After the release of "Zero Growth of Chemical Fertilizers", microbial fertilizer has become the new darling of the fertilizer industry this year. So, what exactly does microbial fertilizer consist of?

What constitutes microbial fertilizer and its shelf life

1. How to select carriers according to local conditions?

II. Why is the safety of raw materials and auxiliary materials crucial for ensuring microbial fertilizers?

III. How to extend the shelf life of microbial fertilizer products?

1. How to select carriers according to local conditions? What are the carriers?

Apart from pure microbial agents produced through freeze-drying, commercial microbial fertilizers generally incorporate certain easily obtainable raw materials as carriers for the microbial cells, to varying degrees. Some carriers can enhance the viability of the microbial cells, facilitating processing, storage, transportation, and field application.

When selecting carriers, attention should be paid to their physicochemical properties, such as moderate pH, avoiding carriers that are too acidic or alkaline, appropriate particle size, good adsorption capacity, and low osmotic pressure.

The carriers used in microbial fertilizers can be divided into inorganic carriers, organic carriers, and organic-inorganic mixed carriers.

Inorganic carriers such as diatomaceous earth, zeolite powder, ore powder, bentonite, and neutral clay are inexpensive and readily available. Some, like diatomaceous earth and zeolite powder, also exhibit excellent adsorption properties. Fungi agents made from inorganic carriers are suitable for soils with high organic matter content.

Zeolite powder

After adsorbing the bacterial cells, it is easy to process into powdered bacterial fertilizer, which is convenient for mixing with organic and inorganic fertilizers for granulation. However, some inorganic carriers affect the survival rate of the bacterial cells, and when used for sprinkler irrigation or drip irrigation, they tend to stratify, deposit, and clog the pipes. When applied to barren soil lacking organic matter, the effect is not satisfactory.

There is a wide variety of organic carriers, such as bran, straw powder, distillers grains powder, starch, and fully fermented organic fertilizers. Organic carriers have strong adsorption capacity for bacterial cells and provide certain nutritional functions to the cells, which is beneficial for maintaining a high survival rate of the cells. They show quick effects when applied in the field. However, organic carriers should be dry and free from mold, and it is best to sterilize them before use to avoid contamination by miscellaneous bacteria. They also have the disadvantage of easily clogging pipes when used for sprinkler irrigation and drip irrigation. This defect can be solved by using organic carriers that are easily soluble in water.

Organic-inorganic hybrid carriers, with peat being a typical example, exhibit strong adsorption capacity for bacterial cells and a high survival rate for these cells. However, due to certain resource constraints, peat extraction has been prohibited in some regions. By mixing the aforementioned inorganic carriers with organic carriers, we can overcome the deficiency of pure inorganic carriers lacking initial nutrients, while also addressing the issue of high processing costs associated with pure organic carriers. It is crucial in carrier selection to ensure that the carrier is not contaminated by miscellaneous bacteria, especially avoiding the use of moldy agricultural by-products as carriers.

Peat

II. Why is the safety of raw materials and auxiliary materials crucial for ensuring microbial fertilizers?

Raw materials and auxiliary materials have a significant impact on maintaining microbial survival, efficacy, and safety in products, and are also one of the main components of the product. It is clarified that raw materials and auxiliary materials used in the production of bio-fertilizers should comply with the following regulations: livestock manure, animal and plant residues, and offcuts processed from animal and plant products as raw materials must be fermented and composted and meet the requirements for harmlessness before they can be used as raw materials and auxiliary materials for the production of microbial fertilizers; it is not advisable to use materials such as fly ash and other mineralized carbon, as well as waste plastic powder and other chemically synthesized carbon materials, for the production of bio-fertilizers; it is also not advisable to use raw materials that pose biological safety hazards, such as antibiotic industrial waste residue rich in protein content, which can induce the growth of drug-resistant pathogens when applied to the field. Enterprises are required to use raw materials and auxiliary materials in accordance with regulations, clarify them when applying for product registration, and have them dynamically tracked by the registration department to avoid safety hazards caused by excessive levels of heavy metals, pathogens, antibiotics, etc. in raw materials and auxiliary materials.

