Farming is often a race against the clock and Mother Nature, especially when it comes to fieldwork. Whether it is planting, harvesting, or applying manure, these tasks need to be completed in a narrow window, and sometimes, field conditions aren’t ideal. However, if it comes down to harvesting silage at the right moisture or waiting for a field to dry out further to prevent compaction issues, more times than not, a bunker of high-quality feed will win out.
“Compaction is never intended,” said Aaron Daigh, an associate professor at the University of Nebraska-Lincoln. “It is a consequence of farmers being in difficult situations where they need to get out into fields due to logistics, timing of rainfall, and a need to clean out storage. It always happens in the context of difficult decisions that need to be made.”
That being said, a choice that leads to compaction comes with a cost. Compaction has to do with the macropores in the soil, Daigh explained during a Livestock and Poultry Environmental Learning Community webinar. Well-structured soil has a lot of macropores. These large pores are important for soil health because they allow for aeration, water movement, and root growth. These are great benefits to crop production.
With compaction, the soil becomes more dense. Macropores are typically less than 1% of all pores in soil, but those pores contribute up to 70% of water movement and air movement. So, a little bit of compaction and removal of some of those macropores can have a sizable impact, Daigh said.
Daigh shared a cross-sectional image of soil from two fields. One image clearly had fewer macropores, and he explained that this particular field experienced compaction caused by one heavy equipment event . . . that took place 29 years ago!
“Compaction can occur, and it can persist,” he stated.
Bigger and better?
It is often said that bigger is better, but in terms of machinery, a trend toward heavier equipment has had a negative effect on the risk of compaction. “Compaction is different during this day and age compared to decades ago,” he noted. “Bigger has become the norm.”
With larger equipment and heavier wheel loads, compaction goes deeper into the subsoil. The deeper the compaction, the more limited farms become in the tools they can use to mitigate the problem. Daigh said anyone would be hard pressed to find tillage equipment that can go below 20 inches. Compaction is going below what we can even reach, he emphasized.
As soil moisture changes, compaction risk changes. Wetter soils are more prone to compaction, and fields that are at their water holding capacity are at greatest risk.
When fields have ponding, it is easy to recognize that compaction risk would be high. However, as soon as the water disappears, people tend to think it is then okay to proceed with fieldwork.
“In reality, that is probably the most vulnerable conditions for compaction to occur,” Daigh said. As that water drains, particles can slip down into pockets and become compacted. If possible, Daigh recommended giving the field a few more days to dry.
Right after compaction occurs, crop yields can drop 20% to 30%. Productivity can slowly start to improve, but it takes a long time. And years with drought or excessive moisture can exacerbate the effects of compaction, Daigh noted.
Damage down deep
Daigh recommended leveraging natural alleviation mechanisms to make up for compaction damage tillage can’t reach. One method is biodrilling with roots. This means planting certain crops, such as radishes, with roots that can break through compaction layers.
“This is a multiyear effort to break up compaction,” Daigh noted. “Roots have to form new root channels and then need time to rot out to open up for the subsequent cash crop.” It will take several years to start seeing benefits.
Natural cracking of clay soils during mid-summer, when the ground shrinks and swells, can start to break up some compaction. The crack underground is much deeper than the width of the crack at the surface, but one must wait for a drought to come around for the cracks to open and deepen.
Another potential compaction cure is the freeze-thaw cycle, but Daigh said that is more of a misnomer nowadays. Decades ago, when equipment was lighter, the freeze-thaw cycle could break up compaction in the top layer.
For the freeze-thaw cycle to work, it takes many cycles during a winter, perhaps up to two dozen. During harsh winters in colder climates, an area might get that many freeze-thaw cycles in the topsoil. But down deep, where wheel traffic compaction from heavier equipment takes place, this layer freezes and thaws just once.
“You might be waiting a dozen or two dozen years before winter can actually do anything down deep,” Daigh explained. “It is just not effective. Winter freeze and thaw does not take care of subsoil compaction with the size of equipment we have.”
Some may use deep tillage to tackle compaction, but Daigh said it has poor odds of working because modern wheel loads push compaction down deep.
Do what you can
Since compaction is not easily or quickly reversed, avoidance is preferred over relying on alleviation methods that take years to be effective. To minimize risk, he said to keep loads lighter and balanced. He recommended quad-axle manure tankers over those with tandem axles. Adjust the tire pressure accordingly and limit field passes to avoid creating new ruts.
When possible, Daigh advised driving in the same lanes because 70% to 85% of the damage from compaction happens in the first pass, and that damage carries on into future years. Not only does the damage from compaction run deep, but it also lingers long into the future.
As Daigh said, farmers need to make difficult choices, and sometimes, a decision can have benefits and consequences. While all compaction events can’t be avoided, practices that minimize the risk will have short-term and long-term benefits.
This article appeared in the November 2024 issue of Journal of Nutrient Management on pages 14-15. Not a subscriber? Click to get the print magazine.
