The important role of soil colloids in soil fertility is described

Soil fertilizer retention and fertilization.

The so-called soil fertilizer retention and fertilization refers to the ability of soil to store nutrients and nutrients required by crops, which is an important characteristic that affects fertility.

a) Soil fertility retention.

In practice, it can be seen that after applying manure to cover the soil, the odor will disappear. Sewage can be cleared by passing through the soil layer. This shows that the soil has the ability to absorb certain substances. The ability of the soil to absorb fertilizer is called the fertility of the soil.

Soil fertilizer retention performance can reduce the disappearance of fertility, so that the fertilizer is stable and long, that is, it will not make the crops overfed due to more fertilization, causing crazy growth, and will not cause defertilization because of less or no application, so that the crops will starve.

Why does soil have fertilizer retention properties? The main reason is that the soil has soil colloidal substances, and soil colloids are the material basis of soil fertilizer retention properties. Soil colloids are due to very small particles (1 100 nm in diameter).

1 mm = 1000 nm), so the surface energy of this particle.

Larger, it will produce a strong attraction. In addition, the colloidal is charged and can adsorb opposite ions, so the more colloids in the soil, the more nutrients will be absorbed, and the better the fertilizer retention performance. Types of soil colloids: organic colloids - humus.

inorganic colloids - clay particles; Biocolloids—microorganisms. If we understand the principle of soil colloidal "fertilizer retention", it is not difficult to understand why sandy soil is weaker than clay soil, and lean fields are weaker than fertile fields.

2) Soil fertiliser.

The fertilizability of the soil refers to the ability of the soil to obtain nutrients from crops in a timely manner during the whole process of crop growth. Soil fertilization is reflected in the growth of seedlings, which is the problem of "early onset" and "late onset". Reflected in soil fertility, it is the large, small, front, back, stable, fierce, long, short and other problems of fertility.

The amount of available nutrients in the soil can reflect the quality of soil fertilization to a certain extent. However, potential nutrients and available nutrients are often transformed into each other under certain conditions. The so-called effective nutrients are water-soluble, substitutional and soluble ionic or small molecule nutrients that can be directly absorbed and utilized by crops in the current season; Potential nutrients are nutrients that cannot be directly absorbed and utilized by crops in the current season, and need to be transformed by microorganisms or other means, such as organic matter and mineral nutrients that are insoluble in water.

Factors influencing soil fertilization:

1. Soil structure: structured soil, unstructured soil;

2. Soil organic matter content;

3. Soil pH;

4. Soil temperature;

5. Soil moisture.

If the soil temperature is high, the soil moisture is suitable, and the minerals in the soil are weathered.

Fast, microbial activity is vigorous, and potential nutrients are released quickly. On the contrary, the soil temperature is low, there is too little or too much water, the microbial activity is weak, the release of nutrients (organic or inorganic) in the soil is slow, and the soil fertilizer supply is poor. Requirements in production:

Only "supplying" and not "protecting" is not good soil. Case in sandy soil. Only "protecting" and not "providing" is not good soil.

Case in green soil. Only land that is well "supplied" and "kept" is good land. For example, the soil has both small seedlings and old seedlings, and the crops grow steadily and strongly.

behave both.

Since the surface of the soil colloidal absorbs negative ions and becomes negatively charged, it can absorb positively charged ammonia ions, so that plants can utilize nitrogen.

1.The surface energy of the soil colloids is specific to the surface of the potato surface and the specific surface of the pants (the specific surface refers to the total surface area of the body per unit weight or unit volume).

2.Soil colloidal charge (divided into permanent charge and variable charge).

3.Soil colloids have agglutination and dispersion effects.

Its characteristics are celery: (1) its specific surface area is quite large (1g colloid is about 200 300m2), with considerable reactivity and adsorption; (2) Charged, with strong ion exchange; (3) It is the most active part of the soil and therefore has the greatest impact on soil properties.

Soil colloidal properties.

1. Specific surface and surface energy of soil colloids.

The surface of soil colloids can be divided into the following according to their location

Outer surface: The surface on which clay minerals, oxides such as Fe, Al, Si, and humus molecules are exposed.

Inner surface: Mainly refers to the surface between the layers of layered silicate mineral crystals and the surface inside the humus molecular aggregates.

