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Research Shows Compaction Reduces Yields

Heavy tractors, carts, and combines have the potential to create deep, long-term compaction on U.S. fields and to reduce yield potential, according to a 2014 report from Ohio State University.

Andrew Klopfenstein, graduate research associate, and two colleagues in the engineering department presented their preliminary new model for soil compaction at the American Society of Agricultural and Biological Engineers annual conference.

“Machinery just keeps getting bigger,” says Klopfenstein. “Little research is being done on the impact of that equipment on soil tilth, or soil health, or the yield loss for a given crop. Farmers are assuming they can correct 90% of compaction with tillage, but the depth of compaction with some pieces now goes down 2 feet or more.

“You cannot correct that with tillage,” he adds.

In one example, Klopfenstein reports the yield impact for a 2,000-bushel wheeled grain cart with an approximate weight of 30 tons per axle (200,000 pounds gross weight). The grain cart produced compaction to a depth of 34 inches in both normal and wet soil conditions. The traffic pattern covered 29% of the field. From model predictions for normal conditions in the trafficked areas, the yield loss was slightly over 50% for the following crop of corn.

Current model predictions are based mainly on older research, so Klopfenstein recognizes that this number needs to be verified with more research. This has led to the team creating new compaction plots with higher 25- to 40-ton axle loads to collect yield data to create a more accurate yield-loss model.

Updating the model
Much of current thinking about tillage is based on research from 25 to 50 years ago. Early baby boomers were measuring and making recommendations about compaction under 10-ton axle loads.  

“When you have a 10-ton axle load, compaction can be limited to the top 12 inches of soil. That can be corrected,” says Klopfenstein. “Axle loads now are creeping up to 20 and 35 tons. Anything more than 10 tons is causing deep soil compaction, which is much harder to correct.”

In addition to higher axle loads, the new research is also looking at how compaction impacts different soil types. The new master model is continuously changing as more data is collected.

“Before we started our new compaction studies, we ripped our plots as deep as we could to reset the soil. Next, we created trafficking events with heavy grain carts, then we assessed crop vigor with manned remote-sensing overflights,” he says. “Once harvest occurs, we will see just how accurate our original model estimations are. Then, we’ll tweak the model to better fit the given growing season and traffic events.”

Compaction measurements
The team of engineers was startled when they understood the results of their compaction measurements.

“My initial surprise was the depth of influence for high axle loads. Farmers really have no idea, when they have large grain carts and large class 9 or class 10 combines, just how far into the subsoil they’re actually compacting,” he says. “If the soil is wet and you’re running a heavy grain cart across the field, the depth of compaction and the yield loss you’re going to see is significantly greater.”

Under continuous no-till, shallow traffic compaction can correct itself in about five years, assuming there is no additional damage, he says.  Deep subsoil compaction can take up to 10 years to alleviate, if at all.

“When the compaction is severe enough, there is nothing you can do mechanically to correct it,” explains Klopfenstein.

Returning to smaller, lighter machinery isn’t likely to be a practical option, but it has led to other ideas.

“Here at Ohio State, we are looking at the idea of using a fleet of much smaller autonomous vehicles, all below the 10-ton axle load,” he says. “Like a fleet of drones, they could work a field together. Once the axle weight is lower, it doesn’t matter how many are in the fleet; compaction and yield loss will be minimized.”

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