The most complete soil knowledge

(A) soil and its traits
1. The concept of soil: Soviet soil scientist Williams pointed out: "The soil is a loose surface that grows green plants on Earth's land." This definition correctly expresses the basic functions and characteristics of the soil. The reason why the soil can grow green plants, because of its unique nature - fertility. The special nature of soil is the basis for distinguishing soil from anything else. Although soil fertility is related to soil material composition, it is mainly affected by soil properties.
2, the main characteristics of the soil
(1) soil texture: the proportion of soil and sand called soil texture. Soil particles smaller than 0.01 mm in diameter are called mud; soil particles with a diameter of 1-0.01 mm are called sand; and soil particles larger than 1 mm in diameter are called gravel. The soil is divided into sandy soil, clay soil and loamy soil according to different soil texture.
① Sand: This kind of soil contains more than 80% of sandy grains, large intergranular macropores, and soil bulk density of 1.4-1.7 g / cm3. Therefore, the temperature difference between day and night is large, and the permeability is good. The mineralization of organic matter Fast, easy to cultivate, but poor water retention and fertility, water easy to get together, fertility is generally low. Planting crops to increase the application of organic fertilizer and a small amount of ground chasing fertilizer several times.
② Clay: This kind of soil contains more than 60% of mud and the proportion of soil is 2.6-2.7 g / cm 3. Soil hardness, adhesion, cohesion and plasticity are strong, so poor adaptability. Soil water and fertility, potential fertility higher. However, soil tillage, soil temperature is low, fertilizer is not easy to play. Therefore, paddy fields should pay attention to water control, increase mud temperature, apply more maturity organic fertilizer and heat fertilizer.
Loam: This kind of soil has a moderate proportion of silt, which accounts for 40-55% of the total, and 45-60% of the stick (mud). Soil bulk density of 1.1-1.4 g / cm 3. Easy texture, breathable water, water and fertility, farming plow. Therefore, it is water, fertilizer, gas, heat and coordination of high-quality soil.
(2) soil structure: the formation of aggregates of soil properties, known as soil structure. Where soil particles cemented into a diameter of 1-10 mm granular granular soil structure, known as the aggregate structure. This is the best kind of soil structure. The formation of two conditions:
First, cementing material. Soil cement is the most important clay particles, the newly formed humus and microbial mycelium and secretions. Together with the calcium, these substances form a water-stable granular granular soil structure that is porous and nutrient-rich and resistant to blistering. Therefore, the application of calcareous fertilizers (lime, gypsum) favors the formation of aggregate structures.
Second, the role of external compression. Any crop root interspersed, alternating wet and dry, alternating freeze-thaw and farming are agglomeration of the soil particles have a certain external force squeeze, so that broken into a certain size of the pellet. Deep tillage, no tillage, drip irrigation, and rotation of water and soil all contributed to the formation of soil aggregate structure.

The specific performance of the pellet structure:
First, it can coordinate the contradiction between soil moisture and air. Due to the existence of large pores between the particles, there are capillary pores within the pellet, which is conducive to moisture, nutrients, air exist between the three. So that the soil water, fertilizer, gas and heat conditions coordinated.
Second, have a good nutritional status. With the solution of water and gas contradictory, but also solve the contradiction between moisture and nutrients. Because the surface of the pellet is often gas-sensitive decomposition, pellet internal and also for the gas decomposition, the former is conducive to soil nutrient release to the crop absorption, the latter is conducive to the accumulation of soil humus, nutrient preservation. The contradictory coordination of water and nutrients can supply crops simultaneously and continuously.
Third, make the soil soft and appropriate. The soil with pellet structure is loose and porous with low plowing resistance, tillage and labor saving, good quality of tilling, fine and uniform soil, not hard and not floating sludge, Also small.
(3) soil absorption. Soil has the ability to absorb solids, liquids and gases. Its absorption method is divided into five kinds.
① mechanical absorption: This refers to the soil will be suspended in the soil than the pores and the solution (such as bone meal, cake fertilizer, phosphate rock powder and fecal residue, etc.) of the fine particles mechanically blocked, so that no seepage with the soil and flow away A role. As the smaller the soil particles, arranged more closely, the finer the soil pores, so the stronger the mechanical absorption, the soil fertilizer performance like. This effect on the newly modified rice fields, new reservoirs, pond dam conducive to enhance the function of retaining water.
② Physical Absorption: It means that soil colloids rely on their surface energy to adsorb molecular nutrients on the surface, while colloids and adsorbed materials can not afford any chemical reaction. This role, due to the maintenance of molecular nutrients, therefore, soil ammonia, urea, amino acids and other molecular nitrogen will reduce the evaporation loss. This is the reason why complex soils are often required when applying volatile ammonium nitrogen fertilizers.
