It was at the 2017 National No-Tillage Conference that Marion Calmer began to wonder if stratification was a problem on his no-till farm in Alpha, Ill.

For 30 years, he’s been surface-applying his phosphorus (P) and potassium (K). While his soil tests indicated good levels, he was seeing symptoms of nutrient deficiencies in the corn, such as purple leaves and stunted growth. 

“Even when the corn plant is a foot tall and I get some drier weather, I’m getting burnt leaf edges and poor yields in dry years,” Calmer says. “No-till should really shine in dry years.”

He also noticed that P and K applications often didn’t pay off. For three decades, he’s had 60-foot-wide plots where he would either broadcast P and K, or skip an application on a corn-soybean rotation. He calculated that every dollar’s worth of P and K he spent would only grow back 40 cents worth of grain. 

Spotting Stratification

The first step Calmer took after the 2017 conference was to examine the difference in nutrients vertically throughout his soil tests. He took some soil tests 8 inches deep and separately tested the top 4 inches from the bottom 4 inches. The results showed the top 4 inches had higher nutrient levels than the bottom.

He wondered how serious the vertical stratification was, so he decided to test his soil in 2018 at 0-2 inches, 2-4 inches, 4-6 inches and 6-8 inches deep.

The results showed the top 2 inches of soil had 108 pounds of P, 54% of the P available in the soil.  

“Where do we plant the corn seed?” Calmer asks. “Two inches. If I plant the corn seed at 2 inches, half of my P is above the seed. Do corn roots grow up? No, they grow down.”

At the 2-4 inch and 4-6 inch depths, he tested at 22 pounds of P each. At 6-8 inches, it was 44 pounds.

He saw similar results with his K. The top 2 inches measured in at 428 pounds, 43% of K available. The rate at 2-4 inches was 244 pounds, followed by 172 pounds at 4-6 inches and 152 pounds at 6-8 inches.

These results further confirmed Calmer had a stratification problem and raised more questions. He wondered if the problem was getting worse over time. He took more tests in 2020 and 2021 to compare to the 2018 results.

The data showed the problem was getting worse over time. The top 2 inches of soil had 113 pounds of P in 2020, a 5-pound increase, and 119 pounds of P in 2021, an 11-pound increase compared to 2018.

“As I continue to put P and K on top of the ground, that number in the top 2 inches is getting larger, not smaller,” he says. “If I’m truly stratifying the soil, as plants grow, they’re sucking the nutrients out.”

When he looked at the results from the test at 6-8 inches, Calmer saw the numbers decrease. His rate of P dropped to 43 pounds in 2020 and 42 pounds in 2021, decreases of 1 and 2 pounds compared to 2018. 

Microscopic Measuring

After those results, Calmer was curious as to how much stratification there was by the inch.

“This is a process of evolution,” he says. “I saw a potential problem, decided to go a little closer, and now we’re really looking at it with a microscope. How serious is it?”

On a soil averaging 65 pounds of P per acre, he tested at 142 pounds in the first inch. The measurements indicated 97 pounds of P between 1-2 inches. Then it dropped to 58 pounds in the third inch and continued below 50 pounds for each inch below 4 inches. The 8-inch depth measured the lowest at 37 pounds.

“The average was 65 pounds. I’ve got a whole lot up here at the top, but I’ve got nothing where the roots are growing,” Calmer says. “The roots are our funnel that keeps getting bigger, and the nutrients are our funnel that keeps getting smaller.”

Results for K were similar. On a soil averaging 279 pounds, the highest concentration was in the first inch at 569 pounds. Then the level dropped to 377 in the second inch. The level of K continued falling under 300 pounds at 3 inches and deeper, with the lowest rate of 177 pounds at 8 inches deep.

Tillage Test

After confirming that stratification was occurring, Calmer knew he needed to put his nutrients where the roots would be. He had to flip that highly concentrated soil — and he knew the piece of equipment that would do it.

“I’m here to admit, I did plow a strip 60 feet wide and 1,000 feet long in one of my long-term no-till fields,” he says. 

He assumed that if he could flip that top 8 inches of soil completely upside down, he would invert the funnel of nutrients. After moldboard plowing the plot, he went to the same spots he previously soil tested and took new tests. 

The tests showed that he did move the nutrients down. The top inch previously measured 569 pounds of K. After tillage, it tested at 222 pounds. The second inch was previously at 377 pounds, and it decreased to 253 pounds after tillage. The bulk of K was now in the 3-4 inch depth at 377. K started to drop again after that depth with 8 inches deep still testing at 177 pounds. 

“I was successful at taking the high fertility soil on the top and moving it down, but I only got it into that 3-4 inch area,” Calmer says. “We learned here that wherever you do tillage, we normally only mix the soil about halfway down.”

It’s one reason why the experiment didn’t convince Calmer to give up no-till. He also looked for stratification with his soil organic matter and pH, but he didn’t find any. Vertically throughout the soil profile his organic matter measures around 3.2-3.3%. 

“I assumed that my earthworms were moving P and K vertically in the soil profile,” Calmer says. “I assumed wrong. They move organic matter. Any of the videos you ever see, the earthworm comes up, grabs some residue and takes it down the hole with him. He does not take P.”

Calmer says this means vertical stratification is not a no-till problem — rather it’s a fertilizer management one.

Strip-Till Solutions?

Now Calmer’s goal is figuring out how to get the P and K below the seed.

He’s considering natural ways of moving the nutrients down, such as cover crops, as well as equipment that will place it in the soil, like an Environmental Tillage Systems SoilWarrior strip-till machine. In the 1990s, he strip-tilled his corn and placed the P and K in the strips, and says he was “pretty tickled with it.” But he had to give up strip-till when he moved to 15-inch corn rows.

The next steps in his experiment are analyzing how much additional yield he’s gaining by destratifying the soils. Then he can determine how much money he can invest in new equipment that will place P and K in the root zone. 

Calmer harvested the plots where he moldboard plowed this fall and did see a yield advantage to them, but as of this publication, he had not analyzed how much of a difference it made. His analysis will be revealed at the 2023 National No-Tillage Conference and on his website later this year (see below).

“From a cosmetic point of view, mechanically mixing the nutrients lower down made a heck of a difference,” he says. “The corn just looks a lot better. The initial data shows it yielded better. All indications show that the buildup of nutrients on the surface has no upside for me, my crops or my environment.”