Comparing Tillage Methods in a Tough Year for Corn and Beans

For the crop producers who were able to prepare their fields and plant this spring, overabundant rain and a wide range of temperatures led to tough choices when it came to seedbed preparation. Anxious to get in the field, they sometimes had no choice but to till and plant into wet soils that then, depending on the region, dried out too quickly or became a cold and inhospitable environment for germinating seeds.

Growers cooperating with the first year of tillage trials for the AGCO Crop Tour and the agronomists at Precision Planting’s PTI farm faced similar challenges as they set out to compare common methods of spring seedbed preparation in side-by-side plots. Research in these Crop Tour corn plots looked at the effect of secondary tillage passes on several benchmarks of seedbed quality and crop success. Meanwhile, the corn and soybean tillage study plots at PTI are a subset of field research conducted in 200 acres of agronomy trials at Pontiac, Illinois.

Surface compaction resulting from use of vertical tillage in wet soil conditions this spring.

While the final results won’t be known until after harvest, early and mid-season observations and data from some of the AGCO Crop Tour plots already provide some insights into tillage methods, as well as how advanced planter technology was able to compensate for the tough conditions, says Jason Lee, North American agronomy and farm solutions specialist for AGCO.

Not surprisingly, he says his biggest observation this spring was that “when soil conditions are wet, it doesn’t really matter what you do for tillage – you’re going to create problems.”

That being said, based on aerial imagery and in-person scouting of plots near El Paso, Illinois, that compared use of a vertical tillage tool vs. a field cultivator, Lee says “the young corn plants in the field cultivator plot looked much more robust than the ones in the vertical tillage plot on that particular farm.” He says he believes the difference is that under the wet conditions, the field cultivator worked the soil deeper, allowing for deeper root development and better access to available nutrients and water. In the other half of the field, the vertical tillage tool worked only a shallow layer of soil and created a compaction layer below, resulting in shallower root development.

“It’s what happens sometimes when shallow tillage is used to just ‘tickle’ the soil, to open it up to get it to dry out,” he says. “All you did was create a lot of hard soil clods in the top inch, and then an inch below, you have a hard, compacted layer. So any time we do tillage, we need to go in when conditions are as fit as possible. This year, that wasn’t always a choice.”

Visual Comparisons: Field Cultivator vs. Vertical Tillage

In the El Paso plots, data collected with SmartFirmer® seed-firmer sensors during planting generated a furrow moisture map that shows a visible difference between the darker green moisture readings in the half of the field where a field cultivator was used compared to the lighter-green (drier) readings in the half tilled with a vertical tillage tool. “This shows how tillage depth can affect soil moisture,” Lee says.

Furrow moisture levels at planting between seedbeds prepared with a field cultivator (top/north half)  vs. a vertical tillage tool (bottom/south half), measured on-the-go with SmartFirmer sensors on the planter. The field was planted on June 8, 2019, near El Paso, Illinois.

The visual differences didn’t stop there. He noted the difference in corn plant height between the two halves of the field himself when he was there on July 15, about the same day the field health images of the plots (below) were captured in Climate FieldView™. The vegetation map on the left is based on satellite imagery to show current vegetative biomass. The image on the right is a field health or scouting map that highlights the variability in vegetation within the field, with the better performing areas in green and lower performing in yellow and red.

On left, vegetative biomass in the El Paso, Illinois, field plots on July 13, 2019. On right, same field, same day, shown in a field health map that contrasts high- and low-performing areas of the field. North half was tilled with field cultivator prior to planting; south half was vertical-tilled.

Crop Residue Management Matters

In the two Wausau plots, one of the data points collected at planting was percentage of residue cover on the soil surface. In side-by-side comparisons of a tillage pass with a Sunflower® 6830 Rotary Finisher with that of a compact disc, the rotary-finisher plots had 7% less residue cover than the compact-disc plots. (See Table 1.) “The rotary finisher did a better job of incorporating surface residue during the tillage pass,” Lee explains.

Table 1. In both of these trials, 7% more residue cover remained on the field surface after a spring tillage pass with the compact disc than did with the rotary finisher. AGCO Crop Tour corn tillage plots, Wausau, Wisconsin, 2019.

