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questions :Study of soil profile in field
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[Visitor (112.21.*.*)]answers [Chinese ]Time :2021-02-21
The morphological features of soil profile include soil structure, color, texture and structure at all levels of occurrence, which are the main basis for identifying and dividing soil types in the wild. Therefore, learning to observe and correctly describe the characteristics of documented profiles is an important basic function of soil field survey.
(1) Observation and division of the occurrence level and configuration of the section
Soil occurrence level and its arrangement combination characteristics (or profile configurations) are the product of long-term and relatively stable soil-forming effects. Due to the differences in soil-forming conditions and soil-forming processes of various types of soil, the soil occurrence level and its profile are not the same. It is one of the important morphological features to identify and divide soil types. The level of soil occurrence that represents the soil formation conditions and soil formation processes of a certain soil or sub-class may be called the diagnostic soil layer of that type. For example, the graying layer and humus deposition layer under the condition of cold temperate conifer forest formation are the diagnostic layer of gray soil, the dark humus layer and calcium and decontamination layer formed by the humus and calcification process under the vegetation condition of temperate meadow grassland, and the diagnostic layer of grassland soil.
According to the basic plan of soil profile occurrence level, combined with the soil formation conditions of the observation points of the practice area profile, the comprehensive characteristics of each soil layer, etc. to divide the occurrence level, and mark it with symbols. For example: A for the humus layer; A0 or 0 for the dead deciduous layer or felt layer; H for the peat layer; E for the gonorrhea layer; B for the deposition layer; C for the maternal layer; D or R for the parent rock layer. The differences between the traits and causes of each soil layer can be further subdivided and represented by a small letter to the right of the capital letters, e.g. Layer A can be subdivided into: Ah (surface humus layer of natural soil);.E-layers can be subdivided into: Es or A2 (graying layer), Ea (white slurry layer or rinsing layer), B layer can be subdivided into: Bt (sticky layer), BCa (calcium layer), Bn (humus deposit layer), Bin or Box (iron, aluminum oxide-rich The layers can be subdivided into Ca .C (loose), Cca (carbonate-rich), Ccs (gypsum-rich), Cg (subliminal), Bfe (thin iron disc), Bg (submerged), Cc (strong submersion), Cx (tight, dense brittle disc layer), Cm (glued)...
After the soil layer division, the continuous reading is used, and the depth of each layer is taken from the surface to the lower amount by steel tape measure, in cm, and the depth of the amount is recorded in the section record table. Finally, the soil structure is drawn as a profile pattern sketch.
(2) Sexual observation and description records at all levels of occurrence
The items listed in the section record table are described and documented hierarchically.
A, soil color:
Soil color is an external reflection of soil material composition and internal properties, and is the most significant sign of soil occurrence level appearance and morphological characteristics. Many soil types are named after colors, such as black soil, red soil, brown soil, brown soil, purple soil, and so on.
Soil color can reflect the composition and content of soil to some extent. If the darker the soil, the greater the organic matter content of the soil, the lighter the color, the smaller the organic matter content. The type and content of soil minerals also affect soil color. When the soil contains iron oxide, it is red, when iron oxide is watery, the soil becomes yellow, and when iron oxide is more, it becomes green and gray. When lime, silica and soluble salts are high, the soil becomes white. In addition, when the soil contains more water, it will darken the soil. Therefore, when observing soil color, pay attention to soil moisture. When the earth color is recorded, it can reflect the color of the natural state. Because the soil is an uneven body, often mixed soil color, recorded when the main color in the back, secondary color in the front.If the soil is mainly brown, the secondary color is gray and can be remembered as gray - brown...
The color of the soil should be compared in bright light, but not in the sun. The soil sample should be a fresh and flat natural crack, not a flat surface with a knife. The color of the soil sample may be very different from the color outside the natural soil, the color of the wet soil and the color of the dry soil are not the same, should be determined separately, generally should describe the wet state of the soil color.
B, soil texture:
The soil texture is identified in the field, which is generally a simple method of visual hand measurement. Although this method is more extensive, but in the wild conditions is still more feasible. The appraiser can also achieve the basic purpose of identifying the texture category by practicing it for a long time.
The identification of soil texture should pay attention to the identification and description of the "fine soil" part. When identifying the texture, observe first and touch by hand to understand the texture tactileness under natural humidity. Then and a little water, wet test, and then according to the method of Table 3 to determine the texture, fill in the record form.
Gravel soil texture description, to be in front of the original texture name with gravel words, such as gravel sand, less gravel sand and so on. 1) Less gravel: gravel content 1-5%. 2) Medium gravel: gravel content 5-10%. Poly gravel: Gravel content 10-30%.
