Soil density plays a key role in corn yields - and profits

A comprehensive five-year FARM JOURNAL project shows that creating and maintaining uniform soil density can spike corn profits by up to $44/acre.

"The benefit from uniform soil density is stronger than we anticipated," says Jess Lowenberg-DeBoer, Purdue University economist, who performed the statistical analysis on FARM JOURNAL'S data. "Depending on the soil type, we saw anywhere from a $1/acre to a $28/acre advantage to uniform density across the corn-soybean rotation. Heavy, silty clay loam soils showed the strongest response and the light silt loam upland fields showed the smallest." 

By executing a few management changes, shuffling equipment and practicing patience when it comes time to go to the field, we were able to dig out a handsome return for our efforts to create and maintain uniform soil density. 

Our tests compared two farming systems at McLaughlin-Dooley Farms, Leroy, Ill. Partners Cole Dooley and Mike and Steve McLaughlin, and employee Derek Strunk performed the fieldwork and weathered the learning curve.

The six project fields covered about 500 acres in a corn-soybean rotation and several soil types. All fields included light silt loam, silt loam and silty clay loam. Two fields were predominantly light silt loams (upland fields) and four were largely silty clay loam (lowland fields). 

Each field was divided down the center. On one side, McLaughlin-Dooley used a system typical on many Midwestern farms, making one pass with a field cultivator and planting corn into soybean stubble. They fall chiseled cornstalks, made a pass or two in the spring and planted soybeans. 

On the other side of each field, FARM JOURNAL field agronomist Ken Ferrie employed a systems approach focused on maintaining uniform soil density and creating an optimum root environment. He watched how each decision and operation impacted the soil. McLaughlin-Dooley performed the work at Ferrie's direction.

Our goal was to evaluate the economics of creating and maintaining uniform soil density, and uncover the best practices for doing so. Several components played key roles, including flotation provided by tracked equipment, types of tillage, and the timing of tillage and other fieldwork. 

"The project was designed to show how the entire package-as well as having all agronomic fundamentals in place-influences yields rather than how much each individual component impacts them," says Ferrie. 

Lowenberg-DeBoer and assistant Rodolfo Bongiovanni used spatial regression statistical analysis to crunch data FARM JOURNAL gathered over five years. The results carry a statistically significant confidence rating of 95%, meaning the same result can be expected 9.5 times out of 10 in similar conditions. 

While the results were strong in corn, soybean yields barely moved. "There was some indication of a soybean response in heavier soils, but overall there was very little response to maintaining uniform density for soybeans," says Lowenberg-DeBoer

Project Prospectus Title: FARM JOURNAL'S Uniform Soil Density Field Test  Location: Leroy, Ill.  Goal: To evaluate the economics of creating and maintaining uniform soil density, and to uncover the best production practices for doing so.  Start Date: October 1995  Final Data Collection Date: October 2000  Time Invested: 4,640 man hours

What we did. Great care was taken to make certain the data gathered during our soil density field test was objective, accurate and real world. Ferrie developed the protocol, and closely supervised the plots along with his staff at Crop-Tech Consulting. Protocol for the project included: 

. Choosing fields with equal yield potential on both sides. 

. Eliminating yield-limiting factors such as fertility. Each field was soil tested, checked for soybean cyst nematode and mapped with a Global Positioning System. 

. Determining soil density conditions by digging pits on both sides of the fields at the beginning of the project. All the fields had compaction at the 9" to 13" depth as a primary soil-density problem.

. Deep ripping both sides of all fields at the start of the project to eliminate existing soil-density problems and create uniform density. Soybean stubble was ripped twice, from two directions. Cornstalks were ripped once and then combination chiseled from the opposite direction.

. Making post herbicide and fertility programs the same for both sides of the fields. Both were scouted for corn borer and disease, and treated equally. 

. Using two near-identical sets of equipment to plant and harvest, with a chief difference-flotation. When possible, equipment on the soil density side employed rubber tracks, while machinery on the McLaughlin-Dooley side rode on tires. 

. Evaluating the plots throughout the growing season and comparing yields by soil type. 

. Extracting data from field maps by soil type and treatment. John McGuire at Spatial Ag Systems, Sherwood, Ohio, spent countless hours making sure the data was "clean," accurate and ready to be analyzed.

