While snow begins to fall outside, conventional wisdom suggests the soil’s biological role has ended for the year.
Not so, say Advancing Eco Agriculture (AEA) founder John Kempf and education director David Miller. They say growing — even in climates with a cold winter — is less about seasons and more about keeping the water, nutrient and carbon cycles turning to your advantage.
The evidence shows up in the spring, Kempf says.
“We’ve all observed this extraordinary flush of growth that happens in the spring that can’t really be accounted for just by moisture alone,” he says. “For alfalfa production, for example, we see this tremendous flush of growth where the first cutting of alfalfa in the spring can be 50-70% bigger than cuttings later on in the year. And this is true even for irrigated alfalfa, so it’s not a question of water supply, but there’s something else going on that is giving plants this flush.
“Why is that? And where is it coming from? It’s coming from accumulated plant-available nutrients, very absorbable nutrients in a biological form that have been released from biology throughout the entire dormant period.”
Taking steps to maximize soil health in the fall can yield results throughout the subsequent growing season, Kempf says.
Soil biology “dramatically slows down, but it still keeps going, solubilizing nutrients and making them available to plants,” he says. “And then the next spring, we see this flush of growth from these bioavailable nutrients that occurred during the dormant period. What we’ve learned is that it’s possible to enhance that biological cycle through the dormant period so that we have enough nutrients not just to last for 30 or 60 days in the spring, but throughout the entire growing season. It’s possible to supply a lot of crops’ nutritional requirements later on during the grain fill period when we really care for that biology in the fall.”
Mineral nutrients of all sorts work together like parts to a car engine, Miller says. Each nutrient plays a role in a biological or physiological process for both plants and bacteria.
“If you don’t have the key to start that engine, there won’t be any power, and the value of that engine is a lot less than it would be if you had a key to start the engine,” he says. “It's the same way when we have a plant that has deficiencies of certain micronutrients or even macronutrients throughout the season. The reason that you have lower yields on your second, third and fourth cutting of forage is largely because there are not enough nutrients to keep that biological cascade going throughout the season.”
Instead of focusing on a soil test to drive starter programs, as well as rates placement on timing, a systemic focus is required, Miller says. The three broadly manageable parts of the cash crop system are soil, plants and the no-tiller.
The soil is made up of textural components like sand, silt and clay; soil life like bacteria, fungi and worms; and mineral components like nitrogen (N), potassium (K) and phosphorus (P).
“You need to be able to evaluate what your soil is and what your system is lacking so that you can properly address that with the best cultural practices,” Miller says. “We need to understand our scenario and situation.”
Soil samples alone tend to focus on the mineral components, including secondary macronutrients like sulfur, calcium, magnesium and sodium, and micronutrients like manganese. That can neglect other critical components of the system.
“One soil sample is not giving us the whole picture of what’s really happening out there in the soil,” Miller says. “It doesn’t guide us correctly. It’s not a sufficient source of information to help us manage our overall nutrition program.”
Using soluble soil testing (saturated paste) figures can drop below what standard testing reveals. A total mineral extraction can show higher levels of some nutrients, though those resources might not be available for plants.
Relying exclusively on results from any of the three tests can result in recommendations for — at best — unnecessary and expensive nutrient applications. In the worst case, excess nutrients could harm crops.
“Let’s say we want to grow a 300-bushel corn crop, and we put out 300-350 pounds of N, and we already have 2,800 pounds out there,” he says. “All we’re really doing is shutting down the N-fixing bacteria and the whole system that’s able to fix N from the atmosphere that’s able to convert the organic matter and utilize the organic matter and release N from last year’s crop.”
Instead of looking at indices for particular nutrients, context is crucial.
“When you a functioning biological system, then you will have more nutrients cycling,” Miller says.
Cycling is important to — among other things — manage crop residue. A 155 bushel per acre corn crop will yield about 45 pounds N per acre, 15 pounds of P pentoxide per acre, 92 pounds of K oxide, 6 pounds of sulfur and 18 pounds each of calcium and magnesium.
“I’ve seen crop residue when they were planting corn after planting beans, and there was still a good amount of crop residue on top of the soil,” Miller says. “Why is that? If that’s happening on your operation, that’s an indication that your biology is not decomposing that crop residue. If you are growing 300-bushel corn, then crop residue management is a real thing. If you are no-tilling into that, and you have a lot of residue that is not decomposed, or at least partially decomposed, it can be a nightmare that starts stacking up.”
Using microbial products to break down corn stalks has shown promise in the past, Miller says.
“Wherever the biology applied, it was way more decomposed,” he says.
Less decomposed residue means less robust biology.
“So when does crop season really start?” he says. “Many people say ‘When I plant the seeds’ or ‘In spring.’ But I think it starts right now, in the fall.”
Managing nutrients thus becomes less about innings and more about keeping the nutrient, water and carbon cycles moving, Miller says.
“It needs to be like breathing,” he says. “It needs to be happening all the time."
The first step should be examining the limiting factors for growth, Miller says.
“Is it tillage?” Miller says. “Is it bare soil? Is it compaction? Is it carbon? What is the limiting factor on your operation? It’s going to be different for different operations and different people.”
To understand the limiting factor, combining soil analyses together to get a complete picture is essential.
“Just looking at one soil analysis that just has NPK — and I get these all the time with new growers that we start working with — is not enough information,” he says. “I cannot make a recommendation based on how much P and K is in the soil because it does not give me any clue what the health of the biology is or what the total mineral pool is.”
Plants can communicate with microbes to reposition nutrients to their advantage, Miller says.
“Let the biology do the work,” he says. “Plant a cover crop. That’s the other thing that’s so important in the fall. You have all of these minerals that are in your crop residue. You have all of these root exudates. You have all of this cycle. And if the soil’s bare from harvest until next planting, a lot of that can be oxidized.”
Seed treatments, mulching and livestock integration can also help. Avoiding insecticides, fungicides, and herbicides can, too. The aim should be to focus on improvement, rather than accomplishment, Miller says.
“A lot of us, and I will include myself in this, would like to think that we have better biology in our soils than we really do,” he says. “There’s always more to do.”