The soil with gravel content of more than 30% is gravel soil, and the texture name of the fine grain part is no longer recorded and is distinguished by light weight, such as light gravel: gravel content is 30-50%. Middle gravel: Gravel content 50-70%. Heavy gravel: Gravel content is greater than 70%.
Table 3 Field soil texture identification specifications
Sand and soil scattered, almost all sand particles, very rough not fine strips, also not balls, when the soil particles scattered in the hands. , mainly sand particles
Sand loam loose, sand grain advantage, there are a little powder grain, can become a soil ball, can not be broken into a strip (broken into different sizes of broken segments) sand grain-based, mixed with powder grain
Light soil slightly tight, fragile, different thickness of the powder, coarse more, rough, slightly malleable, can be coarse 3mm of small soil strip, but the level pick up fragile. Mainly powdered grains
The medium loam is tight, and the powder, which is different in weight and weight, can be crushed with force, which is slightly rough. Plastic, can be formed into 3mm of small soil strip, but bent into a small circle of 2-3cm cracks. Mainly powdered grains
Heavy loam more tightly, hands can not be crushed, the weight of different powders, more fine, slightly rough feeling. Plasticity is obvious, can be molded into 1-2mm small soil strip, can be bent into a diameter of 2cm small circle without cracks, flattening cracks. Mainly powder grains, mixed with sticky grains.
Clay is very tight, not easy to break fine and equal powder, has a slippery feeling. Plasticity, bondability are strong, into 1-2mm soil strip, bent into a small circle flattened without cracks. Mainly sticky particles

C, soil structure:
Under natural conditions, soil is lightly touched by hand or other soil-taking tools and naturally scattered into shapes, i.e. the structure of the soil. Common in the wild are: block, nucleo, prismatic, flaky, granules and so on.
Block structure - near cube, vertical and horizontal axis is roughly equal, the edge angle is not obvious, according to its size can be divided into large block structure (axis grows up to 5cm), block structure (axis length 3-5cm) and fragmented structure (axis length 0.5-3cm), this structure in the soil texture clay, lack of organic surface soil is common, especially when the soil is too wet or dry the most easy to form.
Nuclear structure - near cube type, the edge angle is obvious, the axis length of 0.5-1.5cm, in clay and lack of organic texture in the substrate layer appears more.
Column structure - column structure vertical axis is much larger than the horizontal axis in the soil is upright state, according to the degree of angular obvious is divided into two, the angle is not obviously called cylindrical structure, angular angle is obviously called prismatic structure, this kind of structure is often in the heart soil layer, the subsolin layer appears under the alternating action of dry and wet formation, alkaline soil and alkaline soil in the heart soil often have a column structure.
Flaky structure - the horizontal axis is much larger than the vertical axis, is flat and thin, common in the bottom of the old farmland plow. In addition, surface crusts and plate formations formed after rain or irrigation are also flaky structures.
The group structure - the group structure is similar to the spherical, loose and porous small reunion, its diameter is about 0.25-10mm, the particle size is less than 0.25mm called the cluster particles.
D, tightness:
It is an indicator of the physical characteristics of the soil. The tightness should be tested with a specific instrument. In the absence of an instrument, soil tightness can be determined using soil extraction tools (section knives, shovels, etc.). Its criteria can be summarized as follows:
Very tight - it is difficult to wedge into the soil with tools such as earth drills or shovels, and it is difficult to compress it with greater force.
Tight - earth drills or shovels are not easy to press into the soil, with greater force to wedge in, but not deep.
Slightly tighter - it is easier to wedge into the soil with a drill, shovel or cutter, but the wedge depth is still small.
Loose - soil drilling, cutting knife is easy to wedge into a large depth, easy to break, pressure soil shrink more significantly, wet is also loose state.
Extreme pine - a soil drill that can enter the soil on its own, such as the surface soil of sand.
E, pores:
When the soil profile describes the pores, the size, number and distribution characteristics of the pores must be carefully observed and evaluated.
Size grading criteria for soil pores:
1) Small pores: 1mm < diameter.
2) Medium pore: 1-2mm diameter.
3) Large pores: 2-3mm diameter.
The amount of soil pores, divided by the denseness of the pore spacing or the number of pores on the unit area, is generally divided into:
1) A small number of pores: the pore spacing is about 1.5-2cm, there are 1-50 /cm2 pores, or 2.5 cm2 area has 1-3 pores.
2) Medium porosity: pore spacing of about 1cm, 10cm2 area has 50-200 pores, or 2.5cm2 has 4-14 porosity.
3) Multi-volume pores: pore spacing of about 0.5cm, more than 200 pores in 10 cm2, or more than 14 pores in 2.5cm2.
