Soil particles are divided into ,,, from coarse to subdivided

Natural soil particles are large and small, and their composition and properties are important for soil water, fertilizer, gas, heat and various physical and chemical properties.

plays a huge role. The soil particles are divided into several levels according to the size of the diameter, which is called soil particle grade, and the proportion of soil sediment is called soil texture, and the soil particles with a diameter of less than millimeters are generally called mud; Soil particles with a diameter of 1 mm are called sand; Soil grains with a diameter greater than 1 mm are called gravel.

At present, there is no completely unified standard for the classification of soil mineral particles, although the current classification standards for several soil particles are different, but they are generally divided into gravel, sand, silt and clay.

The main characteristics of each particle size of soil particles:

1. Gravel: mostly rock fragments, mountainous soil and floodplains.

Common in soil. When the soil history is full of gravel content, the pores are too large, which is easy to leak, run fertilizer, wear and tear farm tools, and is difficult to cultivate.

This type of soil is not conducive to the operation of machines and agricultural tools, the cost of improvement is high, the fertilizer and water retention is almost non-existent, and the cost of fertilizer and water input will be very high.

2. Sand grains. Sand grains are also known as "hot soil", easy to heat up and cool down, the temperature difference between day and night is large, which is conducive to the growth of roots and the accumulation of sugar, suitable for planting cassava.

"Pioneer crops" such as sweet potatoes and peanuts, crops with short growth periods, crops that are drought tolerant and barren, root vegetables and rhizomes, and crops that require early maturity.

3. Powder: Powder contains more in loess, the permeability is not strong, the capillary performance is obvious, the plasticity, cohesiveness, the adhesion is small, the expansion and contraction is weak, the water and fertilizer retention is strong, and the silica is strong.

The content is 60% to 80%, and the nutrient content is more.

4. Clay: high content in clay soil. Poor permeability, strong capillary performance, strong plasticity, cohesiveness, adhesion, significant tension and shrinkage, strong water and fertility retention.

The silica content is 40% to 60%, and the nutrient content is rich. It has good water and fertilizer retention and rich nutrients, but poor air permeability.

First, the structure is different.

1. Coarse-grained soil structure: Because the size of the particles in the coarse-grained soil can vary greatly, the small particles fill the pores formed by the large particles, and the density of the graded coarse-grained soil is higher than that of the graded coarse-grained soil. On the other hand, irregular particles can reduce density and increase porosity.

2. Structure of fine-grained soil: The skeleton of fine-grained soil is mainly a collection of different shapes and sizes. The types of aggregates are mainly composed of agglomerates, stacks, flocculates and outer particles.

Second, the size is different.

1. Coarse-grained soil size: composed of coarse and fine particles of different sizes, the maximum particles can reach more than 1000 mm, the finest can be less than millimeters, the particle size varies from a wide range, and the characteristics of coarse and fine particles are very different.

2. Fine-grained soil size: the maximum particle size of the particles is not greater than, and the nominal maximum particle size is not greater than the soil, including various clayey soils, silty soils, sand and stone chips. Among them, the maximum particle size of the particles is less, and the particle content is less than 90% (such as various cohesive soils, silty soils, sandy soils, sand and stone chips with different plasticity indexes, etc.).

Third, the division rules are different.

1. Rules for the division of coarse-grained soil:

1) The "Soil Classification Standard" (GBJ 145-90) adopts the former criterion, the particle group greater than 60mm is giant particles, the particle group less than or equal to is fine particles, and the gravel group and sand particle group are coarse particles, and then the two particle groups are compared. Soil with gravel mass accounting for more than 50% of the total mass is called gravel soil; Soils with gravel mass less than or equal to 50% of the total mass are called sandy soils.

2) The Code for Geotechnical Investigation (GB 50021--94) adopts the latter criterion, such as boulders or blocks with a particle size greater than 200mm and accounting for more than 50% of the total weight.

2. Rules for the division of fine-grained soil:

1) Soil with a coarse-grained group less than 25% of the total weight is called fine-grained soil.

2) 25%-50% of the total weight of the coarse-grained group is called the coarse-grained group fine-grained soil.

3) Contains some organic matter (organic matter content 5% 0. 10%).

Press GB T50145-2007:

The particle size greater than 60mm (macrogranular group) mass greater than or equal to the total mass of 15 soil is called macrogranular soil, which is roughly equivalent to boulder and pebble soil in engineering;

The soil with a particle size between the particles (coarse-grained group) and the mass greater than or equal to the total mass of 50 is called coarse-grained soil, which is roughly equivalent to gravel and sand in engineering;

The particle size is not greater than the particle size (fine grain group) and the mass is greater than or equal to the total mass of 50 The soil is called fine-grained soil, which is roughly equivalent to clay and silt in engineering.

According to the different particle content in the soil, the soil is generally divided into three categories: sandy soil, clayey soil, and loam.

The properties of sandy soil: high sand content, coarse particles, fast water seepage, poor water retention performance, and good aeration performance.

The properties of clayey soil: low sand content, fine particles, slow water seepage, good water retention performance, poor aeration performance.

The nature of loam: general sand content, general particles, general water seepage rate, general water retention performance, general ventilation performance.

The higher sand content is called: sandy soil.

Sandy soils with a high content of sand grains are relatively high.