What we changed. "The way we stepped into different management practices mirrors the way it could be done," says Ferrie. "Much of it is one step at a time, with each step building on the other and taking yields higher." 

Throughout the project, the McLaughlin-Dooley side of the fields stayed the course, with no significant management changes. On the uniform density side, the following changes were made: 

. Tracked tractors, combine and grain cart provided maximum flotation for minimum soil impact. 

. An in-line ripper was used for fall tillage. The operation, which leaves residue on top, was performed in bean stubble rather than cornstalks. (This may not be enough tillage in a continuous corn rotation). 

. In spring, a rotary chopper harrow replaced the field cultivator. 

. The corn planter was outfitted with coultertine attachments and heavier down-pressure springs to handle extra residue and firmer soil conditions. 

. Beans were no-tilled into cornstalks with a no-till drill. 
 

Soil Density Firsthand Mike McLaughlin shares what it is like to participate in our field test:  Being involved in this project certainly reinforced the concept that the learning process never stops. We learned a lot - and are still learning. The entire experience made us more receptive to change and constructive criticism and more likely to question why we do things the way we do them.  Ken Ferrie showed us how important it is to pay attention to details. That includes things like scouting for bugs and diseases, going through the planter or selecting hybrids. Not all of the answers are clear-cut or the results guaranteed, but details count for big differences in yield.    McLaughlin-Dooley Farms devoted more than 1,500 hours to this project. Mike McLaughlin, on the tire, shares insights from the group. Others pictured are (left to right) Cole Dooley, Ken Ferrie, Rip Estes, Don Rouse, Derek Strunk and John Stein.  The project is over, but we'll continue trying to manage soil density - a never-ending process. We'll continue to deep rip some of our soybean stubble every year and plant corn behind a chopper harrow. We'll also keep working on no-till beans. One of the biggest challenges we have is managing heavy residue. I still fight with planter settings in heavy trash conditions. Sometimes I get it right and sometimes not, but it's worth the fight.  Running tracked equipment has been a great experience. It's hard to put a dollar benefit on some of the intangibles, but we sure feel better using them - especially under heavy loads. In general, working with the machinery companies and their sales people left us with a greater appreciation of the effort it takes to bring new equipment to market. It's expensive and time-consuming.  I'd be a liar to say this study was all peaches and cream. We had our ups and downs. Overall, though, it was a positive experience that allowed us to learn a lot and meet many good people who will be friends in the years ahead.

What we learned. The project data proves that high clay content soils don't like horizontal tillage. At the same time, lighter more coarse soils with less clay content aren't as affected. Horizontal tillage, normally with a field cultivator, soil finisher or disk, creates lose soil on top with a firm shelf below.

"You can rip a field and have the density uniform, then use horizontal tillage and put in a layer that sidetracks roots and undermines the crop's yield potential," says Ferrie.

Density changes from a field cultivator can cause roots to turn-even though the change isn't true compaction or something you can feel with a penetrometer. 

Several new-style aggressive tillage tools level fields in the spring without horizontal tillage. We used McFarlane Manufacturing's Spiral Reel Stalk Chopper in the soil density trials, but Phillips, Phoenix and Precision Planting also make new-style tools.

What we changed. "The way we stepped into different management practices mirrors the way it could be done," says Ferrie. "Much of it is one step at a time, with each step building on the other and taking yields higher." 

Throughout the project, the McLaughlin-Dooley side of the fields stayed the course, with no significant management changes. On the uniform density side, the following changes were made: 

. Tracked tractors, combine and grain cart provided maximum flotation for minimum soil impact. 

. An in-line ripper was used for fall tillage. The operation, which leaves residue on top, was performed in bean stubble rather than cornstalks. (This may not be enough tillage in a continuous corn rotation). 

. In spring, a rotary chopper harrow replaced the field cultivator. 

. The corn planter was outfitted with coultertine attachments and heavier down-pressure springs to handle extra residue and firmer soil conditions. 

. Beans were no-tilled into cornstalks with a no-till drill. 
 

