Under Pressure

Wednesday, May 19, 2021

Even if you may not see visual indications, soil compaction could be crushing your crop yield

by Jackie Clark

"In places like western Europe, there are soil compaction maps and national programs. It's really taken very seriously over there," Dr. Dan Reynolds, a soil scientist at Agriculture and Agri-Food Canada based at the Harrow Research and Development Centre, tells Better Farming.

Jake Kraayenbrink has also witnessed this European interest in addressing compaction. He's a farmer in Moorefield and the president of AgriBrink. The company makes systems that adjust tire pressure on the go, allowing farmers to drive with lower tire pressure in the field to reduce compaction of soils.

"We have a dealership now in Europe," he explains. Farmers there have seen the value of the technology. This buy-in may be due to farm size that allows for management on a smaller scale.

"In Europe they sell land by the square metre, and we kind of smile or laugh at that. But they're also very aware of what that square metre cost them," Kraayenbrink adds.

However, awareness and action to combat compaction is building in Ontario, says Reynolds.

"Farm organizations are starting to have field days where experts actually discuss soil compaction, what it is, how to deal with it, how you might try to reduce it. It's all tied up with soil quality and soil health," he explains.

Those educational field days "have had a tremendous impact in bringing these issues to light," Kraayenbrink says. "However, as farmers, we also need to follow through on what we have learned.

"As long as you can make a living doing what you're doing, you don't always feel the need to improve," he says. Innovative solutions to problems like compaction get adopted in hard times.

The slow build of attention to compaction in Ontario may be because the issue "hasn't gotten quite as severe here as it has in western Europe," says Reynolds.

As compaction gets worse, crop rooting depths decrease and soils have less porous space, which may increase fertilizer requirements, decrease soil aeration, reduce crop-available water, and reduce yield, he explains. Those impacts will be the driving force for more farmers to act.

"You get to a tipping point where you see reduced yields and increased input costs. So, that would be the most direct driver that will get farmers to start taking more organized action," Reynolds adds. "Farmers are really quite aware of the issue now, and they are interested in seeing what they can do. It's not just from an economic point of view. That, of course, is important, but they're also interested in environmental quality and soil health."

The compaction impact

"Compaction's an old problem, it's been around for a long time," says Dr. Aaron Daigh. He's an associate professor of soil physics and hydrology in the school of natural resource sciences at North Dakota State University. "What we encounter now has been a slow progression."

Gradually, over time, agricultural equipment has gotten bigger, putting more weight on soil.

"Back in the 1960s, the axle loads on those combines were down around two or three tons. Now we're up around 10 tons," explains Daigh. In the '60s and '70s, "the amount of compaction they had, the winters could pretty much take care of it through freezing and thawing … because the compaction wasn't very deep."

With new, heavier equipment "we can see compaction down to 80 centimetres, getting close to three feet," he adds.

The impact of that compaction is "one of our biggest problems in agriculture without a really great solution," Dr. Adam Gillespie, an assistant professor in the school of environmental sciences at the University of Guelph, says. "What can we do about compaction without having to completely impact your agricultural business model?"

Most farms in Ontario need to use large equipment to operate. However, the resulting compaction is a yield killer, Gillespie adds.

Reynolds agrees.

"Research suggests that somewhere between 60 and 80 per cent of compaction occurs on the first pass," he says. "If you compact the soil, you can expect a 10 to 25 per cent decrease in yield, depending on the soil type, cropping system and weather."

Some researchers are working to measure the impact of compaction more precisely.

North Dakota and Minnesota had wet conditions at both planting and harvesting in 2019 which delayed field activity, and a deep snow layer over the winter prevented the ground from freezing, Daigh explains. He and a colleague at the University of Minnesota conducted "an economic projection of what we expect the regional, two-states consequence to be" in terms of cost of compaction.

"If only 10 per cent of the fields had compaction across the entire two states, which from driving around is probably a low number, over the next two years we project there's going to be half a billion U.S. dollars of economic costs just to the farmers, directly from the compaction," he explains. "That's not including anything we would call an externality."

That half a billion dollars includes the cost of fixing ruts and the yield consequence for the next two growing seasons, he adds. However, additional externalities caused by compaction can include flooding, nutrient loss and increased disease vectors, and impose further costs.

"It almost doesn't even matter what kind of crop type or species that you planted, the percent reduction in yield is going to be quite similar," says Daigh. If you're lucky, yield will only decrease around 15 per cent, but the worst-case scenario can range from 35 to 50 per cent reduction.

Because of the multi-year impact, "there's going to be some land out there, that the farmers don't know what it's like to see the yield when the ground isn't compacted," he adds. By the time the field is starting to recover, it's recompacted.

Some land is likely "consistently compacted and what the producers think that field can produce is probably actually about 20 per cent lower than what it could be," Daigh explains.

Unknown factors

In Ontario, we don't have good data on "what compaction is costing us," says Alex Barrie, an engineer with the environmental management branch at OMAFRA.

Often, compaction has to be really severe to see visual signs, Dr. Ian McDonald tells Better Farming. He's the crop innovations specialist in the agriculture development branch at OMAFRA. "How badly you see compaction depends on the season; the tougher the year, the more it will show up. There's often still a lot of compaction impact that's not visible if growing conditions are excellent after it occurs."

Researchers or government officials haven't conducted any kind of systemic review or inventory of compacted land in the province, Reynolds says. "It's more on an ad-hoc and farm-by-farm basis."

McDonald agrees.

