How is high-quality organic fertilizer produced?

Any qualified and high-quality organic fertilizer must be fermented by composting. Composting is a process of degrading and stabilizing organic matter under certain conditions through the action of microorganisms, and producing products suitable for land use. Composting, as an ancient and simple method to treat organic wastes and make fertilizers, has been attached great importance by all countries with the deepening of research and improvement of methods, because it has good ecological significance and brought benefits to agricultural production. There are many reports that using decomposed compost to prepare seed seedbeds can inhibit soil-borne diseases. Moreover, after the high temperature stage of composting process, antagonistic bacteria can make the number of bacteria reach a high level; Under the action of microorganisms, all organic matter in the composting process has reached a state of being difficult to decompose, stable and easily absorbed by crops; At the same time, the role of microorganisms can reduce the toxicity of heavy metals in a certain range. It can be seen that composting is a simple and effective method to make bio-organic fertilizer, which is beneficial to the development of ecological agriculture.

Most organic fertilizer products in China only have compost fermentation 15-20 days, which can only reach the harmless standard. The fermentation process of high-quality organic manure compost usually takes 45-60 days. This is because harmful microorganisms such as plant pathogens, eggs and weed seeds will be killed in the heating stage and high temperature stage in the early stage of composting, but the main function of microorganisms in this process is metabolism and reproduction, and only a small amount of metabolites will be produced, which are unstable and not easily absorbed by plants. It takes 45-60 days for microorganisms to decompose organic matter and produce a large number of metabolites beneficial to plant growth and absorption in the later stage of cooling. Composting can achieve three purposes through this process, one is harmless; The second is humus; Third, a large number of microbial metabolites such as various antibiotics, protein, etc. Why does compost produce such an effect? The principle of composting is introduced in detail below.

First, the principle of organic fertilizer fermentation

1, the transformation of organic matter during composting

The complex transformation of organic matter in compost under the action of microorganisms can be summarized as two processes: one is the mineralization process of organic matter, that is, the complex organic matter is decomposed into simple substances, and finally carbon dioxide, water and mineral nutrients are generated; The other is the humification process of organic matter, that is, the decomposition and synthesis of organic matter produce more complex special organic matter-humus. These two processes are carried out simultaneously, but in opposite directions. Under different conditions, the intensity of each process is obviously different.

2. Mineralization of organic matter

(1) Polysaccharide compounds (starch, cellulose and hemicellulose) decomposed by nitrogen-free organic matter are first hydrolyzed into monosaccharides under the action of hydrolases secreted by microorganisms. Glucose decomposes rapidly under the condition of good ventilation, and intermediate products such as alcohol, acetic acid and oxalic acid are not easy to accumulate, eventually forming CO2 and H2O, and releasing a lot of heat energy. If there is poor ventilation, monosaccharides will slowly decompose under the action of anaerobic microorganisms, producing less heat and accumulating some intermediate products-organic acids. When microorganisms are extremely anaerobic, reducing substances such as CH4 and H2 will also be generated.

(2) Decomposition of Nitrogen-containing Organic Matter The nitrogen-containing organic matter in compost includes protein, amino acids, alkaloids and humus. Except humus, most of them are easy to decompose. Protein, for example, is gradually degraded by protease secreted by microorganisms to produce various amino acids, and then ammoniated and nitrated to form ammonium salts and nitrates respectively, which can be absorbed and utilized by plants.

(3) Phosphorus-containing organic matter in compost is transformed into phosphoric acid under the action of various saprophytic microorganisms, which becomes a nutrient that plants can absorb and utilize.

(4) Transformation of sulfur-containing organic matter in compost, which generates hydrogen sulfide under the action of microorganisms. Hydrogen sulfide is easy to accumulate in anaerobic environment, which will be toxic to plants and microorganisms. However, under the condition of good ventilation, hydrogen sulfide is oxidized into sulfuric acid under the action of sulfur bacteria, and reacts with alkali in compost to generate sulfate, which not only eliminates the toxicity of hydrogen sulfide, but also becomes a sulfur nutrient that plants can absorb. Under the condition of poor ventilation, anti-sulfuration occurs, which makes sulfuric acid transform into H2S, which is harmful to plants. In the process of composting fermentation, the aeration of composting can be improved and the anti-sulfur effect can be eliminated by turning over the compost regularly.

