The Cost Of Compaction

Matt Price wants to know why one field on his south central Alberta farm has an average Hard Red Spring Wheat yield of about 68 bushels per acre, while a field across the road, with the same soil and same fertility, has an average of 78 bushels per acre. Is the 10-bushel yield difference related to soil compaction?

To find out, Price subsoiled about 400 acres of his 3,800-acre Acme-area farm in the fall of 2008. He rented an Agrowplow deep tillage tool from two area crop consultants. The tool is 20-feet wide with 19 shanks on 13-inch row spacing. Shanks work as deep as 18 inches.

Price pulled the Agrowplow with his own John Deere 375-horsepower tractor, covering about six to eight acres per hour. The machine rents for $20 per hour and figuring in his tractor, fuel and labour costs, he estimates the whole treatment is costing him about $40 to $45 per hour (or $6 to $7 per acre).

“The thinking is that if compaction is the issue, the subsoiling is something we only have to do every four to six years,” says Price. “So you can spread your costs out over several years.” The Prices operate a continuous cropping, zero till production system. One feature of the Agrowplow tool that appealed to them was its low disturbance. The narrow, one-inch opener and shank can penetrate the ground, work down into the soil 12 inches deep or more as needed, and still leave much of the crop stubble and residue intact, and with no soil inversion — no soil mixing.

Working with his crop consultant Kelly Boles of Center Field Solutions, based in nearby Three Hills, Price chose this field because of their farming practices and field history. The Prices operate a diversified livestock operation, producing beef cattle, hogs and lambs.

“Because of its proximity to the hog operation, this field has received a lot of field traffic for manure application, silage production and grain production,” says Boles. “It was a good candidate to determine if soil compaction was affecting productivity. On one hand, it was still a fairly productive field, but it wasn’t as productive as other nearby fields. Why is that? We’ll see if the subsoiling treatment makes the difference.”

Boles and crop consulting colleague Matt Gosling, of Premium Ag Services Ltd. of nearby Strathmore, went together and bought the Agrowplow subsoiler this fall to be rented out to their clients and others. They are involved in what might be described as a large scale, field research project to determine if soil compaction is one of the overlooked and limiting factors of crop production. As more farmers get involved in precision agriculture, fine tuning and micro-man-

aging fields and soils is becoming more important. Despite all good efforts above ground to use zone soil testing, satellite imagery, infrared technology, variable rate fertilizer application, global positioning systems and auto steer technology to be as efficient as possible, if crop roots can’t get down due to soil compaction, yields may be compromised.

“Our plan is to treat about 2,000 acres with subsoiling this fall and monitor those acres to see what difference it makes,” says Boles. Working with several farm clients, the Agrowplow tool has been used on 40-, 80-, and 160-acre (and larger) parcels, to provide side-by-side comparisons of crop production on treated and untreated soils.

“Compaction can be an issue on soils in semi-arid regions (average between 12 to 14 inches of rainfall per season),” says Boles. “Not every acre on every farm needs to be treated, but you have to consider factors such as soil type, field history as far as truck traffic for silage, harvesting, and manure application, as well as industrial traffic related to oil and gas activity on a field. All of these activities can contribute to compaction. We used to think that frost action in the soil would take care of compaction, but that is a long term proposition.” Research has shown, too, that the freeze-thaw cycle has the most impact on compaction in the top two to five inches of soil.

SOLONETZIC SOILS PRONE TO COMPACTION

Solonetzic soils, often called burnout or gumbo soils, are prone to compaction. Alberta alone has an estimated 11 million acres of solonetzic soils, which are characterized by a tough, impermeable hardpan that may vary from five to 30 cm (two to 12 inches) or more below the surface, according to an Alberta Agriculture fact sheet. “This hardpan severely restricts root and water penetration of the subsoil,” says the fact sheet. “Variation in the hardpan causes crops to have a wavy growth pattern during periodsof moisture stress. Deep plowng and, more recently, subsoilng have been developed as methods for improving some of these soils. “

Aside from the solonetzic soils, it appears soil compaction can be an issue on other soil types, depending on field history and activity. Research at Ohio State University showed that 80 per cent of soil compaction was caused by wheeled traffic in just one pass. “The soil can look good on the surface, but get down 10 to 12 inches and you find this layer of hardpan that stops the roots,” says Dennis Laughton, a consulting agronomist based in Calgary. He uses a hand held tool known as a penetrometer to measure soil compaction. As the probe is slowly pushed into the soil it measures the amount of force required to get the tip to go deeper. “Again, research has shown that root penetration through the soil decreases as compaction increases,” he says. “At 300 psi, most root growth stops. On some sites, I’m seeing 500, 600 to 700 psi at the hard pan level and there is no way the roots can growth through that layer.”

Boles says there is still a lot to be learned about the prevalence and impact of soil compaction. “My observation is that the soil will respond positively to the treatment, it is just a question of when and under what conditions will it translate the most to the growing crop,” he says. “With subsoiling, we are changing the equilibrium quite quickly. We may not see the largest benefit to the crop and returns until year two after the treatment. We might need year one to absorb the change.”

For more information on Boles’ subsoiling project contact him at 403-443-0608 or by email at [email protected]He plans to have more details on the project on his website www.centerfieldsolutions.ca.For more on Agrowplow, visit the website at www.agrowplow.com.

Lee Hart is field editor of Grainews, based in Calgary. Contact him at 403-592-1964 or by email at [email protected]

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Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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