Soil is alive, and this life is soil microorganisms. We all know that soil is the base camp of microorganisms and a natural medium for the growth and reproduction of microorganisms. Humic acid runs through the life of the soil and is the “core of life” of the soil. Without humic acid, the soil will lose its vitality. Accordingly, it is of great significance to clarify the relationship between “soil-humic acid-microbes” for the protection of land resources and promotion of sustainable soil production.
1. Soil humic acid
01- Soil is the essence of life
Humic acid is the deepest “dark substance” in the soil, and every cycle of its life is associated with living organisms.
1) Born of living beings:
Mainly use animal and plant residues (mainly plant residues) as material sources
2) Transformation through life forms:
Mainly through the participation and function of microorganisms, it continuously decomposes, transforms, and synthesizes;
3) Return to the living body:
It mainly feeds life through soil humic acid, promotes the growth of green plants (producers), enhances the immunity of livestock, poultry, aquatic products and people (consumers), and provides nutrients and energy for microorganisms (decomposers).
Accordingly, humic acid, along with the rhythm of life, realizes the cycle of “survival→transformation→death→rebirth”, and becomes the essence of radiating the vitality of soil life according to its existence.
02 Core of Soil Structure
The structural properties of soil include three levels of meaning:
1) In the process of soil formation, organic matter and minerals form organic-inorganic complexes, micro-aggregates, macro-aggregates, etc.;
2) Microaggregates are the core of soil structure, and they are the smallest structural units that can exist independently;
3) The structure of soil in the process of soil utilization has a great influence on the function of soil.
Micro-aggregates are the key to the stability of the “soil house” structure, and humic acid is the key component to construct the soil “micro-house”. In the process of soil formation, humic acid, organic macromolecules such as polyuronic acid glycosides secreted by various microorganisms, clay minerals, and hydroxides of iron and aluminum, etc., combine with various forces in different forms to form various soils. Types of organic-inorganic complexes.
At the same time, under various surface charges and forces, microaggregates of different particle sizes were formed through agglomeration. Accordingly, the formation process of humic acid micro-aggregates endows the organic-inorganic complex with fresh vitality. And is the core and key to stabilizing the soil structure.
03 Essentials of Soil Functions
The functions of the soil ecosystem mainly include: the ability and level of material conversion and energy circulation in the soil, the activity of soil organisms, the balance of nutrients and water in the soil, and their impact on the environment. Humic acid is the most active part of soil organic matter and plays a vital role in the material cycle and energy conversion of the soil ecosystem.
- ①Active participant and facilitator of soil formation and soil fertility;
- ② Promote and restrict the migration, fixation and leaching of soil metal ions and trace elements;
- ③It is a stabilizer of soil structure;
- ④ Affects the base exchange capacity of the soil;
- ⑤ affect the water holding capacity of the soil;
- ⑥It is the warehouse of plant materials.
Humic acid can regulate the material cycle, energy conversion and information transmission among biological systems, soil systems and environmental systems. And is an important substance to maintain the stability of soil functions.
2. Soil microorganisms
01 Soil microbial composition
Soil is the base camp of microorganisms and the natural “medium” for the growth and reproduction of microorganisms. Soil microorganisms are the general term for bacteria, fungi, actinomycetes, algae, etc. living in soil, and are important components of soil. Its individuals are tiny, generally calculated in micrometers or nanometers, and its types and quantities vary with soil-forming environments and soil depths.
Among them, bacteria are the most, followed by actinomycetes and fungi, and algae are less. It is estimated that there are thousands or even tens of thousands of species per gram of soil, about hundreds of millions to billions of microbial individuals, and their types and quantities vary with the soil-forming environment and the depth of the soil layer.
Generally speaking, in each gram of plow layer soil, 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^ 6, the number of algae is about 10^4~10^5, and they all live in the soil.
02 Soil microbial action
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, which directly promote the growth of crops, such as rhizobium of leguminous plants etc., have a strong nitrogen fixation effect, and produce a significant increase in yield under the condition of less nitrogen fertilizer.
2) Actinomycetes
Suitable for neutral and slightly alkaline living conditions. Actinomycetes live in an aerobic heterotrophic state in the soil, and their main activity is to decompose cellulose, lignin and pectin in the soil, and through these actions to improve the nutrient status of the soil, it is convenient for crops to directly Absorb and utilize soil nutrients.
