By Connor Lynch
Across Ontario, the bizarre weather, from searing heat to monsoon soakings, has dominated headlines.
But there’s a much more subtle yield-thief at work in fields across the region, one that could be causing long-term corn and soybean yield losses by as much as 20 per cent.
It’s compaction. Agronomist Peter Johnson spoke with growers across the province last month to share what he’s learned about the problem, how bad it is, and how to fix it.
Agronomists always knew compaction was bad, but new technology has made measuring the impact of compaction a lot more clear, and the results are surprising about how bad it is. Surface compaction, only as much as inches deep, can cause yield losses as high as 20 per cent over seven years, and most of it comes in the first year. That surface compaction is almost directly related to tire pressure, Johnson said. The target for farmers? An aggressive 15 psi. For the vast majority of growers, that’s going to mean getting a tire system that lets them change tire pressure on the go, although another way is to just add more tires. But it’s worth it to prevent compaction, he said. Tire pressure could be as much as 90 per cent of your surface compaction problems. Part of the problem is just the size of the equipment. According to OMAFRA, tractors in North America have been getting heavier by an average of 900 lb. per year.
Fortunately, surface compaction is fixable, said Johnson.
Deep compaction has a smaller impact on yields but is basically permanent. A single compaction even 20 inches deep can cause an initial 12 per cent yield loss that, after 12 years, is still causing an annual three per cent yield loss. And that’s just from one, single event. “We don’t do just one event,” he said.
Johnson added that he’s sure there are producers getting close to 20 per cent yield loss from surface compaction in Ontario. Farmers on heavier soils, growing a lot of soybeans and doing conventional tillage without rotating crops, are in the worst situation.
It’s impossible to eliminate compaction, but it can be mitigated. Here are some of the best ways.
• Improving soil organic matter surprisingly helps. The extra material seems to act as a cushion and lets compacted soils open up again, Johnson said. Rule of thumb: For every five per cent clay content in your soil, you should have one per cent organic matter. Odds are, you have about half that. The best way to build it back up? Data from the U.S. suggests a four- or five-crop rotation with cover crops and added organic material, like manure or compost.
• Get a tire system that lets you change tire pressure on the go. It’s probably the easiest way to get your tire pressure down to the magic number, 15 psi, and systems are readily available these days, he said.
• Keep your trips through the field to the minimum. It’s worth it from an agronomics perspective, Johnson said.
• Early-planting dates are always a goal for farmers, but early-season soil tends to be wetter. Wet soil is at much greater risk for compaction, so don’t be too hasty trying to get crop in the ground. Compacted soil could steal the lead you thought you had.
Any compacted fields in Western Ontario are going to be in extra trouble this year, according to research from Purdue University in Indiana, released in June. With the super soaker that hit some areas at the beginning of August, any compacted fields could be facing ponding. Any corn crops getting soaked could start losing nitrogen and be staring down increased disease pressure.