How can microbial fertilizers be applied effectively during the winter, and what precautions should be taken?

　　As everyone knows, microbial fertilizers can be used for seed dressing, seed soaking, root dipping, as a base fertilizer, or as a topdressing—applied either in furrows or in planting holes. In winter, when temperatures are low, applying bio‑fertilizers not only helps mobilize nutrients that have been immobilized in the soil but also promotes root growth. So, how can microbial fertilizers be applied most effectively during the winter? And what precautions should be taken when using them in cold weather?

　　How to Apply Microbial Fertilizer Effectively in Winter

　　1. Timing: Microbial fertilizers are not conventional fertilizers; applying them 7–10 days before the crop’s critical nutrient‑uptake period and peak nutrient‑absorption phase yields the best results.

　　2. Temperature: The optimal temperature for applying microbial fertilizers is 25–37°C; application yields are poor below 5°C or above 45°C. Such products should not be applied to fields under conditions of high heat, low temperatures, or drought. Additionally, it is important to maintain soil moisture at 60%–70%—the range most favorable for nitrogen-fixing bacteria.

　　3. Location: Microbial fertilizers should not be applied to soils with high sulfur content or to paddy fields with rusty water, as sulfur can kill beneficial microorganisms. For paddy fields undergoing slurry formation, broadcast application is generally not recommended; foliar spraying tends to yield better results.

　　4. Application rates. For fields that have been fertilized with chemical fertilizers for many years, when applying microbial fertilizers, the application rates of both chemical and organic fertilizers should not be drastically reduced. This is because crops have developed a reliance on chemical fertilizers, and they cannot adapt immediately to replacing these with microbial fertilizers. Therefore, the substitution rates should be gradually increased: 30% in the second year, 40% in the third year, and 60% thereafter. Phosphorus and potassium fertilizers should only be supplemented—not reduced.

　　5. Mixing: It should be noted that microbial fertilizers must not be mixed with pesticides, herbicides, sulfur‑containing fertilizers (such as potassium sulfate), or rice straw ash, as these chemicals and fertilizers can easily kill the beneficial microorganisms. Alternatively, apply the microbial fertilizer first, wait 48 hours, and then proceed with pesticide or herbicide application. When using it for seed treatment, never mix it with seeds that have already been treated with chemical agents. Additionally, avoid blending it with uncomposted farmyard manure.

　　Precautions for Applying Microbial Fertilizer in Winter

　　First is soil moisture.

　　After applying microbial fertilizer, be sure to irrigate appropriately: on a sunny morning, use a light watering. This not only raises soil temperature but also helps vent moisture through ventilation. Following irrigation, perform shallow hoeing to improve soil aeration and permeability, thereby enhancing the effectiveness of the beneficial microorganisms.

　　Second is soil temperature.

　　It is understood that the beneficial microorganisms in microbial fertilizers are most active when soil temperatures range from 18°C to 25°C; below 15°C, their metabolic activity begins to decline, and at temperatures below 10°C, their activity becomes very weak or even enters a dormant state. Therefore, it is essential to first maintain an appropriate air temperature inside the greenhouse to promote a rise in soil temperature. Typically, daytime air temperatures should be kept between 25°C and 30°C. At night, when greenhouse temperatures drop, to prevent heat loss from the soil and maintain a stable soil temperature, in addition to using plastic mulch, crop residues can also be spread along the cultivation rows.

　　Third is soil pH.

　　Data indicate that a soil pH between 6.5 and 7.5 is optimal for the proliferation of beneficial microorganisms. Vegetable growers can adjust their soil conditions to achieve this pH range, thereby promoting the vigorous growth of these microorganisms. Furthermore, the efficacy of bio‑fertilizers relies on microbial decomposition of organic matter in the soil; if organic amendments are insufficient, the microbes will be unable to release nutrients. Therefore, prior to transplanting vegetables, it is essential to apply an adequate amount of organic fertilizer—typically around 5,000 kilograms per mu.