Higher residue cover at planting increases the odds that old plant residue will end up in the seed furrow, where it can delay germination and impact corn yield by robbing moisture, causing air pockets and lessening seed-to-soil contact, says Jason Webster, the Precision Planting commercial agronomist who manages the PTI farm. In a seed trench residue management study at PTI in 2018, for every 1% loss in clean furrow, corn yield decreased by 1.1 bushels per acre. (See Table 2.) Using row cleaners on the planter is one way to move excess surface residue out of the row during planting.

Table 2. Manual infestations of corn residue were placed directly on each corn seed in the furrow at percentages from 100% clean to 64% clean furrows. Corn yields ranged from 210 to 240 bu/A, indicating losses up to 30 bu/A as a result of high amounts of residue in the furrow. Losses could be even higher in typical field settings, where residue would likely be distributed throughout the seed furrow rather than just on each seed. PTI, Pontiac, Illinois, 2018.

Strip-till Is An Advantage in Wet Soils

This year, wet soils during spring tillage on the PTI farm made a huge difference in the ongoing tillage trials that Webster conducts to compare yields and economic impacts of conventional tillage, strip-till, vertical tillage and no-till systems in continuous corn and a soybean-after-corn rotation. “By far some of the worst stands we had were in our conventional tillage,” he says.

“We were so wet in early spring that in the conventional tillage plot, we had to come in with a soil finisher and just open it up,” he says. “Then temperatures were 85 to 90 degrees after we worked it, with winds blowing 25 miles an hour. It became super-dry soil on the top 2 inches. So that posed a challenge at planting time, because you really had to have the right down force and correct residue manager settings to achieve the right planting depth. Otherwise you had seed sitting in dry dirt.”

In contrast, “the strip-till plots were probably my best stands in both corn and soybeans this year,” Webster says. “We made some beautiful, wide fall strips back in October when the weather was really good, and it paid off. We didn’t have to work it before we planted.”

Tillage System ROI

In 2018, the ranking of economic returns from the four tillage systems studied at PTI were quite different in corn-on-corn vs. soybean after corn.

In continuous corn, yields varied within only 7.8 bushels per acre between all four tillage programs. Strip-till yields were highest at 192.6 bu/acre. Webster uses the University of Illinois Machinery Cost Estimate summary to calculate the cost of each tillage program, including an $8 burn-down treatment in the reduced-tillage programs (strip, vertical and no-till). He reports that those three systems had similar returns, all within $4.10 per acre of each other.

The wet soil conditions at planting in the Wisconsin Crop Tour plots highlighted how too much downforce (done intentionally in this planting trial) can create sidewall compaction, which often leads to hatchet roots that can reduce yield.

Conventional tillage, however, due to a two-pass system cost and being tied for the lowest overall corn yields in the study, returned $20 per acre less than the highest-returning system (strip-till). Webster posits that extended dry weather in July and August of 2018 may have given the yield advantage to the reduced tillage plots, which likely had lower soil temperatures and preserved more moisture that the conventionally tilled soil.

In the soybean tillage study, yields for all four tillage systems were within 3.2 bu/acre of each other, with conventional and strip-till yielding the highest. When it came to returns, conventional tillage led with $456.52 per acre, followed by strip-till, no-till and vertical tillage a full $18.70 per acre less than conventional. Webster notes that 2018 was the first year PTI planted crops on the farm, and the very low-pH soil in the soybean plots probably benefited somewhat from conventional tillage mixing up the soil more than the reduced-tillage systems.

More Tillage Research Coming from AGCO Crop Tour

The AGCO Crop Tour tillage plots, as well as the ongoing planting technology trials, will be taken to harvest this fall to measure yield differences. The rough spring certainly set up a unique chance observe how methods and plants fare in an abnormal year.

“In relation to plant spacing, even with poor planting conditions this spring, the advanced planter technologies on the White Planters still allowed for uniform plant spacing, even though seedbeds were less than ideal,” in plots across Wisconsin and Illinois, he says. He also credits DeltaForce® automatic down force with being able to plant successfully in cloddy seedbeds that looked pretty bad on planting day.

Lee emphasizes that AGCO is in its first year of studying how secondary tillage affects crop health, and these initial observations from a limited number of locations are not meant as recommendations. “We’re learning a lot, even in a year that’s so abnormal,” he says. “Our goal is to find the best practices over time that give plants their best chance to handle stress and thrive, and it begins with tillage.”