Criteria for classifying soil texture

Soil minerals are composed of mineral particles of different sizes formed during weathering and soil formation. Soil particles of different sizes (ranging from 10 m to 10 m in diameter) have very different chemical compositions and physicochemical properties. Soil particles can be divided into several classes according to their size and their properties. Countries around the world usually have different criteria for the classification of soil grain size. The following figure shows the specific criteria for each soil particle size.

In the 1950s, China began to adopt the Soviet Union's Katschinski system, and in 1975, China formulated a corresponding classification standard, which was similar to the Katschinski system. In the late 1970s, China introduced the InternationalSociety of Soil Science (ISSS). In the 1990s, the United States system (USDA) was applied in China and gradually became the mainstream. All of the above four types of soil particle classification use five major categories, namely, stones, gravel, sand, powder and clay, but the classification standard of each category is different. In the international system and the American system, particles smaller than 2mm are regarded as soil; in the Kaczynski system, particles smaller than 1mm are regarded as soil. the FAO system and the American system have the same grading of sand, powder and clay particles.

There are 2 main grading of soil particles in China: 0.01mm as the boundary of the division, the particles with diameter of 1 - 0.01mm are called physical sand particles; and <0.01mm particles are called physical clay particles.

Several common grading mechanisms This standard was developed in 1995. ***8 levels:

2～1mm very coarse sand; 1～0.5mm coarse sand;

0.5～0.25mm medium sand; 0.25～0.10mm fine sand; 0.10～0.05mm very fine sand;

0.05～0.02mm coarse powder grains;

0.02～0.002mm fine powder grains; less than 0.002mm clay particles.

Soils with more than 1% of >2mm gravel in the composition of soil particles are designated as gravelly or gravelly soils, respectively, according to the gravel content.

Gravelly soil in the description of soil texture, in the texture name before the title of a certain establishment of texture, such as gravelly sandy soil, less gravelly sandy soil, etc.. Less gravelly soil gravel content of 1 to 5%; medium gravelly soil gravel content of 5 to 10%; more gravelly soil gravel content of 10 to 30%.

Gravelly soil. When the soil gravel content of more than 30% or more, according to the regulations, no longer record the name of the fine-grained portion, only indicate that it is a gravel soil. Its grading standards are: gravel content of 30 to 50% for light gravel soil; 50 to 70% for medium gravel soil; more than 70% for heavy gravel soil. Examination to the gravel in the folder fine-grained part of the material situation is different, in the production response is also very different, therefore, in the indoor test, the fine-grained part of the composition of the particles were measured, in the total texture is still named a gravel soil, but in parentheses is indicated in the fine-grained part of the texture of the name. Such as a soil & gt; 2mm gravel content of 65%, fine-grained part of the texture of loamy clay, the final name, it is designated as a gravelly soil (loamy clay) and so on. The texture classification criteria for the American system are shown at right.

The Kaczynski system is a two-tier classification, that is, according to the mass fraction of physical sand particles (> 0.01mm) and physical clay particles (< 0.01mm), the soil is divided into sandy soils, loamy soils, and clays three categories of nine classes, as shown in the table below. Kaczynski texture classification can be summarized in the following steps: according to the content of physical clay particles, the soil is divided into three major texture types of nine textures, determined by checking the table; according to the sand particles (sandy), coarse powdery grains (coarse powdery), medium and fine powdery grains (powdery), and the content of clay particles (clayey), the texture is further divided into textures, and determine the detailed name of the texture, the format of the second dominant grain class + the first dominant grain level + texture name"; according to the gravel content, a description of stony texture was added before the detailed name of the texture, with a gravel content of less than 0.5% as non-stony soil, 0.5% to 5% as light stony soil, 5% to 10% as medium stony soil, and more than 10% as heavy stony soil. The texture grouping of the Kaczynski system takes into account the different soil types, and there are different texture grouping criteria for steppe soils and red and yellow soils, grayed soil types and alkalized and strongly alkalized soils. The textural classification of soils formulated by China (1978) is based on the mass fraction of sandy, chalky and clayey particles in three classes of sandy, loamy and clayey soils in 11 grades, as shown in Table 3.2. According to the gravel content, when it is less than 1% it is non-gravelly (no title before the texture name), 1%-10% is less gravelly, and more than 10% is more gravelly.

Chinese Soil Texture Classification System

Combined with the characteristics of Chinese soils, the texture classification of Kaczynski of the former Soviet Union is mainly used in agricultural production. The soil texture classification drawn up by China (1978) is based on the mass fraction of sandy, powdery and clayey grains to divide sandy, loamy and clayey soils into three categories and 11 classes. A gravelly soil texture classification standard was developed for soils with a high gravel content. According to the gravel content, when it is less than 1% for non-gravelly (no title before the texture name), 1%-10% for less gravelly, more than 10% for more gravelly.