(5) The conversion of lipids and aromatic organic compounds, such as tannins and resins, has complex structure and slow decomposition, and its final products are also CO2 and water; Lignin is a particularly stable organic compound in compost containing plant raw materials (such as bark and sawdust). ). It has a complex structure, contains aromatic nuclei, exists in plant tissues in the form of polymerization, and is extremely difficult to decompose. Under well-ventilated conditions, fungi and actinomycetes are mainly decomposed slowly, and their aromatic nuclei can be transformed into quinones, which is one of the raw materials for the synthesis of humus. Of course, these substances will continue to decompose under certain conditions.

To sum up, the mineralization of compost organic matter can provide available nutrients for crops and microorganisms, provide energy for microbial activities, and prepare basic raw materials for the humification of compost organic matter. When aerobic microorganisms are the main activity of composting, organic matter mineralizes rapidly to generate more carbon dioxide, water and other nutrients, which decompose rapidly and thoroughly, releasing a lot of heat energy. When anaerobic microorganisms are the main activity, the decomposition speed of organic matter is slow and often incomplete, and less heat energy is released. Shangyi not only accumulates plant nutrients, but also accumulates organic acids and reducing substances such as CH4, H2S, PH3 and H2, which will be unfavorable or even harmful to crop growth to a certain extent. Therefore, the purpose of composting during fermentation is to change the types of microbial activities and eliminate harmful substances.

3. Humidification process of organic matter

There are many theories about the formation process of humus, which can be roughly divided into two stages: in the first stage, organic residues are decomposed to form the original substances that constitute humus molecules, such as polyphenols and nitrogen-containing organic substances (amino acids, peptides, etc. ); In the second stage, polyphenol oxidase secreted by microorganisms oxidizes polyphenols into quinones, and then quinones condense with amino acids or peptides to form humus monomers. Because there are many kinds of phenols, quinones and amino acids, and the condensation methods are different, the humus monomers formed are also diverse. Under different conditions, these monomers further condense to form molecules of different sizes.

Second, the composting fermentation process

Composting is actually a form of waste stabilization, but it needs special humidity, ventilation conditions and microorganisms to produce suitable temperature. It is generally believed that this temperature is higher than 45℃, and maintaining this high temperature can inactivate pathogenic bacteria and kill weed seeds. After reasonable composting, the decomposition rate of residual organic matter is low, relatively stable and easy to be absorbed by plants. The odor can be greatly reduced after composting. There are many different kinds of microorganisms involved in the composting process. Due to the change of raw materials and conditions, the number of various microorganisms is constantly changing, so no microorganism always occupies a dominant position in the composting process. Each environment has its own specific microbial flora, and the diversity of microorganisms makes composting avoid system collapse when external conditions change.

The composting process is mainly carried out by microorganisms, and microorganisms are the main body of composting fermentation. There are two sources of microorganisms involved in composting: one is a large number of microorganisms in organic waste; The other is an artificially added microbial agent. These strains have strong decomposition ability to some organic wastes under certain conditions, and have the characteristics of strong activity, fast reproduction and fast decomposition of organic matter, which can accelerate the composting reaction process and shorten the composting reaction time.

Compost is generally divided into aerobic compost and anaerobic compost. Aerobic composting is the decomposition process of organic matter under aerobic conditions, and its metabolites are mainly carbon dioxide, water and heat. Anaerobic composting is the decomposition process of organic matter under anaerobic conditions. The final metabolites of anaerobic decomposition are methane, carbon dioxide and many low molecular weight intermediates, such as organic acids. The microorganisms involved in the composting process are mainly bacteria, fungi and actinomycetes. These three kinds of microorganisms have psychrophiles and thermophilic bacteria. In the process of composting, the microbial population changes alternately with the change of temperature, which shows that the low-temperature and medium-temperature flora changes to the medium-high temperature flora, and the medium-high temperature flora changes to the medium-low temperature flora. With the extension of composting time, bacteria gradually decreased, actinomycetes gradually increased, and mold and yeast decreased significantly at the end of composting.

Third, the fermentation process of organic compost can be simply divided into the following four stages.