Specific surface: the total surface area of the object per unit weight or unit volume, it is obvious that the smaller the particles, the larger the specific surface, as can be seen from Table 3-4 on page P72, the specific surface of sand and coarse powder particles is small and negligible compared to clay particles, so the specific surface of the soil actually depends mainly on the clay particles.

In addition, the surface of the soil particles is uneven, not a smooth sphere, its specific surface is larger than a smooth sphere, and most of the powder and clay particles are flaked and larger than the surface.

In addition, some inorganic colloids (such as montmorillonite clay minerals) have a huge outer surface, and the surface can expand between the grain layers, and there is also a huge inner surface.

In addition to the huge outer surface, organic colloids also have a huge inner surface. So organic colloids likewise have a huge specific surface. For example, humus molecules can be as high as 1000 g specific to the surface.

Since the soil colloids have a huge specific surface, they produce a huge amount of surface energy, and we know that the molecules inside the object are surrounded by the same molecules as it, so the molecular gravitational forces in all directions are equal and cancel each other out. Oak Nian.

The surface molecule is different, it is in contact with the external gas or liquid, and the internal and external sides are subject to different molecular gravity, which cannot cancel each other, so it has the remaining molecular gravity, and thus produces surface energy, which can do work and adsorb external molecules, the more colloids, the larger the specific surface, the greater the surface energy, and the stronger the adsorption capacity.

2. Charge of soil colloids.

According to the mechanism of soil colloidal charge, it can generally be divided into permanent charge and variable charge.

Soil colloids are divided into inorganic colloids (also known as sentolato mineral colloidal source chongbu, including montmorillonite, kaolinite, iron, manganese, silicon and other oxides and their hydrates), organic colloids (also known as humus colloids, ** in animals and plants, microbial residues and their decomposition and synthetic products), organic-inorganic composite colloids (formed by the close association of inorganic colloids and organic colloids through the gravitational attraction between ions and surface molecules, and such colloids are the majority in soil). Soil colloidal content affects soil water and fertilizer retention ability and tillageability.

For example, sandy soil with low colloidal content is easy to cultivate, but it is easy to leak water and fertilizer, which is not conducive to the growth of plants; The cohesive soil with high colloidal content has strong water and fertilizer retention ability, but poor air permeability, which is easy to lead to root and soil compaction. Only loam with moderate colloidal content has good tillage and good water, hail and ear fertilizer capacity, and is suitable for planting more crops. In actual production, vegetable farmers can improve the undesirable properties of cohesive soil and sandy soil by increasing organic fertilizer and soil deep ploughing.

Biotic Factors of Soil Formation Organisms are the most active factors in the process of soil formation due to soil organic matter. The production of fertility, which is an essential characteristic of soil, is closely related to the role of living organisms. The formation process from rock to soil under biological action is shown in Figure 9-7

Under suitable sunshine and humidity conditions, mosses are bred on the rock surface, which rely on trace rock minerals dissolved in rainwater to grow, and at the same time produce a large amount of secretions to chemically and biologically weatherize the rocks. With the proliferation of bryophytes, the interaction between organisms and rocks is increasingly strengthened, and soil is slowly formed on the surface of rocks. Since then, some higher plants have gradually developed on the young soil, forming a clear differentiation of the soil. Among the biological factors, plants play the most important role. Green plants selectively absorb nutrient elements from the parent material, water bodies, and the atmosphere, and make organic matter through photosynthesis, which is then returned to the surface in the form of litter and debris.

The differences in the amount and form of nutrient return of different vegetation types are the root causes of high and low soil organic matter content. For example, the organic matter content of forest soils is generally lower than that of grasslands, because grass roots are dense and concentrated in near-surface soils, and downward the concentration of roots decreases, thus providing a large amount of organic matter to the soil surface, while the roots of trees are deeply distributed and do not provide much organic matter directly to the soil surface, mainly in the form of leaf litter to return organic matter to the surface. In addition to providing organic matter to the soil in the form of excrement, secretions and debris, and promoting the transformation of organic debris through feeding and transport, some animals such as earthworms and termites can also change the soil structure, porosity and soil layer arrangement by agitating the soil.

Microbe.

1.Soil colloidal specific surface and specific surface energy (specific surface refers to the total surface area of an object per unit weight or unit volume).

2.Soil colloidal charge (divided into permanent charge and variable charge).

3. Soil colloids have agglutination and dispersion effects.