Farmers and experts have anecdotal advice and host demonstration days, he says. But "there isn't a lot of research" on the subject.

"The cause of compaction is simple," he adds. "You put a heavy implement out in the field when it's wet and it sinks in and crushes pore space. But the complexity comes from all the variability across the field, such as topography, soil type and the soil moisture, which can change drastically across that landscape. All of those complicate calculating the true monetary impact of compaction."

The actual parameters to measure compaction also make research difficult, Gillespie says. Bulk density is often a key indicator, and measuring "it is really hard to do properly."

Scientists must extract a tube of soil of a known volume and measure the weight for the calculation.

The challenge is in "the subtlety of making sure you don't accidentally compact your sample. So there's a lot of trouble with trying to actually get that measurement," Gillespie explains.

Not only is compaction challenging to measure, but "the variability means that there's no real value in generalizing," says Barrie.

Nevertheless, some researchers are working on the issue.

"The understanding of soil compaction, how it occurs and what impacts it has, that's fairly understood now. I think the main focus nowadays is how we go about avoiding it or rectifying it," says Reynolds.

Technological approaches

One approach to addressing compaction includes engineering-based solutions, Gillespie says. Those solutions might include tracks, tire innovations and controlled field traffic.

The idea of controlled traffic has "been around for a long time," Daigh explains. The practice hasn't "picked up the full momentum that it could have simply because different pieces of equipment come with different wheel spacing and track spacing. Standardizing that across all tractors and combines and grain carts and wagons and applicators is tough."

However, "more and more people are talking about it," he adds. Farmers are particularly interested in how controlled traffic may work with autonomous equipment.

Other farmers are looking at investing in tire technology.

Producers can avoid soil compaction to some extent by altering tire pressure and the number and width of tires, says Reynolds. "Lower tire pressure, greater number of tires and greater width of tires all reduce compactive pressure on the soil."

Tire pressure must be set higher to drive on the road, but "we only want maybe a quarter or a third of that pressure to not compact out in the field," says Daigh. "Auto-inflation systems for the tires" are getting more affordable.

In Ontario, "it has taken a lot of work just to make the realization that tire pressure has a lot of impact on compaction," Kraayenbrink says. Farmers aren't as familiar with the tire-pressure technology.

"It's new, and it takes a long time to gain credibility," he adds. "The farmers that measure, they're the ones who see the benefit of the technology."

Equipment "has improved significantly over the years and that needs to continue," he explains. "I remember when radial tires came out, we couldn't believe how much money they were."

Farmers with a long-term vision of the impact of compaction on their soils will appreciate the return on investment in tire-pressure technology, Kraayenbrink says. "Until they recognize how much damage there is, it's hard to pay money to change that."

Over the years, many farmers have debated the relative advantages of tires and tracks. In certain conditions, either can perform best, says Barrie.

Though tracks may spread out surface pressure, not much difference exists in overall compaction when you compare dual tires and tracks, especially when you look deeper in the soil, he explains. "Axle weight is approximately the same."

McDonald agrees.

"If there are sloppy conditions and you put the same implement weight across the field as a tire versus a track head-to-head, the track will go through the sloppiness better in most cases, but it's no different in terms of the compaction problem," he explains. "Just because it'll go through the soil, doesn't mean it'll compact less."

For producers keen on reducing compaction, Barrie recommends "buying equipment that has more axles under it," he says. "I would like to see single-axle grain carts go away."

Build stronger soil

One promising note in the fight against compaction is that other soil health enhancement efforts dovetail well with compaction avoidance.

"There is a suite of soil health best management practices that will ultimately increase the strength of the soil, that will allow you some leniency on tire pressure and tire setup," says Barrie.

This approach may not be "as obvious a solution," Gillespie says. But farmers should consider "using the toolbox that soil health offers."

Daigh agrees.

"One of the newer innovative ways to combat compaction is trying to leverage crop diversity out in the field," he explains. By adding diverse forages or cover crops, "you can start creating soil that drains well and is firm and holds up large equipment."

This approach takes a longer-term investment, though it may end up being more sustainable than tillage- based solutions.

"Some farmers will do subsoiling to alleviate soil compaction, but there are both pros and cons to that," says Reynolds. Some cover crops and forage options like alfalfa and various clovers "have deep penetrating roots that can reduce soil compaction over time, although this is usually a multi-year commitment."

Compaction is getting worse, and improving soil health can help that, Kraayenbrink says.

"We're splitting tile so much because soil is getting tighter."

Another key to compaction prevention is patience.

If farmers can wait to drive on the field until "soil conditions are fit, we wouldn't have the problem we have," McDonald says.

However, with many acres, limited labour and variable weather, waiting is not always an option. We, as farmers and ag experts, need to think more about compaction potential as we plan our field operations, he adds.

"Where we're doing a bad job helping folks with that is giving them the toolbox so they can determine whether their soil is fit enough," says Barrie.

Soil experts can work to determine "what constitutes a load-bearing soil and how do you practically determine the relative carrying capacity of your soil."

Agronomic practices that improve your soil structure should increase that capacity, as well as improve drainage to reduce the potential for compaction.

"We can do a lot to improve our soil by how you manage the cropping rotation," Kraayenbrink says. "The healthier your soil is, the more resilient your soil is toward compaction."

A combined soil health and mechanical strategy may be required.

"Absent of that good strong soil, your focus really should be on getting as much rubber and as low a tire pressure as you can get under a piece of equipment after reducing your axle weight as much as possible," says Barrie. BF