By observing the thickness of the particles, the state when dry, the state when wet, and the degree of adhesion

More than half of the eggs (crushed) stones have a particle size of more than 20 mm, and the particles are completely dispersed, with no change in the surface and no sense of adhesion. More than half of the particles with a particle size of more than 2 mm (the size of a small sorghum grain) are completely dispersed, and there is no change in the surface and no sense of adhesion.

Gravel sand has a particle size of more than 1 4 mm (the size of a small sorghum grain, the particles are completely dispersed, the surface does not change, and there is no sense of adhesion.

More than half of the coarse sand has a particle size of more than 5 mm (the size of fine millet) and the particles are completely dispersed, but there are individual cemented together. There is no change in the surface and no stickiness.

More than half of the medium sand has a particle size of more than millimeters, the particles are completely dispersed, partially cemented but scattered when touched, and there are occasional watermarks on the surface, and there is no sense of adhesion.

Most of the sand particles, coarse bean rice flour approximate (> mm), most of the particles are scattered, a small amount of glue, there are occasional watermarks (slurry) on the surface, and occasionally a slight sticky feeling. Most of the sand particles are similar to millet grains, the particles are scattered in a small amount, and most of the glue surface has a significant slurry turning phenomenon and a slight sense of adhesion.

Answer]: B It can be seen from the division diagram of the grain group that the division of the fine grain group and the coarse-grained group is 2mm, and the division of the coarse-grained group and the giant grain group is 60mm. Split rent.

Because most of the soil on the top of the mountain is gradually weathered by the rocks in the area due to weathering and water erosion, it is basically undisturbed, so the soil particles are coarse; Most of the soil in the plains is relatively delicate due to the slow precipitation of wind and water currents.

A variety of particles in the soil that vary in size and shape and in very different compositions and properties. Soil particles can be divided into two types: single grains (also known as primary particles) and compound grains (also known as secondary particles). Single-grain, double-grained and structural bodies constitute the solid part of the soil, and the size, shape and distribution of soil particles and intergranular pores have an important impact on the physical and chemical properties of soil.

The substance that makes up the solid phase of the soil. According to its ** and composition, it can be divided into mineral, organic lead and organic matter and inorganic compound groups. Generally speaking, the mineral part accounts for more than 95% of the solid phase weight of the soil, and some are as high as 99%.

Coarse-grained soils are classified as follows:

1. Coarse-grained soil refers to the soil with more particles than millimeters, which is roughly equivalent to sand. Gravel soil, sand and pebbles, residual slope gravel soil and weathered rock ballast are collectively referred to as coarse-grained soil.

2. It is composed of coarse and fine Qi Song particles of different sizes, the largest particles can reach more than 1000 mm, and the highest volume can be less than millimeters.

Coarse-grained soil and fine-grained soil are the two main types of particles in soil, and they have some structural differences. Here are their detailed answers:

1.Coarse-grained soil:

Coarse-grained soil refers to particles in the soil with a particle diameter greater than millimeters, mainly including sand and gravel.

The gap between coarse-grained soil particles is large, the permeability is good, and the water permeability is strong.

The particle structure of coarse-grained soil is loose, which is easily blown away by the wind and is prone to erosion.

Coarse-grained soil has poor water retention capacity, is easy to dry, and has a short water retention time.

Coarse-grained soil has a poor ability to nutrientize plants, and fertilizers need to be added to provide nutrients.

2.Fine-grained soil:

Fine-grained soil refers to particles in the soil with a particle diameter of less than millimeters, mainly including silty soil, silty soil and clay.

The gap between the fine-grained soil particles is small, the permeability is poor, and the water permeability is weak.

The particle structure of fine-grained soil is compact, the stability is good, and it is not easy to be blown away by the wind.

Fine-grained soil has a strong water-holding capacity, which can accommodate more water, and the water retention time is longer.

Fine-grained soil is rich in nutrients and organic matter, and has a good nutritional ability for plants.

Summary: The main structural difference between coarse-grained soil and fine-grained soil is the particle diameter and the size of the gap between the particles. Coarse-grained soil particles are larger, have good permeability, poor water retention capacity, and low nutrient capacity.

Fine-grained soil particles are small, poor permeability, strong water retention capacity, and high nutrient capacity. The choice of which soil to use depends on the specific planting needs and soil improvement requirements.

Soil particles are formed by sticking to each other in different ways of accumulation. In addition to sand, soil particles are aggregated together in the form of soil structure under natural conditions, and the influence of soil texture on soil production traits is also expressed through soil structure. The types of soil structure are flaky, lumpy, columnar, and small-grained.

In the surface layer of drylands, flakes of soil crusts and lamination often occur. Interestingly, in desert and semi-desert areas, the soil surface is formed by the growth of mosses, lichens, fungi, bacteria and other lower plants, also known as desert biological crusts, which is an important indicator of the fixed status of sandy land. Block-like structures and columnar structures have few internal pores and are dense and compact, all of which belong to poor structures.

Farmers call large clods of soil as kola, and as the saying goes, "crops are not only afraid of grass, but also afraid of kola's bite". The best soil structure in agricultural production is the aggregate structure, which is a small soil mass that is approximately spherical and porous, with a diameter of between, and the diameter is called micro-aggregate.

The aggregate structure is generally more in the cultivated layer, and the masses call it "ant eggs" and "rice grits". The number and deterioration of aggregate structure reflect the level of soil fertility to a certain extent. In paddy fields, the number of micro-aggregates is more important than the number of aggregates, and the more fertile the paddy field, the more micro-aggregates in the soil.