It can be called “fractal hierarchical aggregation” or just “fractal aggregation.” Whatever the moniker, the new method of soil health testing promises to offer an important way to assess soil quality and land stewardship, says Guillermo Hernandez, an assistant professor at the University of Alberta.
Hernandez is the lead researcher on a suite of projects measuring aspects of soil quality across different land use types in Alberta.
This spring, Hernandez published a research paper demonstrating that fractal aggregation is a promising way to assess assessing soil quality. Fractal aggregation puts a number on soil quality, Hernandez says, “and with that number we can assess how far along we are in a trajectory and whether we can recover.”
“There are different characteristics of the soil, and this specific method has the advantage of integrating several aspects of soil quality,” he says. “It’s very consistent and robust, and can separate good management from less beneficial management.”
Over the past three years, Hernandez’ graduate students have led four projects looking at soil quality across Alberta. The main focus of their work was the impact of converting native grassland into annual cropland on soil quality. They found that native grassland has superior soil quality.
Controlled traffic farming
One of the most practical aspects of Hernandez’ students’ work looked at the benefits of controlled traffic farming (CTF) on soil quality. Farming using CTF confine their machinery to permanent tracks in the field, year after year, limiting the impact of heavy equipment moving through the field.
Kris Guenette, Hernandez’ graduate student, worked with Controlled Traffic Farming Alberta, a network of eight producers scattered around Alberta. Each of these farmers compared random traffic to CTF in replicated farm-scale plots.
With controlled traffic farming, field traffic can be reduced to 15 per cent of the field or less, versus the typical 50 per cent seen with random equipment movement, according to Peter Gamache, project lead at Controlled Traffic Farming Alberta. The system requires sizing implements as a multiple of the track width (if tracks are 30 feet apart, equipment must be exactly 30, 60 or 90 feet wide).
CTF systems have been adopted by a handful of Australian producers looking to minimize impacts of drought on soil quality. Gamache says producers in the Alberta program have noticed improvements in water infiltration and soil quality.
“You retain those large pores and allow water and air to move,” says Gamache, “and you have a better environment for root growth.”
“Recurring compaction from equipment is a common factor in reducing soil health,” says Hernandez. Using the fractal aggregation soil test and other measurements, Guenette was able to demonstrate a significant difference between compacted soils in control fields and soils in CTF fields.
The tests showed improved porosity and hydroconductivity in the latter, says Hernandez.
Benefits and challenges
Steve Larocque, a private agronomist and owner of a small grain farm near Calgary, was the first producer to sign on to CTF Alberta more than seven years ago. His interest in the program was piqued, he says, after he did a Nuffield scholarship tour in England, New Zealand and Australia looking at CTF systems.
“You can’t just bolt on CTF and expect miracles,” he cautions. “Like no-till it takes years to see the benefits. With no-till we saw them quickly because we cut back on diesel, labour and power. With CTF we’re already fairly efficient, so it’s about improving soil structure and health.”
But Larocque believes there are significant benefits to CTF. His operation has close to 70 per cent soil porosity, he says, and holds a lot of moisture — “way more” than it did before.
In side-by-side trials looking at how quickly rainfall washes down in CTF versus non-CTF fields, Larocque notes that his CTF fields can handle about six inches of rain in under two minutes; one inch of rain can absorb in six seconds.
“It takes time for your soil to repair and to figure out what benefits you can achieve. For us the biggest one is timeliness,” he says. “How do you put a number on timeliness, getting onto the field when you want to? It could mean an application of fungicide for fusarium when you need it.”
Larocque believes more data is needed on CTF in Western Canada before more producers will sign on.
CTF Alberta’s final report (the project wrapped in early 2017) and Hernandez’ research on fractal aggregation soil testing are a start.
“Essentially we’re trying to come up with a metric to measure sustainability, and this is important for people trying to meet sustainability and productivity goals, and also for customers,” says Hernandez. “We need a solid, robust matrix for measuring the sustainability of our production systems.”