In microbial fertilizer products, more than 95% to 98% consists of raw materials, auxiliary materials, and other carrier materials. These materials are crucial for ensuring product quality, safety, and effectiveness, as they are not merely carriers but also serve as the "food" for microorganisms. They provide not only the materials for the production of microorganisms and their metabolites but also the energy for microbial growth, metabolism, and reproduction. Specifically, microorganisms can only proliferate significantly when they have accessible organic sources, which provide the energy for metabolism, nitrogen fixation, and the activation of potassium and phosphorus minerals. They can also synthesize active substances such as polysaccharides, polyamino acids, and biological hormones, forming soil aggregate structures with functions such as nutrient retention, water retention, and aeration. Good organic matter can be fermented and decomposed by microorganisms. The carbon source contained in such organic matter is commonly referred to as fermentable carbon. The type of organic matter carrier (fermentable carbon) that can be decomposed by microorganisms is directly related to its source. Therefore, it is necessary to clarify the sources and types of various raw materials, auxiliary materials, and other organic carriers used in microbial fertilizers, which also facilitates the regulation of their safety. Conversely, the reason why microbial fertilizers made with inorganic materials such as bentonite, diatomaceous earth, and fly ash as carriers (or adsorbents) exhibit slow or even insignificant fertilizing effects is the lack of organic matter carriers (fermentable carbon) for microbial growth.

Currently, there is a wide variety of raw and auxiliary materials used in the production of microbial fertilizers. Besides traditional agricultural wastes such as fermented livestock and poultry manure and straw, in recent years, materials such as monosodium glutamate, leftover materials from the sugar and paper industries, household waste, urban sludge, bentonite, diatomaceous earth, coal powder, lignite, and nutrient soil have also been utilized. These materials have complex compositions and pose safety hazards such as heavy metal, pathogenic bacteria, and antibiotic residues. Currently, excessive heavy metal content has attracted widespread social attention, especially in edible agricultural products. The extensive application of organic fertilizers containing high levels of heavy metals has led to a rapid increase in soil heavy metal content, which must be given sufficient attention. The microorganisms used in the production of microbial fertilizers are safe, and the safety hazards of microbial fertilizers are often caused by insufficiently strict control of raw and auxiliary materials.

III. How to extend the shelf life of microbial fertilizer products?

The shelf life standards for microbial fertilizer products and agricultural industry standards require at least three months or more. In fact, from the production factory to the farmers application in the field, there is a certain process of storage, transportation, and sales, which takes about six months. Except for tropical regions, the peak fertilization period for planting in China is twice a year. In many areas of the northeast and northwest regions, there is only one peak fertilization period. As a circulating commodity, the ideal shelf life of microbial fertilizer should be 18 months. It can still be used in the second year if it has not been applied to the farmland for one year.

Microbial fertilizers are generally required to be stored in a cool and dry place. The specific storage temperature within the range of 0~15℃ has little effect on the bacterial content. Solid preparations are also unaffected below 0℃.

To extend the shelf life, different measures are taken for liquid and solid dosage forms.

The pipeline for liquid dosage forms, from the fermentation tank to the packaging bottle, must undergo sterilization during production, and the packaging bottles should also be sterilized. The packaging environment should be maintained in a semi-sterile state. If machines are used for filling, they should be located in a semi-sterile packaging workshop that has undergone sterilization treatment, and a cover should be provided above the assembly line. Before packaging, the nutrients in the liquid bacterial agent should be consumed to the lowest possible level. To facilitate the emission of metabolic gases generated during storage and transportation, using breathable but impermeable film bottle caps is an effective measure. Different bacterial species have different shelf lives, with those with protective layers (spores, spore-forming cells, capsules) having longer shelf lives.

In addition to maintaining cool and dry conditions during storage and transportation, solid dosage forms require attention to prevent contamination by miscellaneous bacteria during the production process. The packaging process and the cleanliness of the environment must be high. Choosing the appropriate carrier is important, as different carriers are required for different bacterial agents. The physicochemical properties of the carrier also need to be considered. The carrier should be sterilized and dried. Bacillus has a relatively long shelf life (with about 5% moisture content) and is less prone to contamination by miscellaneous bacteria. Non-Bacillus may be affected by low humidity, which could potentially affect the bacterial content. The possibility of mold contamination increases when the moisture content is above 10%. Some companies adopt vacuumization or nitrogen filling protective measures, which may be feasible for a small amount of products. However, whether it is feasible for large-scale production and the effectiveness of these measures are still inconclusive, and require long-term follow-up observation.

Different granulation methods can also affect the shelf life. Products granulated with a higher proportion of organic fertilizer have a longer shelf life, while those with a higher proportion of chemical fertilizer have a shorter shelf life. Products granulated with chemical fertilizer and protected measures have a longer shelf life, as do those that avoid the high-temperature drying process during granulation. Products with a higher proportion of organic components in extrusion granulation have a longer shelf life, while those with a higher proportion of inorganic components have a shorter shelf life. Products that undergo rolling granulation and are sprayed with microbial agents after drying have a relatively longer shelf life. After leaving the factory, in addition to providing cool and dry storage and transportation conditions, direct sunlight exposure should be avoided.