What Is Soil Structure?

Refers to the arrangement and combination of soil particles (including aggregates). In field identification, it usually refers to those structures of different shapes and sizes that can be separated from each other. The soil structure is formed by a combination of physical, chemical, and biological factors during the process of soil formation or utilization. It can be divided into three types: block, sheet, and column according to its shape; according to its size, development degree, and Stability, etc., are further divided into agglomerates, lumps, lumps, prisms, prisms, columns and flakes.

Texture analysis is mainly the analysis of the number and grade of individual soil particles in soil, the purpose is to understand the composition of soil particles, but it cannot reflect the existence of soil particles. Except for sandy soil, soil particles are aggregated under the condition of self-dividing to be expressed in the form of soil structure, and the effect of soil texture on soil production characteristics is often also expressed through soil structure. Soil particles are bonded to each other through different stacking methods to form a soil structure.

The soil structure is closely related to the soil texture. Soil textures that are too sandy or sticky are often poor. Soil texture is a very stable physical property of the soil, and the rate of change is very slow. Texture type), but the soil structure can be improved by artificial cultivation ^[1]

The term soil structure actually contains two meanings. One refers to the morphological characteristics of various structures; it refers to the "structurality" that regulates the physical properties of soil.

Soil structures are soil entities such as soil clumps, soil blocks, and soil pieces of different sizes, shapes, and properties that are aggregated with each other for different reasons. The soil structure is actually a soil aggregate formed by the accumulation and recombination of soil particles in different arrangements. Different arrangements often form different structures. The existence of these different forms of structures in the soil affects the soil properties, their mutual arrangement, and the corresponding pore conditions, which in turn affects soil fertility and cultivability. ^[1]

Soil structure

The horizontal axis is much larger than the vertical axis and it is called a sheet structure. In paddy soil with a long cultivation history and dry land soil with constant depth of long-term cultivation, due to long-term cultivation pressure, the soil particles are condensed into solid and compact thin pieces of soil and arranged in layers. The soil at the bottom of the plow tends to be sheet-like. The bottom layer of dry land plough is too thick, which is not good for crop growth, and affects the root, upper and lower layers of water, gas, and heat exchange, and the use of lower nutrients by the crops. It is necessary to have a plow bottom layer with a certain water permeability in the soil for planting rice, which can reduce the water leakage and support water and maintain fertilizer. The method of deepening the plow layer can be taken year by year to eliminate the dry land plow bottom.

Soil crusting and compaction often occur on dry land surfaces. Soil crusts can generally be divided into two types: physical crusts and biological crusts. The former is a surface layered hard shell formed by the compaction of fine soil particles under the influence of moisture, salt and other factors. Physical soil crust has a significant effect on soil water movement. Soil biological crust is caused by soil surface in desert and semi-desert regions A layered structure of biological soil surface formed by the growth of moss, lichen, ground money, fungi, bacteria, etc. Biological crusts generally occur in desert areas in arid and semi-arid areas. Therefore, biological crusts in desert areas are also called desert biological crusts, and they mostly appear on fixed sandy land, which is an important indicator of sandy land fixation.

Crusts often appear on sandy loam to light loam texture soils, which are generally thin (1 to 2 mm). Once the surface layer is dehydrated, it will dry and crack into fragments and the edges will rise upward. Compaction occurs mostly in the soil above middle soil. It is the deepening and continuation of the crust. It is generally 3 to 5 mm thick and also up to a few centimeters in thickness. After drying, it cracks into large mouths. It is plowed into large soil blocks. , Atmospheric pressure damages the seedlings, tearing the root system, causing a leaky run. Soil crusting can significantly reduce the rate of soil infiltration and increase surface runoff, which is not conducive to soil water retention. In addition, crusting also affects plant emergence, especially the emergence of dicotyledons such as cotton, which can lead to severe seedling deficiency.

Soil structure

The block structure is cubic. The three axes of length, width, and height are generally equal, the sides are generally not obvious, the shape is irregular, and the structure is compact inside. Generally, those with an axial length of more than 5 cm are referred to as massive structures, those with an axial length of 3 to 5 cm are referred to as bulk crystals, and those with an axial length of 0.5 to 3 cm are referred to as fragmented structures.

What farmers commonly call "earthquake" are the massive structures that are common in the field. Block structures generally appear on the surface layer of soil with little organic matter and heavy texture, and the subsoil and core soil layer are also common. There are many soils in the surface layer. Because they support each other, they form large voids, which accelerates the loss of soil moisture, leaks wind, and compresses the seedlings, preventing seedlings from unearthing smoothly.

Soil structure columnar structure

The columnar structure refers to a vertical structure whose vertical axis is greater than the horizontal axis. Those with insignificant edges and corners are called cylindrical structures, and those with obvious edges and corners are called prismatic structures. Most of them appear in the thick bottom soil layer, core soil layer and columnar alkaline soil alkalization layer. This structure has different sizes, is firm and firm, and the internal voids are dominant. The outer surface is often coated with iron-aluminum plastic film, the root system is difficult to extend, the ventilation is poor, and the microbial activity is weak. Large cracks often appear between structures, causing leakage of water and fertilizer. Elimination methods are often improved by gradually deepening the plow layer and applying a large amount of organic fertilizer.

Soil structure aggregate structure

Among the above-mentioned structures, the block-like, sheet-like, and column-like structures are all bad structures according to their properties and functions. The agglomerate structure is a good soil structure that meets the requirements of agricultural production.

The aggregate structure includes aggregates and microaggregates. Aggregate structure refers to the formation of small, spherical, loose and porous soil clusters under the influence of humus and other factors. The diameter is between 0.25 and 10mm, and the diameter is less than 0.25mm. The quantity and quality of aggregate structure reflect the level of soil fertility to a certain extent.

The characteristics of the pellet structure: it has a certain size and properties, with a diameter between 0.25 and 10mm, and is spherical; it has high stability; the pore thickness is reasonable, the internal small pores are many, and the large pores between the particles are many.

The micro-aggregate structure refers to soil aggregates with a diameter of less than 0.25 mm. In the paddy structure paddy field, the number of micro-aggregates is more important than the number of grains. The more fertile the paddy field, the larger the number of soil micro-aggregates. The measurement of soil micro-aggregates is helpful to understand the structure of soil micro-aggregates formed by native particles under water soaking performance. ^[1]