Relationship among soil, humic acid, and microorganisms
The soil is alive, and this life is the soil microbe. As we all know, soil is the base of microbes and a natural medium for microbial growth and reproduction. Humic acid runs through the life of the soil and is the “nucleus of life” of the soil. Without humic acid, the soil will lose its activity. Based on this, clarifying the relationship between “soil-humic acid-microorganism” has important practical significance for protecting land resources and promoting sustainable soil production.
Humic acid is the deepest “dark matter” in the soil, and every cycle of its life is associated with the living body.
1 by life: mainly from animal and plant residues (mainly plant residues) as material sources;
2 by living body transformation: mainly through the participation and role of microorganisms, continuous decomposition, transformation, synthesis;
3Return to the living body: mainly feed back the living body through the soil humic acid, promote the growth of green plants (producers), enhance the immunity of livestock, aquatic products, humans (consumers), and provide nutrients and energy for microorganisms (decomposers). source.
According to this, humic acid is accompanied by the beat of life, and realizes the cycle of “survival → transformation → extinction → rebirth”, and according to its existence, it becomes the radiance of the vitality of the soil.
The structural characteristics of the soil include three layers of meaning:
1 In the process of soil formation, organic matter and minerals form organic-inorganic composites, microaggregates, large agglomerates, etc.;
2 The microaggregates are the core of the soil structure, and are the structural units (equivalent to the cells in the soil) that the soil exerts its least function and can exist independently;
3 The soil structure during soil utilization has a great impact on soil function.
Microaggregates are the key to the structural stability of the “soil house”, and humic acid is a key component in the construction of “micro houses”. In the process of soil formation, humic acid and organic macromolecules such as polysaccharides such as barium sulphonate secreted by various microorganisms, clay minerals, and hydroxides of iron and aluminum are combined with various forces through various forms to form various kinds. Types of organic-inorganic composites.
At the same time, microaggregates of different grain sizes are formed by agglomeration under various surface charges and forces. Accordingly, the formation process of humic acid microaggregates endows the fresh vitality of the soil organic-inorganic composite, which is the core and key to stabilize the soil structure.
The functions of soil ecosystems mainly include: the ability and level of material conversion and energy circulation in soil, the activity of soil organisms, the balance of nutrients and water in soil and its impact on the environment. Humic acid is the most active part of soil organic matter and plays a vital role in soil ecosystem material circulation and energy conversion.
1 active participants and promoters of soil formation and soil fertility;
2 promote and restrict the migration, fixation and leaching of metal ions and trace elements in soil;
3 is a stabilizer for soil structure;
4 affecting the salt exchange capacity of the soil;
5 affecting the water holding capacity of the soil;
6 is a warehouse for plant materials.
According to this, humic acid can regulate the material circulation, energy conversion and information transmission between biological systems, soil systems and environmental systems, and is an important substance for maintaining soil function stability.
- Soil microorganisms
(1) Soil microbial composition
Soil is the base of microbes and a natural “medium” for microbial growth and reproduction. Soil microorganisms are a general term for bacteria, fungi, actinomycetes, algae, etc. that live in the soil and are important components of the soil. The individual is small, usually calculated in micrometers or nanometers, and its type and quantity vary with the soil environment and soil depth.
Among them, bacteria are the most, actinomycetes and fungi are second, and algae are less. It is estimated that there are thousands or even tens of thousands of species per gram of soil, ranging from several hundred to several billion microbial individuals, the type and quantity of which vary with the soil environment and the depth of the soil layer.
Generally speaking, in the soil per gram of cultivated layer, the number of bacteria is about 10^8~10^9, the number of actinomycetes is about 10^7~10^8, and the number of fungi is about 10^5~10^. Six, the number of algae is about 10^4~10^5, they all live in the soil.
(2) Soil microbial effects
Soil microbes have a major impact on soil formation and development, material circulation, fertility evolution, and plant growth.
1 bacteria: suitable for neutral and slightly alkaline living conditions. Among them, autotrophic bacteria have the ability to assimilate carbon dioxide, directly affect the physical and chemical properties of the soil, and balance the pH of the soil; heterotrophic bacteria exist in a state of symbiosis with crops, and directly promote the growth of crops, such as rhizobium of leguminous plants. In addition, it has a strong nitrogen fixation effect, which produces a significant yield increase effect in the case of less nitrogen application.
2 Actinomycetes: suitable for neutral and slightly alkaline living conditions. Actinomycetes in the soil live in aerobic heterotrophic state. Their main activities are to decompose the cellulose, lignin and pectin in the soil. These effects can improve the nutrient status of the soil and facilitate direct crops. Absorb and utilize soil nutrients.
