Why what happens beneath the surface after the combine leaves is next year’s biggest opportunity
When the crop is off, the bins are filling, and the combines are being parked for the winter, it’s tempting to think the season is finally over. And while you’ve certainly earned that sigh of relief that comes with grain in the bin, here’s your reminder that the season isn’t quite finished yet, at least not for your soil.
As the dust settles this fall, the biological engine beneath your feet is just getting started. While producers are evaluating yields and delivering contracts, billions of soil microbes are actively cycling nutrients, decomposing residue, building organic matter, and preparing nutrients for next year’s crop. Soil biology doesn’t operate according to the calendar. It operates according to temperature, moisture, oxygen, and food supply.
What happens in your soil between harvest and freeze-up may have a greater impact on next spring’s crop than many of the decisions made after seeding.
This week’s Field Note explores exactly what’s happening below ground and how you can use that opportunity to build yield, soil health and profitability into 2027, starting today.
RESIDUE. NOT TRASH.
Can we stop calling what’s left behind the combine trash and start calling it what it really is: fuel for your soil engine?
Every bushel harvested leaves behind roots, stems, chaff, straw, and other organic compounds. Hidden within that residue is a tremendous reserve of carbon, nitrogen, phosphorus, sulfur, potassium, and dozens of micronutrients. The challenge isn’t that these nutrients are unavailable. It’s that they aren’t available yet.
Turning crop residue into plant-available nutrition requires two critical biological processes: decomposition and mineralization. The speed and efficiency of those processes depend on the health of the soil ecosystem and the microbes that call it home.
Think of residue as a slow-release fertilizer program spread across every acre of your farm.
The microbes determine how quickly that fertility becomes available to next year’s crop.
WHY C:N RATIO MATTERS
One of the biggest factors influencing nutrient cycling after harvest is the carbon-to-nitrogen ratio (C:N ratio) of crop residue. In many ways, a lack of understanding around C:N ratios is probably why residue earned the nickname “trash” in the first place.
Here’s what you need to know.
Microbes require both carbon and nitrogen to grow and reproduce. Carbon is their energy source. Nitrogen is their building material. As a general rule of thumb, net mineralization is more likely to occur when the C:N ratio is balanced at roughly 20:1 or lower.
When residue contains a very high carbon-to-nitrogen ratio, typically 30:1 or higher, as is common with cereal straw, microbes need additional nitrogen to break it down. To find that nitrogen, they temporarily pull plant-available nitrogen from the soil solution and incorporate it into their own biomass. This process is known as immobilization.
This is why producers sometimes observe nitrogen deficiencies in fields carrying heavy cereal residue the following spring. The nitrogen hasn’t disappeared. It’s simply tied up inside the microbial workforce processing that residue.
Historically, many producers dealt with this “trash” by burning it, baling it, or physically removing it from the field. The problem is that those practices often removed valuable carbon and nutrients along with the straw. In many cases, nutrients that were already present in the field had to be replaced later with purchased fertilizer.
High-carbon residue isn’t the problem. A lack of biological capacity to process that residue is the problem.
The goal shouldn’t be to eliminate residue. The goal should be to build a biological system capable of converting that residue into plant-available nutrients as efficiently as possible.
Think of it this way: residue is not waste. Residue is next year’s fertility program waiting for biology to unlock it.
FUNGI VS. BACTERIA: A PRAIRIE STORY
But not all soil biology does the same job.
Bacteria are the sprinters of the soil ecosystem. They rapidly cycle nutrients and break down simple organic compounds. Fungi are the heavy equipment. They specialize in processing tougher materials like straw and crop residue while helping build soil structure, improve water infiltration, and store carbon. Healthy soils need both, but just like the C:N ratio, the balance between the two is an important part of the story.
Before cultivation, Canadian prairie soils were supported by perennial grasses, continuous living roots, and extensive fungal networks. When native prairie was converted to annual cropping, decades of tillage, erosion, and declining organic matter disrupted many of those fungal communities. Bacteria recovered quickly. Fungi often did not. Over time, many agricultural soils shifted from being more fungal-rich to increasingly bacterial-dominated.
This helps explain why some fields seem to process residue effortlessly while others struggle with straw breakdown year after year. It’s also part of the reason newly broken land historically delivered such dramatic yield responses. The biological engine was simply larger, more diverse, and better equipped to cycle nutrients. Like any engine, performance comes down to having the right type and amount of fuel, and the biological workforce needed to process it.
In many ways, regenerative agriculture is about rebuilding that engine. Practices such as reduced tillage, diverse crop rotations, maintaining living roots, increasing organic matter, and supporting soil biology help restore microbial diversity, improve nutrient cycling, and increase the soil’s ability to turn residue into plant-available nutrients.
The goal isn’t necessarily to chase a perfect fungi-to-bacteria ratio. The goal is to build a diverse and active biological community capable of turning residue into next year’s fertility.
THE FALL BIOLOGY WINDOW
Many producers assume biological activity shuts down when the combine is parked for the season, but that’s far from the truth. As long as soils remain warm and moisture is available, the biological engine beneath your feet keeps working. In fact, fall can be one of the most important periods for nutrient cycling, creating one of the most underutilized opportunities on the farm.
The management decisions made between harvest and freeze-up can influence residue breakdown, nutrient availability, soil health, and ultimately how much synthetic fertilizer you’ll need to purchase next spring. Simply put, supporting biology now can help keep more fertilizer dollars in your pocket later.
Johnston’s Regenerative lineup of post-harvest products such as AnneMaxx™ Zyme, AnneMaxx™ HumiGro and AnneMaxx™ Liquid H in conjunction with Annelida’s proprietary wormcastings foundation AnneMaxx™ Advantage (MA1) are designed to support the biological processes involved in residue breakdown, nutrient cycling, and soil function during this critical fall period.
The goal isn’t simply to make residue disappear. The goal is to convert residue into next year’s fertility.
GOOD DECISIONS START WITH GOOD INFORMATION
The challenge is that every field is different. Some fields cycle nutrients efficiently. Others struggle with residue breakdown, nutrient stratification, compaction, salinity, or biological limitations.
That’s why the weeks following harvest are some of the most important times for your Johnston’s Regenerative Agronomist to be in the field with you. Post-harvest soil sampling provides a snapshot of what remains in the soil after crop removal and helps identify opportunities to improve nutrient cycling, residue management, biological activity, and overall soil function. Combined with field observations, harvest results, and yield data, these insights form the foundation of a profitable 2027 management plan.
| READY TO BOOK A FIELD VISIT? Book your fall soil samples today. The best time to build next year’s crop is while this year’s evidence is still in the field. 1-844-324-7778 johnstonsregenerative.com |
