Have you ever heard of the “Seven wonders of the corn yield world” — weather, nitrogen, hybrid, previous crop, plant population, tillage or no-till, and biologicals.

These are the top factors that affect corn yield the most, according to Fred Below, professor of crop sciences at University of Illinois, with weather and nitrogen at the top of the list.  

But what about biologicals? On average, they affect corn yield the least, but when done right, they can have a big impact.

Below and Connor Sible, a Ph.D. candidate at University of Illinois, talked biologicals in corn at this year’s virtual Commodity Classic.

For a field with an average 260-bushel yield, the use of biologicals will account for 10 bushels, a small number compared to weather or nitrogen, each of which account for 70 bushels of that total yield.

But biologicals — plant growth regulators, beneficial microbes and biostimulants — have their own distinct advantages. For one thing, they’re versatile. They can be applied in-furrow, at post or during the reproductive stage as a foliar, and even on crop residue.

"These are already going on with another application process, so this is key, and it is given a free ride,” Below said.

Crop residues, which he calls nature’s biological, build soil organic matter from a previous corn crop or through cover crops, and they prevent soil erosion and provide food to microorganisms.

Below compared two fields for seven years, one with continuous corn and the other with a corn-soybean rotation, to see if there was a yield penalty from continuous corn. There was — 25 bushels by the seventh year, he said, and it usually gets worse with time. Why? The amount of residue that immobilizes nitrogen and other nutrients that aren’t managed properly.

“If you’re in continuous corn, it is all about managing the residue,” he said.

A field with a 177-bushel yield leaves around 4.2 tons of stover per acre. That stover has a lot of nutritional value, Below said — 84 pounds of nitrogen, 17 pounds of phosphorus and 97 pounds of potassium.

It’s also a lot more valuable than a synthetic fertilizer. “The value of a potassium molecule in residue is three times the value as a chemical fertilizer. Same is true of nitrogen and potassium, though at a lesser amount,” he said. “When nutrients are released from residue, they’re not tied up in soil, and that release comes along with biological activity.”

One way to get the full value of these nutrients is by chopping the residue so the soil microorganisms can degrade it, or to treat it with a biological to enhance its breakdown. You can also chop and treat it to get the best of both worlds.

Stress reliever

It’s no secret that growers are producing more bushels per acre than ever before. One key reason, he said, is the growth in plant populations.

In 1960, plant populations averaged 18,000 plants an acre. In 2020, the average was 32,000 plants an acre. The average corn yield increases 2 bushels per acre per year, he said.

Corn yields are the product of plant population, kernels per plant and weight per kernel. The only thing a grower can control is plant population.

So where can a biological fit in? The trade-off to increased plant populations are smaller root systems. Below said that using a plant growth regulator can provide some stress relief and enhance nutrient uptake. But it’s important to get this right.

“The plant response to any legitimate plant growth regulator follows what I call the “Goldilocks Rule.” You have to get it just right to reach optimum level of growth,” he said.

Choosing a biological

Sible describes the world of biologicals as the “Wild West of ag,” since there are so many products out on the market.

Before diving in, though, he suggests making sure the other factors have been addressed. “You got to have those six wonders set, and then biologicals; that’s the next step,” he said. “But it’s really important to know how they work.”

Here are the biological categories and how they work:

Nitrogen fixing bacteria. These increase plant-available nitrogen by taking atmospheric nitrogen and converting it to a form that can be taken up by the plant, converting it to ammonium and then ammonia. Think of something like Pivot Bio’s Proven or Envita.

Phosphorus solubilizing bacteria. These increase the availability of mineral phosphorus in soils. Phosphorus is often bound to cations like aluminum or calcium, and is unusable to the plant. Solubilizing bacteria can make this phosphorus available, freeing it up for plant use. A product like iNvigorate falls under this category.

Mycorrhizal fungi. These help to extend the root system. Seed inoculation is best, he said, as the fungi will grow with the root. The source of the inoculum will affect its efficacy, as well as the soil environment you’re using it in.

Enzymes. These are relatively new. They increase availability of organic phosphorus, which is bound to organic matter. The enzyme grabs the organic matter complex in a plant, taking it apart and making it available for plant uptake.

Keep in mind, though, that not every enzyme works the same, and you’ll likely see variations depending on the field it’s being used in and whether it has a history of manure.

“Variations in soil environment regarding native P levels and soil organic matter concentrations determine what enzymes are best for that field,” he said.

Humic and fulvic acids. These can chelate soil cations and feed soil microbes. Humic acid has higher carbon levels, while fulvic acid has more oxygen.

“And these functional groups help chelate cations, like calcium, aluminum or zinc, which are known to bind with phosphorus. If you can chelate these cations, you can prevent them from interacting with P, keeping the P fertilizers available,” he said. It can also increase zinc uptake for later in the season.

Marine extracts and sugars. These are often tied together. Marine extracts are soil-applied and stimulate microbes and roots; sugars are foliar-applied and mitigate stress, like drought.  

“Biologicals can be effective at increasing crop grain yields, but that efficacy does depend upon the type of biological product your using," he said.