1. In the early stage of composting, the microorganisms in compost are mainly mesophilic and aerobic, and the most common ones are Bacillus, Bacillus and mold. They start the fermentation process of compost and decompose easily decomposed organic substances (such as monosaccharide, starch, protein, etc. ) under aerobic conditions, a lot of heat is generated, and the composting temperature is continuously increased from about 20 to about 40, which is called heating stage, or medium temperature stage.

2. In the high temperature stage, with the increase of temperature, thermophilic microorganisms gradually replaced mesophilic species to play a leading role, and the temperature continued to rise, reaching more than 50 in a few days, and entered the high temperature stage. In the high temperature stage, thermophilic actinomycetes and thermophilic fungi become the main species. They strongly decompose complex organic substances (such as cellulose, hemicellulose, pectin, etc. In composting, heat is accumulated, and the composting temperature rises to 60-70, even as high as 80. Immediately, most thermophilic microorganisms also died or went into a dormant state (more than 20 days), which played an important role in accelerating the decomposition of compost. Compost with improper composting only has a short high temperature period, or it can't reach high temperature at all, so it decomposes slowly, and it can't reach semi-decomposed state for half a year or even longer.

3. Cooling stage When the high temperature stage lasts for a certain period of time, most cellulose, hemicellulose and pectin substances have been decomposed, leaving complex components (such as lignin) and newly formed humus, the activity of microorganisms is weakened and the temperature is gradually reduced. When the temperature drops below 40℃, mesophilic microorganisms become the dominant species again. If the cooling stage comes early, it means that the composting conditions are not ideal and the decomposition of plant substances is not sufficient. At this time, the pile can be turned over, and the accumulated materials can be mixed evenly, so that it can generate secondary heat and temperature rise, and promote the decomposition of compost.

4. In the stage of composting and fertilizer conservation, after composting, the volume is reduced and the heap temperature is slightly higher than the air temperature. At this time, the compost should be compacted to produce anaerobic state, which weakens the mineralization of organic matter and is beneficial to fertilizer conservation. In short, the fermentation process of organic compost is actually the metabolism and reproduction process of various microorganisms. The metabolic process of microorganisms is the process of organic matter decomposition. The decomposition of organic matter will inevitably produce energy, promote the composting process, raise the temperature and dry the wet substrate. Many compost substrates carry pathogens from humans, animals and plants, as well as annoying organisms such as weed seeds. In the process of composting, the growth of these organisms can be effectively controlled by continuous heating for a short time.

Therefore, one of the main advantages of high-temperature composting is that it can inactivate human, animal and plant pathogens and seeds. The inactivation of pathogens and seeds is due to their cell death, which is largely based on the thermal inactivation of enzymes. The inactivation of enzyme is reversible at a proper temperature, but irreversible at a high temperature. In a small temperature range, the active part of the enzyme will decrease rapidly. Without the action of enzymes, cells will lose their functions and then die. Only a few enzymes can resist high temperature for a long time. Therefore, microorganisms are very sensitive to thermal inactivation.

Studies have shown that heating at a certain temperature for a period of time can destroy pathogens or annoying organisms. Usually, it is heated for 5- 10min at the temperature of 60-70 (wet and hot). It can destroy the activity of non-dormant bodies of non-spore fungi and spore fungi. Sterilization at 70℃ for 30 minutes can eliminate pathogens in sludge. But at lower temperature (50-60℃), some pathogenic bacteria can be inactivated for 60 days. Therefore, it is necessary to keep the temperature above 60℃ for a period of time during composting. In the process of composting, the pile should be turned over when necessary. Generally, it is carried out when the reactor temperature crosses the peak and begins to cool down. Turning the pile can make the substances with different decomposition temperatures in the inner and outer layers mix evenly again. If the humidity is insufficient, some water can be added to promote the uniform decomposition of compost. In the process of composting, all kinds of organisms and microorganisms die, replace and transform their material forms at the same time. The above block introduction briefly introduces the fermentation principle of compost from different angles. No matter from the point of view of thermodynamics, biology or material transformation, these reactions can't be completed in a few days or even less, which is why compost still has to go through 45-60 degrees even under the premise of well-controlled temperature, humidity, moisture, microorganisms and other conditions.