How should you choose a microbial fertilizer? Is it true that the higher the bacterial count, the better?

　　Microbial fertilizers are developing rapidly, but product quality varies considerably. To choose a reputable brand or product, we need to consider several factors, which can be summarized as “three checks.”

　　Check the product’s expiration date.

　　Microbial fertilizers all have a specified shelf life; once this period has passed, the microbial activity in the product is significantly reduced. Typically, conventional microbial fertilizers have a shelf life of about 12 months, though the exact duration can vary depending on the specific product.

　　Second, verify that the viable bacterial count complies with national regulations.

　　According to national standards, the viable bacterial count in microbial inoculants must be ≥200 million per gram, while that in compound microbial fertilizers and bio-organic fertilizers must be ≥20 million per gram. Products falling below these thresholds are generally considered non‑compliant. Of course, high‑concentration microbial fertilizers also exist.

　　Third, assess the actual soil conditions to determine whether phosphorus and potassium levels exceed the permissible limits.

　　It is essential to apply fertilizers according to soil conditions. If the soil’s phosphorus and potassium levels are significantly excessive, one should reduce or avoid using fertilizers containing these nutrients and instead rely on microbial fertilizers that solubilize phosphorus and potassium, thereby mitigating soil salinization and lowering the concentrations of phosphorus and potassium.

　　If the soil is low in phosphorus and potassium, apply a phosphate‑potassium fertilizer together with a microbial fertilizer, such as a multi‑spore inoculant, to reduce the soil’s fixation of these nutrients and thereby meet the nutritional needs of vegetable growth, promoting vegetative development.

　　Is it better to have a higher bacterial count in fertilizer?

　　Not at all! The efficacy of microbial fertilizers is influenced by the growth characteristics of different microbial strains. Haphazardly combining strains can easily lead to antagonism among them, thereby compromising performance. Quantity alone does not tell the whole story—what matters is not just the total number of microbes, but the count of viable, active ones. Only live, active microorganisms exert their beneficial effects; the greater the population of such beneficial strains, the more pronounced the results will be.

　　In addition to the type and quantity of microorganisms, the purity of the microbial strain is critical in determining product performance. When the levels of molds and other contaminant microorganisms, as well as their contamination rate, exceed acceptable limits, application efficacy can be compromised. Some substandard products on the market may harbor pathogenic bacteria; intended to restore soil health through beneficial microbes, they can inadvertently promote the proliferation of pathogens, leading to disease outbreaks.