soil layer are also consistent. Same or similar in nature. Because the same soil species has the same physical and chemical properties and biological habits, the suitable planting properties and limiting factors are the same, and they have the same production potential.

7. subspecies

Subspecies was called variety in the past. It is a subdivision within the range of soil species. It is a variation in some characteristics of soil species. It is generally divided by some changes in surface layer or cultivation layer, such as variability in tillability, nutrient content and texture. Mutation must have some relative stability. The division of subspecies plays an important role in guiding agricultural production.

China's current soil classification system is divided into 12 soil classes, 32 subclasses, 61 soil classes, and more than 200 subclasses.

The current soil classification system in China is based on the abundant summary materials of the second soil census, and the previous soil classification system is modified and improved. It is more reasonable than the previous soil classification system.

The current soil classification in China belongs to the genetic classification system. Another major soil classification system in the world today is the diagnostic soil classification system represented by the American soil system classification. The guiding ideology of soil system classification in the United States is a quantitative classification system based on the classification of soil properties. The theory of soil genetics is only used as a guide for selecting differentiating characteristics; a search table is used in the soil classification system, and exclusion methods are used to make strict boundaries between the taxonomic units; soil system classification is an open system that can accommodate any Taxonomic changes brought about by changes in soil knowledge without disrupting the entire system. So it can continuously improve the system based on new knowledge. Soil system classification has the characteristics of standardization, quantification, and internationalization, and represents the development trend of soil classification. ^[3]