First, two explanations of soil nutrients:
1. Definition in the academic community: Soil nutrients refer to the nutrients that are provided by the soil to make plants grow normally, and can be directly or indirectly absorbed by plants.
2. Definition in the reference book: soil nutrients are divided into a large number of elements, middle elements and trace elements. Including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), boron (B), molybdenum (Mo), zinc (Zn) , Manganese (Mn), Copper (Cu) and Chlorine (Cl) 13 elements.
Second, soil nutrient classification:
1, according to the chemical form: organic and inorganic
2. According to the state of existence: liquid dissolution, solid adsorption and solid state
3, divided by element content: a large number of elements, middle elements and trace elements
4. Absorption status of nutrient elements: available nutrients and delayed nutrients
Third, the source of soil nutrients:
1, mainly from the soil minerals and soil organic matter, followed by atmospheric precipitation, slope seepage and groundwater
2. Irrigation and fertilization
Fourth, the transformation of soil nutrients:
1, nitrogen form and transformation
(1) Form of nitrogen (0.02% - 0.3% of total nitrogen)
Inorganic nitrogen: Ammonium and nitrate ions vary widely in soil, 1-50 mg/kg.
Organic nitrogen: A, humus, and nucleoproteins, accounting for approximately 90% of total nitrogen, cannot be used by plants; B, simple proteins that are prone to mineralization; C, amino acids, and amides, are the main source of inorganic nitrogen .
Gaseous nitrogen
(2) Nitrogen conversion
The mineralization process of organic nitrogen: ammoniation, nitrification and denitrification.
Ammonium fixation: including a.2:1 type of clay minerals (illitic, montmorillonite, etc.) adsorption of ammonium ions; b.
Microorganisms absorb and assimilate into two forms of organic nitrogen.
2, Phosphorus form and transformation
(1) Morphology of phosphorus (total phosphorus in soil 0.01% - 0.2%)
Organic phosphorus: nuclear protein, lecithin, and phytate account for 15% to 80% of total phosphorus.
Inorganic phosphorus: (20% - 85% of total phosphorus). According to the solubility of inorganic phosphorus can be divided into: water-soluble phosphorus, weak acid phosphorus and inorganic inorganic phosphorus compounds.
Divided into three categories based on solubility
(2) Conversion of Phosphorus
Phosphorus effective process: The slow-acting inorganic phosphorus in soil can be converted into available phosphorus under the action of carbonic acid and organic acid; the delayed organic phosphorus is gradually released by phosphoric acid under the action of microorganisms ( Root), absorbed by microorganisms and plants.
Phosphorus fixation: In calcareous soils, available phosphorus readily forms calcium triphosphate with calcium. If there is a large amount of calcium, insoluble salts such as octacalcium phosphate and apatite can be further formed; in acidic soils, with ferric hydroxide Aluminum hydroxide colloids form iron phosphate and aluminum phosphate. When the soil pH is between 6.5 and 7.5, the degree of phosphorus availability is high.
3, potassium form and transformation
(1) The form of potassium (between 0.5% and 2.5% in terms of K2O)
Water soluble potassium
Exchangeable potassium (tens to hundreds of mg/kg)
Sustained Potassium: Potassium fixed in 2:1 clay minerals and potassium in biotite.
Insoluble potassium: Potassium in primary minerals such as potassium feldspar and muscovite. It accounts for more than 95% of total potassium. 2, conversion.
(2) Potassium conversion
Potassium-enhanced process: Insoluble potassium and slow-acting potassium are released by the action of microorganisms and organic acids. Application of silicate bacterial fertilizer can directly degrade orthoclase.
Potassium fixation: Into the caverns of clay minerals.
4, the morphology and transformation of trace elements
(1) The form of trace elements
Mineral state: It is mainly found in primary minerals and clay minerals and is difficult to dissolve.
Exchangeable ion state: mainly various cations and their hydroxyl ions, a small amount of exchangeable anions, the number generally does not exceed 10mg/kg.
Solubility: In aqueous solution, the amount is low.
Complex state: Complex formation with organic ligands, relatively stable.
(2) The conversion of trace elements
It is related to the pH of the soil. In calcareous soils, iron, zinc, manganese, copper and boron easily form insoluble salts with low effectiveness and high effectiveness in acidic soils.
V. Soil nutrient content
The nutrient content of numerous elements in cultivated land in China is: total nitrogen 0.02-0.30%; total phosphorus (P2O5) 0.01-0.20%; potassium (K2O) 0.50-2.5%. The content of other trace elements is usually in the order of a few parts per million or several hundred thousand.
Sixth, soil nutrient classification
Soil nutrients can be roughly divided into six levels: one, two, three, four, five and six in total. At the same time, soil nutrient grading was mainly conducted on the content of organic matter, total nitrogen, available phosphorus, available nitrogen and available phosphorus. Soil nutrient grading standards can be seen specifically.
Seven, soil nutrient regulation
1. Fertilization: The application of organic or inorganic fertilizers helps to supplement, balance and increase the storage of soil nutrients and the proportion of effective nutrients.
2. Rotation: Because different crops have different types and quantities of nutrient requirements, various nutrients in the soil can be used in a more balanced manner through crop rotation to avoid excessive consumption of some nutrients due to continuous cropping.
3. Tillage: It can change the status of soil moisture and air, increase the ventilation of soil, be conducive to the activities of microorganisms, promote the decomposition and mineralization of minerals and organic matter, and increase the available nitrogen, phosphorus, potassium and sulfur in soil. Etc. For example, winter tillage and sunburn can accelerate the weathering of soil minerals and help increase the content of available potassium in the soil.
4. Irrigation: Irrigation and drainage can inhibit or promote the release rate of soil nutrients.
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