In this month’s edition of Your No-Till History, we’re taking a look at 50 years of research data from the Belleville Research Center at Southern Illinois University, located in Belleville, Ill.

As a graduate student, Amanda Weidhuner, under the supervision of assistant professor Amir Sadeghpour, received a Sustainable Agriculture Research and Education (SARE) grant to sift through 5 decades of data from a long-term fertility trial to determine how tillage intensity affects yields and soil health. 

The Belleville Research Center started researching no-till in 1970 on the site’s Bethalto silt loam soils. The fields were under continuous corn production from 1970-90. They switched to a corn-soybean rotation in 1991. 

The researchers conducted fertility trials on plots with four tillage intensities: moldboard plowing, alternate tillage consisting of 2 years of no-till and 1 year of moldboard plowing, spring discing followed by a chisel point cultivator at 6-8 inches deep, and continuous no-till. The fertility trials on each plot compared broadcasting 175 pounds of nitrogen (N) only; a broadcast application of N, phosphorus (P) in the form of P2O5 and potassium (K) in the form of K2O at 175-80-180; and a control with no fertilization. The fertilizer applications were made during corn years.

“N is broadcast after all the tillage treatments are done, and it’s urease inhibitor treated,” Sadeghpour says, as the researchers didn’t want a bias in the data from potential ammonia volatilization.

Yield Benefit

Corn yields increased across all tillage types after 1990 due to better genetics and adding soybeans to the rotation, according to the Belleville data. In the historical yield data from 1970-2012, Sadeghpour notes a considerable yield gap when applying N only vs. applying N, P and K. He says this shows P and K play a role in production.

The data also shows a yield advantage with tillage in the control plots without any applied fertilizer. 

“We think tillage forces soil organic matter to release some nutrients that would compensate for that,” Sadeghpour says. “No-till doesn’t — or at least doesn’t do it on time.”

The same holds true for soybeans. Sadeghpour says the yield gaps are a lot smaller in plots with tillage, as P and K appear to be limited when fertility isn’t applied to no-till plots.

“Bear in mind that we didn’t apply anything in the soybeans,” Sadeghpour says. “Whatever’s coming is from the corn residual. Anytime you applied NPK, whether it was in corn or whatever was in soybean, no-till was competitive back then and is still now.”

In the 2010s, the 3-year average of no-till corn yields from the plots that received N, P and K was around 225 bushels per acre (see graph above).

“No-till is almost competitive, and even higher than chisel disc, which is now a typical practice, in 2 of the years,” Sadeghpour says. “In 2018, no-till and chisel plow were statistically similar with no-till not yielding as much.”

In the alternating soybean years, no-till averaged about 60 bushels per acre, on par with the varying intensities of tillage.

“Historically what we saw is that as long as NPK was applied, no-till was competitive compared to other tillage systems,” Sadeghpour says. “In recent data, you don’t see much of an increase overall in the corn years, but in the soybean years you see it. The benefits are there overall but usually show up in the soybean years.”

Chemical Changes

No-till outperformed the varying tillage methods in all the chemical soil measurements over the last 50 years, according to Weidhuner.

In the first 20 years of research, while the plots were in continuous corn, no-till built up soil organic matter faster than the other plots, adding 0.5% organic matter over the course of 20 years. 

“Organic matter remained high almost every year that we measured,” Sadeghpour says. “One thing that’s interesting is anytime we did 2 years of no-till and then moldboard plowed it, we never gave that no-till time to build soil organic matter. The alternate tillage treatment is not building soil organic matter because you just rip it off basically.”

The researchers evaluated the size of soil aggregates, the particles of sand, silt and clay held together by organic matter, fungal particulates and other things. Weidhuner says larger aggregates are optimal, and surprisingly, moldboard plowing and no-till had roughly the same percentage of large aggregates. 

“We scratched our heads and thought, ‘This can’t be right,’” Weidhuner says. “We ran reps until I couldn’t shake soil anymore, and we’re like, ‘No, that is correct. That is absolutely correct.’ But then we took those large aggregates and looked to see whether they were water stable.”

That’s where no-till came out on top. Weidhuner says no-till’s large aggregates stayed together, while the moldboard plow’s large aggregates fell apart. The more intense the tillage method, the more dissolution of aggregates in water.

Within the aggregates, no-till outperformed the tillage methods in associated carbon and N, which are the amounts stored in the aggregate. Weidhuner says the researchers thought associated carbon and N levels would decrease as tillage intensity increased, but that wasn’t the case for the fields that alternated between 2 years of no-till and 1 year of moldboard plowing.

“The dramatic tillage event actually reduced this plot’s performance as low as the moldboard plow, if not lower, in carbon storage and N storage within those aggregates,” Weidhuner says. 

In fact, Weidhuner says using any form of alternate tillage will cause the soil to lose most of the physical benefits of no-till. At the same time, no-till on its own isn’t enough to significantly build carbon and bring benefits deeper in the soil profile. 

“If your goal is to build soil organic matter, you need cover crops and other practices that go with them to help build carbon and soil organic matter beyond just 0-2 inches,” Sadeghpour says. 

Biological Changes

The researchers also measured how varying levels of tillage intensity affected soil biology over 50 years, starting with earthworm populations. 

Weidhuner says the no-till plot had double the amount of earthworms compared to the plots with annual tillage. The no-till earthworms also weighed more.

The researchers also divided earthworms into three ecotypes. Epigeic worms feed on organic matter in the upper system of the soil, endogeic worms move constantly within the soil without coming to the surface, and anecic worms form burrows 5-6 feet under the surface and create channels as they move between the surface for food and their burrow.

Weidhuner says there aren’t many endogeic worms statistically, so there wasn’t a significant difference among the research plots.

“If we look at our epigeic, these are our composting earthworms, they followed a perfect pattern with the intensity of tillage, so no-till outperformed,” Weidhuner says. “But no-till actually had the least amount of endogeic earthworms because we are looking at the percentage of earthworms.”

Weidhuner also counted and categorized nematodes found in each plot, not all of which will prey on crop roots.

“Some plant-parasitic nematodes are OK, but too many can be detrimental,” Weidhuner says. “There’s actually quite a few plant-parasitic nematodes that we don’t really talk about because they don't cause economic issues. But if you have a lot of ones that don’t cause economic issues, they may start to cause some economic issues.”

A high ratio of plant-parasitic nematodes was associated with moldboard plowing, according to Weidhuner. 

Stable systems provide the right conditions for a variety of nematodes, which are associated with better Haney soil test results and higher organic matter, soil respiration and water-extracted organic carbon. Weidhuner says no-till created the healthiest system for diverse nematode populations.

“There was a stable soil system that developed, and it had this lack of boom and bust that would happen with tillage,” Weidhuner says. “It means all the decomposition happens at once, and then there’s nothing. It’s a very volatile ecological system.”