Sound Advice: Making Dormant Microbes Work for You

How to make the most of your dormant soil microbiome during cold winter months.

Over millions of years, nature has developed a seasonal, cyclical routine that life follows, and growers have learned to align their processes to make the most of what nature provides and when. As we head into winter, that rhythm plays out underground. 

Soil microbes have an important role in soil health, providing nutrients like nitrogen and phosphorus to crops in plant available forms. In exchange, the microbes receive carbohydrates that the plants create through photosynthesis. In the winter, crops no longer need the nutrition the microbes provide and die off, but the microbes don’t. Instead, they go dormant as the temperature drops. 

Like all living things, microbes have optimal growing conditions. For most microbes, activity doubles for every 10°F that the temperature rises, starting with soil temperatures around 60°F until about 85°F when activity levels off. Microbes thrive in warm weather, with the activity of some species continuing to increase over 100°F in some areas.

Where there’s less of a dormancy period, microbes would begin working on applied fertilizer right away, wasting it before spring. In colder climates, however, growers may decide to apply fertilizer in the colder months, allowing it to wait in the soil for future use.

When the first wintery weather systems moved through Minnesota in late November, soil temperatures, which tend to lag slightly behind atmospheric temperatures, fell well below 60°F. The transition from farm season to winter can be very quick. This year harvests ran later than usual, and as combines finished up in the field, the microbes were already headed into their dormant season. 

But while the microbes are dormant, growers are not. In addition to preparing the soil bed and tilling, many growers will apply fertilizer in the fall to save themselves time during the spring planting season. Dormancy is key to off-season fertilizer application; in warmer climates like Florida, where there’s less of a dormancy period, microbes would begin working on the fertilizer right away, wasting it before spring. Where there is microbe dormancy, however, growers may decide to apply fertilizer in the colder months, allowing it to wait in the soil for future use and saving themselves time next year. In years with late harvests like this one, though, some growers may have put off nitrogen application until next year, as there wasn’t much time before winter weather rolled in and shut down operations.

In the spring, the natural rhythm brings back warmer temperatures and right before microbial activity really picks up again, growers plant. Once again, there are some advantages to following this seasonal rhythm:

  • Waiting for the microbes: You don’t want the microbes to be active for too long without a crop in the ground. Crops provide microbes with carbohydrates and sugars they need in exchange for the nitrogen and phosphorus that can be hard for plants to access. Waiting too long to plant deprives the microbes of their food source and risks weakening the crop-microbe symbiosis.
  • Benefitting the crop: Planting too early leaves the crops in the ground without receiving any benefit from the still-dormant soil microbes. By aligning planting with the emergence of microbial activity, new crops can start out strong.

Warmer temperatures are not the only signal that will bring microbes out of dormancy. Because of the special relationship between plants and soil microbes, crops also send out signals to the microbes that it’s time to wake up. That’s how SOURCE® works. It’s applied during key times for nutrient uptake to wake up microbes and unlock more nutrients. And with nitrogen prices still high, some growers may be looking for alternative products, like microbiome activators, to provide nitrogen to crops next year. 

By understanding how nature’s cycles benefit them, growers can work with these natural processes and protect and preserve beneficial systems, like the soil microbiome. These rhythms have existed for millions of years, and many growers are already tuned in to them, letting nature do the work for them.

Photo by Joseph Ngabo.