3 fungi: suitable for slightly acidic living conditions. Participation in the decomposition of animal and plant residues becomes an indispensable driving force for nitrogen and carbon cycling in the soil. Especially in the early stage of decomposition of plant organisms, fungi are more active than bacteria and actinomycetes.
4 algae: a type of single-celled organism, mainly in the aquatic environment. The cyanobacteria in the algae also have the effect of fixing nitrogen in the air. It is more suitable for functioning in an alkaline environment.
(3) Soil microbial vigor
Soil microbes are not only an important part of the soil, but also the vitality of the soil ecosystem.
1 gases and organic acids produced by various types of microbial metabolism contribute to the formation of soil aggregate structure;
2 Decompose organic matter, synthesize soil humus-humic acid, and fertilize the soil;
3 Decompose minerals and promote the dissolution of poorly soluble substances in the soil (such as phosphorus bacteria, potassium bacteria, etc.);
4 fix atmospheric nitrogen and increase soil nitrogen nutrients;
5 to regulate plant growth, such as rhizobium, mycorrhiza, fungi, etc. that are symbiotic with plants;
6 secrete antibiotics (such as actinomycetes) to prevent soil-borne diseases;
7 secrete a large number of enzymes to promote the conversion of soil nutrients;
8 Degradation of organic pesticides, urban pollutants and factory waste in the soil.
The above eight items reflect the important relationship between soil microbes and soil fertility, soil health and plant growth, and are the main force of material circulation and energy flow in soil ecosystems.
- Soil humic acid and microorganisms
(1) Microbiological mechanism of soil humic acid formation
There are seven hypotheses about the microbiological mechanism of humic acid formation:
1 Waxman theory that in the formation of humus, nitrogen-containing organic matter and nitrogen-free organic matter are decomposed by aerobic microorganisms to produce microbial organisms (soil protein) and lignin, which are then combined with alkali to form humus soil.
2 Williams theory that humic acid is a secretion of soil microorganisms;
3 The microbial synthesis hypothesis is that microbes use plants as carbon sources and energy sources to synthesize polymer humic substances in cells, which are released into the soil after death, and then degraded into humic acid and fulvic acid outside the cells;
4 cell autolysis hypothesis that humus is the autolysis product of plants and microorganisms after death;
5 Coal Chemistry believes that there are two main conditions affecting the accumulation of plant residues in the marshes and the formation of peat. One is the physical condition that isolates the plant residues from the air, and the other is the chemical conditions that maintain the good activities of the microorganisms;
6 Kononova theory believes that the formation of humus includes two stages of “decomposition-condensation”, with the participation of soil microbes;
7 Anaerobic fermentation theory that humic acid formation includes three stages of “hydrolysis – acid production – synthesis”, and the role of microorganisms is mentioned to varying degrees.
Regardless of which hypothesis, the important role of microorganisms in the formation of humic acid is fully affirmed.
(2) Humic acid efficacy of soil microbial reproduction
The formation of humic acid is inseparable from soil microbes, and the reproduction of soil microorganisms is also inseparable from humic acid.
1 Humic acid provides a source of material and energy for soil microorganisms. Soil microbial nutrition mainly includes carbon, hydrogen, oxygen, nitrogen and some mineral elements. Humic acid contains carbon, oxygen, hydrogen, nitrogen and other elements, which can provide carbon and nitrogen sources for soil microorganisms for survival and reproduction.
2 Humic acid creates a suitable living environment for soil microorganisms. Soil microbial survival requires appropriate temperature, humidity, pH, and the like. Humic acid can directly or indirectly improve soil temperature, moisture and gas permeability, regulate soil pH, promote soil microbial growth and reproduction, and increase its quantity and variety.
3 Humic acid provides a living home for soil microorganisms. The total number of microorganisms in soils with deep soil layers, loose soil, good physical properties and abundant nutrient content is also high. Humic acid is the core of soil fertility, and humic acid is good for soil and fertilizer;
(3) Humic acid and microorganisms are the soil life community
Humic acid is the carrier of soil life. It provides carbon sources and nitrogen sources for microbes and promotes them for life. It promotes the quantity, variety and diversity of microorganisms. Microorganisms are the embodiment of soil life and act as decomposers. It is indispensable for the formation and decomposition of humic acid.
The formation of humic acid is inseparable from soil microbes. The survival and reproduction of soil microbes cannot be separated from humic acid. The two are interdependent and promote the formation and development of soil, fertility evolution, material circulation and energy conversion. It can be seen that the “soil-humic acid-microorganism” is inseparable and belongs to the community of life.