Soil Density Firsthand Mike McLaughlin shares what it is like to participate in our field test:  Being involved in this project certainly reinforced the concept that the learning process never stops. We learned a lot - and are still learning. The entire experience made us more receptive to change and constructive criticism and more likely to question why we do things the way we do them.  Ken Ferrie showed us how important it is to pay attention to details. That includes things like scouting for bugs and diseases, going through the planter or selecting hybrids. Not all of the answers are clear-cut or the results guaranteed, but details count for big differences in yield.    McLaughlin-Dooley Farms devoted more than 1,500 hours to this project. Mike McLaughlin, on the tire, shares insights from the group. Others pictured are (left to right) Cole Dooley, Ken Ferrie, Rip Estes, Don Rouse, Derek Strunk and John Stein.  The project is over, but we'll continue trying to manage soil density - a never-ending process. We'll continue to deep rip some of our soybean stubble every year and plant corn behind a chopper harrow. We'll also keep working on no-till beans. One of the biggest challenges we have is managing heavy residue. I still fight with planter settings in heavy trash conditions. Sometimes I get it right and sometimes not, but it's worth the fight.  Running tracked equipment has been a great experience. It's hard to put a dollar benefit on some of the intangibles, but we sure feel better using them - especially under heavy loads. In general, working with the machinery companies and their sales people left us with a greater appreciation of the effort it takes to bring new equipment to market. It's expensive and time-consuming.  I'd be a liar to say this study was all peaches and cream. We had our ups and downs. Overall, though, it was a positive experience that allowed us to learn a lot and meet many good people who will be friends in the years ahead.

What we learned. The project data proves that high clay content soils don't like horizontal tillage. At the same time, lighter more coarse soils with less clay content aren't as affected. Horizontal tillage, normally with a field cultivator, soil finisher or disk, creates lose soil on top with a firm shelf below.

"You can rip a field and have the density uniform, then use horizontal tillage and put in a layer that sidetracks roots and undermines the crop's yield potential," says Ferrie.

Density changes from a field cultivator can cause roots to turn-even though the change isn't true compaction or something you can feel with a penetrometer. 

Several new-style aggressive tillage tools level fields in the spring without horizontal tillage. We used McFarlane Manufacturing's Spiral Reel Stalk Chopper in the soil density trials, but Phillips, Phoenix and Precision Planting also make new-style tools. In a separate FARM JOURNAL test plot, the McFarlane Spiral Reel Stalk Chopper and the Phillips Rotary Harrow posted an average yield boost of up to 7 bu. per acre compared with a field cultivator when run in the spring over ground ripped in the fall. 

"I can't emphasize enough that density changes in the top 4" of soil play a big role in [corn] yields," says Ferrie. "The more shallow the density change, the more dangerous it is. 

"We never had a drought throughout the five years of the project, and we never had a day when the corn rolled due to lack of water," Ferrie adds. "Even then, we saw dramatic yield swings. The yield differences were in response to conditions in the early growing season. Shallow horizontal layers [on the McLaughlin-Dooley side] created waterlogged soils with as little as a 1" rain."

A wholesale change in equipment or practices is not required to establish and maintain uniform soil density. In many ways, the system captures the benefits of no-till, strip-till and conventional till. Here's what you get: 

. Soils that struggle with drainage can be tilled, yet maintain a high percentage of residue cover. 

. Improved water infiltration and drainage (much like no-till). 

. Quicker soil warm-up and earlier planting. 

. Timeliness advantages gained with tracked equipment and reshuffling field operations. 

. Ground can be ripped after soybean harvest without worrying about soil temperatures as with strip-till. And the grain cart operator needed in corn can do the ripping. 

. Works well in areas where fall nitrogen application isn't possible due to water quality issues. 

However, the benefits come with downsides. You have to handle the extra residue, manage the insects, weeds and seedbed conditions (which mimic those in no-till fields), and balance extra equipment costs with yield gains. 

To create a uniform soil density on your own farm, go to fields with the heaviest soils and most dramatic yield swings. Dig a pit (3'x2' minimum). Check for soil density problems and the depth of the A horizon, which is the first one. Rip the field below the problems or the horizon, whichever is deeper.

As you rip, remember that ripping isn't enough in heavy clay loam soils. You have to break the horizontal tillage cycle to take advantage of the uniformity created by the ripping. Breaking the cycle pays. FJ
 

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