Measuring soil compaction at planting

The question is one AGCO researchers are currently investigating by measuring the impacts, or lack thereof, of the compaction-reducing technology built into Fendt’s new Momentum brand planter – a centre-fill seeding system equipped with weight distribution and tire inflation technology, as well as an in-line wheel design.

Thus far, observations suggest investments in compaction reduction at planting are worth it – though yield data needs to be gathered before more definitive conclusions can be drawn.

Wet soils make spring compaction a larger issue

While the heaviest equipment may not pass through the field until harvest, frequently wetter conditions during planting substantially heighten compaction risk, says Jason Lee, agronomy and farm solutions specialist with AGCO. Combined with the general move towards more-operationally efficient centre-fill seeding systems – which concentrate load weight more than traditional box seeders – the issue of planting-related compaction has become ever more concerning.

“There are known issues with yield reductions in the middle of those planters,” says Lee. “Also let’s not forget the way tires are designed, we have pinch rows. You have tires on both sides of some of the rows and you’ve added that extra weight. We’ve known this is an issue for years.”

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Penetrometer measurements

AGCO’s research project began by taking penetrometer measurements up to two feet (61 centimetres) in three different locations behind a Momentum planter – in rows where the tractor tire drove, rows where both a tractor and planter tire drove, and rows experiencing no tire traffic. This was done with the planter’s compaction-prevention systems engaged, as well as without.

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In one of their first observations, the AGCO agronomists used a soil penetrometer to measure compaction caused by the tractor/planter compared to compaction in areas where the planter did not run. Penetrometers measure resistance in pounds per square inch as the device is slowly pushed into the ground, simulating a root penetrating soil. The more resistance to the penetrometer, the harder it will be for roots to grow and penetrate soil. Readings were collected in five locations in Illinois, Ohio and South Dakota. – Photo: AGCO

Crop height differences concerning

Speaking to Future Farming in July 2020, Lee said initial penetrometer results indicated the planter’s weight distribution, automatic tire pressure, and in-line wheel design all contributed to minimal compaction addition after that already caused by the tractor. Later in August, the company reported findings linking differences in weight and tire pressure to corn height:
“In a plot near Casselton, North Dakota, [researchers] compared two planter tire-pressure inflation rates: 55 psi, similar to the level for road transport, and automated inflation that maintained tire pressure at approximately 17 psi. Measurements were taken of height in the rows on either side of the in-line tandem center transport tires of the Fendt Momentum planter, at low and high tire inflation pressure.”

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Soil penetrometers provide an indication of soil compaction by measuring the resistance of the soil to the probe in pounds per square inch as the probe is slowly pushed into the ground. The plotted points represent the average of 15 readings in each track across plots located at Chillicothe, OH; Gridley and Pontiac, IL; and two plots in Baltic, SD. The tractor-only tire track was made by the inside dual wheel of the tractor, while the tractor-and-planter track was made by the outside tractor dual followed by the in-line tandem center transport wheels of a Fendt Momentum planter. – Source: AGCO

Observations, the report goes on to say, showed a near three-inch height advantage in corn planted with very high flexion (VF) tires auto adjusted to maintain a low psi (approx. 17 psi), as opposed to the same tires kept at a constant 55 psi.

“As the Casselton crop height observation suggests and many additional university studies have shown, tire inflation can make a difference in compaction and resulting plant height,” says the report.

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Is the impact significant enough?

For Alex Barrie, a farmer, soil management engineer, and compaction researcher working with the provincial ministry of agriculture in Ontario, Canada, some of the data presented by AGCO appears overstated – though not necessarily misleading.

Ideally you should measure where you’re going to drive, then after you do the driving

While penetrometers are useful at identifying where compaction is occurring, he adds it only paints a partial picture. Testing the top 14 inches does not account for what may be happening in deeper soil layers, for example. “Ideally you should measure where you’re going to drive, then after you do the driving,” says Barrie.