③ chemical absorption: This refers to the soluble nutrients in the soil (such as certain ions and charged with different ions in the chemical role), by the role of pure chemical insoluble precipitate formed and fixed in the soil. Although this effect can reduce the loss of soluble nutrients, the nutrients that are immobilized can hardly be absorbed and utilized by the crops, thus reducing the utilization rate of nutrients. Therefore, the concentration of phosphate fertilizer or fertilizer mixed with organic fertilizer, made of ball fertilizer and root spraying, is to avoid the occurrence of chemical absorption and reduce soil phosphate fixation.
④ Substitution Absorption: This is also known as physical and chemical absorption. It refers to the surface of soil colloids adsorbed with many ions with opposite charges at the same time, its surface has the equivalent charge of other ions are replaced out of the role. Its essence is a kind of ion (cation or anion) substitution process, the ions absorbed by the soil colloid and the ions in the soil solution are replacing each other. So this effect is reversible, that is absorbed by the colloid ions, but also to be replaced by other ions to the solution. Thus, this role is of great importance in regulating the storage and supply of soluble nutrients in the soil.
⑤ biological absorption: This refers to living in the soil of microorganisms and crop roots and animals, absorb nutrients constitute the body and retained in the soil in a performance. Because organisms are based on their own needs, from the soil solution to choose to absorb a variety of soluble nutrients, the formation of organisms. When they die, the organic debris is gradually decomposed, releasing nutrients for crop absorption and utilization. Therefore, the role of bio-absorption, can maintain nutrients, nutrients accumulation, improve soil fertility.
(4) soil pH. Soil pH refers to the amount of H + and OHˉ present in the soil solution. Usually PH value. When PH = 7 is a neutral reaction, then the number of H + and OH ˉ in the solution is equal; when pH is less than 7, it is an acidic reaction, then H + is more than OH ˉ; if H is more than 7, it is a basic reaction, then H + is less than OH ˉ. Soil pH according to the size of its PH value is divided into seven levels:
PH <4.5 strong acidity
PH 4.5-5.5 Acid
PH5.5-6.5 slightly acidic
PH6.5-7.5 Neutral or near neutral
PH7.5-8.5 slightly alkaline
PH8.5-9.5 Alkaline
PH> 9.5 strongly alkaline
① causes of soil acidity and alkalinity: the reason why the soil has acid-base, mainly soil acid-base substances. The H + source is mainly H + and Al + 3 adsorbed on soil colloids; the second is the dissolution of carbon dioxide in water to form carbonic acid:
H2CO3 = H ++ HCO3ˉ, HCO3ˉ = H ++ CO3ˉ
In addition, there are organic acids (butyric acid, oxalic acid, citric acid and the like) generated during decomposition of organic matter, acid formed by chemical changes (such as oxidation of sulfurous minerals) and the application of fertilizers during rock weathering (NH4) 2SO4, NH4Cl]. When NH4 + is absorbed by crops, the acid radicals (SO4-2, Clˉ) often left in the soil can increase the soil acidity.
The sources of OHˉ are mainly the hydrolysis of sodium carbonate, sodium bicarbonate and other salts in the soil and the substitution of sodium in soil colloids to form strong alkali conversion results.
For example: Na2CO3 + 2H2O 2NaOH + H2CO3
NaHCO3 + H2O NaOH + H2CO3
② crop adaptability to soil pH: strong acid and alkaline soil are not conducive to crop growth. Different crops require different soil pH. Such as tea tree is only suitable for growth in acidic soil, such as azalea, massoniana, red bayberry, garlic dishes, is the indicator of acid soil plants; and Tianzhu, round cypress, cypress wood is an indicator of calcareous soil.
In addition, soil pH has a great influence on the availability of nutrients and the activities of beneficial microorganisms. Soil over-base also affects the formation of well-structured soil (now without elaborating), and these undoubtedly directly or indirectly affect Crop growth and development.
(5) Soil cushioning properties: The ability of the soil to resist the acidification or alkalization of the soil solution after the addition of acid and alkali substances in the soil is referred to as the soil buffer performance. Substitution of soil colloids exist on the cation, a buffer effect on the acid.
This is because the substitution of soil colloids (base ions or H +) is substituted into the solution to form neutral salts or H 2 O, which can make the soil pH stable and provide good environmental conditions for the growth of crops and microorganisms , But also provide the basis for guiding fertilization. The application of organic fertilizers, soil (pond mud) fertilizers, lime and green manure to soils are all effective measures to improve soil cushioning properties.