Soil pore shapes are:
1) Sponge-like: 3-5mm in diameter. It is meshed.
2) Cave tube holes: 5-10mm in diameter, holes formed by animal activity or plant roots interspersed.
3) Honeycomb-like: aperture is greater than 10mm, the pores caused by animal activities such as insects, showing a mesh-like distribution.
When observing pores, cracks in the soil should also be described. A fissure is a crack between a structure whose size can be divided into:
1) Small cracks: crack width < 3mm, mostly seen in the smaller soil layer of the structure.
Cracks in the 2nd column: the cracks are 3-10mm wide and are mainly found in the soil layer of the column-shaped, prismatic structure.
3) Large cracks: crack width >10mm, most commonly found in the column-shaped, prismatic structure of the soil layer;
F, soil moisture:
Soil moisture is the degree of soil dryness and humidity. Through the observation of soil moisture, not only can we understand the moisture condition and moisture of soil, but also help to judge soil color, tightness, structure, physical mechanicality, etc.
In the field, humidity can be measured by speed measurement method, but usually only with the eyes and hands to observe and touch, the criteria can be divided into: dry, moist, moist, humid, wet five levels.
1) Dry: soil-like in the palm of your hand, do not feel cool, no moist feeling, pinch it scattered into the face, blowing dust up.
2) Run: soil sample in the hands have a cool feeling, but no wet print, blowing dust-free, hand pinch can not be a ball, water content of about 8-12%.
3) Wet: soil samples placed in the hands, there is a distinctly moist feeling, hands pinched into groups, thrown loose.
4) Wet: soil samples placed in the hands, there are obvious wet marks, can be pinched into groups, thrown not broken, hand pressure no water flow out, soil pores more than 50% filled with water.
5) Wet: soil moisture is oversaturated, hand pressure can squeeze out water.
G, plant roots:
The type, number and distribution of plant roots in soil layer play an important role in soil formation process and soil properties, so it is necessary to observe and describe plant roots in the morphological description of soil profiles.
The observation and description of plant root system should mainly be divided into the weight and content of the root system, and its criteria can be divided into:
Rough breakdown by plant root, etc.:
1) Very fine root: diameter less than 1mm, such as the root of the undergraduate plant.
2) Fine root: diameter 1-2mm, such as the root of the undergraduate plant.
3) Middle root: diameter 2-5mm, such as the fine root of the woody plant.
4) Coarse root: diameter is greater than 5mm, such as woody plant coarse root.
According to the content of plant roots, can be divided into three levels of description:
1) Less roots: there are a small number of roots in the soil layer, each square centimeter has 1-2 roots.
2) Medium root: there are more roots in the soil layer, each square centimeter has more than 5 roots.
3) Multi-measure root: the inner root of the soil layer is interwoven, each square centimeter root is more than 10. In addition, if a soil layer has no root system, it should also be recorded.
H, newborn:
The new body is not the original substance in the mother-forming mass, but refers to the material produced during the formation and development of the soil. The more common new organisms are lime nob, lime prosthetic mycelium, lime cream, salt cream, salt crystal, salt crust, ferromanganese hard drive, clay hard drive, etc.
The species, morphology and composition of the new body vary according to the soil formation process and environmental conditions.
When describing the new body, it is d'to indicate what kind of substance, the existence of morphology, quantity, distribution status and color and other characteristics.
I, Intruder:
Refers to the material that is different from the soil master and the material produced in the process of soil production because man-made activities are added to the soil by the outside world. Common intruders are brick fragments, ceramic tablets, ashes, carbon slag, cinders, scorched earth blocks, bones, shells, stone objects, etc.
To observe intruders, we must first identify the substances that human activities add to the soil, or the substances that are soil erosion and then carry the sediments. Due to its different sources, it can be explained that the soil formation and development process differences.
The observation and description of intrusives should not only find out what substance, quantity, individual size and distribution characteristics, but also explore its causes, so as to help to understand the process of soil-forming.
J, lime reaction:
In the field to observe the soil profile, should be measured with 1:5 of thin hydrochloric acid, according to the foam reaction after the addition of hydrochloric acid, to judge the amount of calcium carbonate content, generally divided into no, weak, medium and strong four. Recorded as """"""
K, pH:
In cross-sectional observation, the PH value of quick soil can not only help to understand the nature of soil, but also can be used as a reference for soil field naming.
The measurement method can be measured by speed measurement - by mixing indicator color, or by pH widely test paper speed measurement. That is, the soil solution is soaked with distilled water, the pH mixture indicator is added (or the leaching liquid is extracted with PH extensive test paper), and then the standard color color ratio is used to determine the size of its pH, so as to judge that the soil is acidic, slightly acidic, neutral, slightly alkaline, alkaline.

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