Variations in soil profile, water filtration levels, and the ability of soil types to handle and recover from compaction are other relevant factors – as are the traffic levels of past seasons.

“I don’t know if I need a lot of data to say compacting your soil is bad. It’s when you start to really pick apart if a tire does better than another. It’s hard to nail down, but the overall message is on point,” he says. “I’d be curious to see what happens a bit deeper. I might suspect there would be a significant compaction in the subsoil in the wheel tracks.”

Crop height not the best way to measure compaction impact?

Barrie also says crop height may not be the best way to measure overall compaction impact, though recognizes the practical difficulties of gathering yield data in such a study. Collecting yield data in very narrow strips within a 30-foot planter swath, for example, is quite tedious.

“Tires can have an impact on emergence, but I’ve kind of chosen to ignore those early spring effects. You still have to drive on the soil at planting. Regardless of the damage done, some will be damaged, and some will not,” he says. “You can still make your yield on short corn.”

Still significant results

Lee reiterates crop height and penetrometer data alone are not sufficient to draw complete profitability conclusions. But results indicating the Momentum planter did not add any additional compaction when it’s Load Logic system was on are still significant.

Obviously the tractor is causing damage. We don’t want the planter to cause any more damage than the tractor

“The best way to do it is take a lot of samples. One way to combat anomalies is to increase the sample size,” he says, adding they always took penetrometer readings between rows and tire tracks at each study area to provide a baseline measurement, and to account for any existing damage from previous years. “Obviously the tractor is causing damage. We don’t want the planter to cause any more damage than the tractor.”

Yield data forthcoming

Yield data is forthcoming, though. Similar to a 2011 Pioneer study comparing compaction and yield, Lee says they will be analyzing plots by separately harvesting each planter path in thirds – that is, a centre section and two wings. Doing so should highlight differences each of the three sections when the Momentum planter’s compaction systems are engaged, as well as differences between control groups.

Lee adds they are also going a step further by harvesting select plots one row at a time. This, he says, should provide very specific information for their overall analysis. While no yield data exists at the time of this writing, Lee says he hopes to begin harvesting within the next few weeks.

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Footprints made by very high flexion planter tires inflated at 55 psi (left) and 15 psi (right). Note the longer footprint at lower inflation pressure covers a larger surface area and lessens pressure applied to the ground. – Photo: AGCO

Combines and grain carts

From Barrie’s perspective, the most significant and severe compaction issues remain tied to the combines and grain carts employed during harvest – but that doesn’t mean steps to limit damage at sowing shouldn’t be taken. Determining the return-on-investment for compaction-mitigating systems, such as tire inflation and weight distribution technology being marketed by Fendt, can be a challenge.

“It’s a good piece of kit because it has everything you might think to put on after the fact, but you’re paying for it,” says Barrie.

Regardless of the costs, though, his experience indicates growers who have adopted compaction mitigation systems see their investment as positive, if not one they should have made earlier.

“There are a couple really obvious [equipment] designs to prevent compaction, but then there’s what is patentable. Some of these things might not be the best way, but the way it’s the way they can produce and sell it. I’m always a little bit hesitant when it comes to manufacturers trying to sell me something,” says Barrie.

Still, he believes the development of compaction technologies by Fendt is something to watch – and another reason why the company appears to be making greater inroads into the North American market.

The more manufacturers get onboard with this tech, the easier it will be for people to adopt it

“The more you get used to a tool the more it feels like a good idea,” Barrie says. “The more manufacturers get onboard with this tech, the easier it will be for people to adopt it.”

Small efforts can have significant impact

While AGCO waits to accrue yield data, Lee also reiterates growers are not completely dependent on new technology to reduce compaction damage. Indeed, he says small efforts in the, field such as controlling traffic, can have a significant impact. “We don’t always have the luxury of these nice long panting windows” he says.

“Think about axel loads, and when its practical, maybe don’t fill the cart or liquid tank so full. We don’t want to sacrifice productivity, but anytime we can reduce weight it can help.”