3) Fungi
Suitable for slightly acidic living conditions. Participate in the decomposition of animal and plant residues and become an indispensable driving force for nitrogen and carbon cycles in the soil. Especially in the early stages of plant organism decomposition, fungi are more active than bacteria and actinomycetes.
4) Algae
It is a class of single-celled organisms mainly found in aquatic environments. Cyanobacteria in algae also have the function of fixing nitrogen in the air. It is more suitable for functioning in an alkaline environment.
03 Soil microbial activity
Soil microorganisms are not only an important part of soil, but also the vitality of soil ecosystem.
- ①The gases and organic acids produced by the metabolism of various microorganisms contribute to the formation of soil aggregate structure;
- ②Decompose organic matter, synthesize soil humus-humic acid, and fertilize the soil;
- ③Decompose minerals and promote the dissolution of insoluble substances in the soil (such as phosphorus bacteria, potassium bacteria, etc.);
- ④ Fix atmospheric nitrogen and increase soil nitrogen nutrient;
- ⑤ Regulating plant growth, such as rhizobia, mycorrhizae, fungi, etc. that are symbiotic with plants;
- ⑥ Secrete antibiotics (such as actinomycetes) to prevent soil-borne diseases;
- ⑦ Secrete a large amount of enzymes to promote the transformation of soil nutrients;
- ⑧degradation of organic pesticides, urban pollutants and factory wastes left in the soil.
The above 8 items reflect the important relationship between soil microorganisms and soil fertility, soil health, and plant growth, and are the main force of material circulation and energy flow in soil ecosystems.
3. Soil humic acid and microorganisms
01 Microbiological mechanism of soil humic acid formation
There are seven hypotheses about the microbiological mechanism of humic acid formation:
- ①Waksman theory believes that during the formation of humus by plants, nitrogen-containing organic matter and nitrogen-free organic matter are decomposed by aerobic microorganisms to produce microorganisms (soil protein) and lignin, which are then combined with alkali to form humus.
- ②Williams theory believes that humic acid is the secretion of soil microorganisms;
- ③ The microbial synthesis hypothesis believes that microorganisms use plants as carbon sources and energy sources to synthesize high-molecular humus substances in cells, release them into the soil after death, and degrade them into humic acid and fulvic acid outside the cells;
- ④The cell autolysis hypothesis believes that humus is the product of cell autolysis after the death of plants and microorganisms;
- ⑤ Coal chemistry theory believes that there are two main conditions that affect the accumulation of plant residues in swamps and the formation of peat, one is the physical conditions that isolate plant residues from the air, and the other is the chemical conditions that maintain the good activities of microorganisms;
- ⑥Kononova’s theory believes that the formation of humus includes two stages of “decomposition-condensation”, both of which involve the participation of soil microorganisms;
- ⑦ The theory of anaerobic fermentation believes that the formation of humic acid 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.
02 The effect of humic acid on the reproduction of soil microorganisms
The formation of humic acid is inseparable from soil microorganisms, and the reproduction of soil microorganisms is also inseparable from humic acid.
- ① Humic acid provides material and energy sources 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 to survive and reproduce.
- ② Humic acid creates a suitable living environment for soil microorganisms. Soil microorganisms need suitable temperature, humidity and pH to survive. Humic acid can directly or indirectly improve soil temperature, moisture and air permeability, adjust soil pH, promote the growth and reproduction of soil microorganisms, and increase their number and types.
- ③Humic acid provides a living home for soil microorganisms. The total number of microorganisms in the soil with deep soil layer, loose soil quality, better physical properties and richer available nutrients is also higher. Humic acid is the core of soil fertility, when humic acid prospers, soil fertilizes; when soil fertilizes, microorganisms prosper.
03 Humic acid and microorganisms are both soil life communities
Humic acid is the carrier of soil life. It can provide carbon and nitrogen sources for microorganisms and accompanying them for life. And it can promot the number, type and diversity of microorganisms. The microorganisms are the embodiment of soil life and play the role of decomposers. The formation and decomposition of humic acid is indestructible.
The formation of humic acid is inseparable from soil microorganisms. The survival and reproduction of soil microorganisms cannot be separated from humic acid. The two are interdependent and jointly promote the formation and development of soil, fertility evolution, material cycle and energy conversion. It can be seen that “soil-humic acid-microbes” are inseparable and belong to the community of life.
