Topsoil can be divided into plough layer and plough bottom layer, also called humus leaching layer, which is the plough layer of mature soil; Forest-covered areas have litter layers. Topsoil, also known as topsoil, is a highly mature soil layer with the best fertility, farming and production performance; The lower topsoil includes the bottom of plough and the uppermost part of subsoil (also called semi-mature layer).
1, plough layer: the soil layer most affected by tillage, fertilization and irrigation, with a thickness of about 20 cm. The topsoil is easily affected by production activities, surface organisms and climatic conditions, and it is generally loose and porous, with frequent alternation of dry and wet, great temperature change, good permeability, rapid substance transformation and many available nutrients. Roots are mainly distributed in this layer, accounting for about 60% of the whole root system.
2. Plough bottom: It is located under the plow bottom and is about 6-8 cm thick. Typical plow bottom is very dense, with small porosity, less non-capillary pores (macropores) and more capillary pores (micropores), so it has poor air permeability and water permeability, and its structure is often flaky, even with obvious horizontal bedding. The pressure of farm animals and plows, as well as precipitation and irrigation, usually make it sticky.
The core soil layer is also called "raw soil layer". It is the middle layer of the soil profile. Located between topsoil and subsoil. Formed by substances filtered from the topsoil. Usually refers to the soil layer 50 cm below the topsoil. Because of the movement and deposition of materials, the surface soil and core soil can best reflect the characteristics of soil formation process. In cultivated soil, the structure of core soil layer is generally poor, with low nutrient content and few plant roots. The core soil layer of dry farming soil generally maintains the form and nature of natural soil deposition before reclamation and planting, and the change caused by tillage is small; In general, the core layer of paddy soil usually develops into a prismatic or prismatic striped layer.
The subsoil is located below the plow bottom, with a thickness of about 20-30cm. It can be compacted under certain plow pressure and livestock pressure, but it is not as good as the bottom of plow. In cultivated soil, subsoil is an important water and fertilizer conservation layer and the main water and fertilizer supply layer in the later growth stage. The number of roots in this layer accounts for about 20-30% of the whole root system.
The subsoil, also called parent material layer, is a layer in the soil that is not affected by farming and maintains the characteristics of parent material. If the soil-forming parent material is rock weathering debris, the subsoil is often mixed with these debris. The subsoil is below the subsoil, generally at a depth of 50-60 cm below the soil surface. This layer is less affected by the surface climate, but also relatively dense, with slow material transformation, less available nutrients and less root distribution. Generally, this layer of soil is called raw soil or dead soil.
When diagnosing whether a piece of land is healthy or not, or distinguishing the type of another piece of land from the type of this piece of land, we can see it with our eyes. These include: color, texture, cultivation, water capacity, drainage, depth and slope. I will discuss these attributes one by one, but you should know that they all affect each other.
The color of the soil can be seen whether it is healthy, whether it starts, and whether it will change after a long time. At the same time, it can also judge the color of its ancestors. From which soil did the patriarchal clan system develop? In my area, most of the ancestral soil is a mixture of stones. However, the raw materials of ancestors may be washed out by rivers, sand in desert areas or lava in volcanic areas. I often think that the soil also has ancestors like us.
The environmental quality standard of heavy metal soil formulated in 1995 in China can be used as a reference. The first-class standard stipulates that the lead content in soil is ≤35mg/kg, and the third-class standard should be ≤500mg/kg. Generally speaking, sandy soil has a low bearing capacity and is more susceptible to heavy metal pollution than cohesive soil.