What’s soil health?
Ask five people that question and you might get five different answers — even among Ag Days experts.
Soil health and soil degradation are getting plenty of time in the headlines, with coverage of last year’s Summit of Canadian Soil Health in Guelph, soil tests looking beyond nutrients and into microbiology and grazing projects on carbon sequestration and its impact on forage growth, to name a few.
The definition of “soil health,” however, has been a moving target, one that has not only evolved since university textbooks started including it, but spans a dizzying array of indicators that may leave producers spinning.
The Food and Agriculture Organization of the United Nations defines soil health as, “the capacity of soil to function as a living system, with ecosystem and land use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health.
“Healthy soils maintain a diverse community of soil organisms that help to control plant disease, insect and weed pests, form beneficial symbiotic associations with plant roots; recycle essential plant nutrients; improve soil structure with positive repercussions for soil water- and nutrient-holding capacity, and ultimately improve crop production.”
That long definition does little for farmers looking for a plan of attack when it comes to improving their own soil health, starting at which soil health indicators they should even start looking at.
Dr. Rigas Karamanos, senior agronomist with Koch Fertilizer Canada and one of this year’s Ag Days speakers, says end goals must be realistic for that soil. A healthy sandy soil will not have the same organic matter as a clay loam, he said, nor should a producer expect it to.
A healthy soil is one that is, “functioning at its optimal levels within its natural settings,” the audience was told.
At the same time, “productivity” should not be confused with “fertility,” Karamanos added, much for the same reasons as he says soil health indicators should reflect the realities of each soil.
“Soil health is not an absolute thing,” he said. “There are some soils that are poor soils; it doesn’t mean they’re not healthy… you’re not going to make them healthy by adding a whole bunch of stuff.”
Productivity and yield must also enter into the equation, he told listeners.
Benefit or buzzword?
Karamanos is worried, however, that soil health has become as much about marketing products for some companies as actually improving soil.
Attention is a good thing when it comes to soil health, he said, but added, it must start with baseline testing, continue with more testing to track changes and all practices must be actually beneficial.
“People say, ‘Oh, soil health? You can apply this, you can apply that,’ but that’s not what soil health is,” he said. “What is the starting point? Just going and indiscriminately applying different products does not fix that.”
For example, nutrients should make up for what the soil does not provide, he said, and a soil’s nutrient status must be known before good management decisions can be made.
The researcher pointed to International Plant Nutrition Institute resources if farmers are looking to learn.
Greg Patterson, president of A&L Laboratories and one of the speakers to follow Karamanos, agreed that not all soils will share the same health standards.
More organic matter has not always meant higher productivity, he said, adding that he has seen Solvita tests from sandy samples return higher microbial respiration, and therefore more microbial activity, than richer soils. His company is one of many to expand into soil health testing.
Patterson says that what many people classify as soil health (aggregate stability, infiltration, moisture capacity, etc.), he would call soil quality.
“My definition of soil health is the whole thing,” he said. “It’s the microbiome. It’s the aggregate stability of the soil. It’s the infiltration rate. It’s the porosity of the soil. It’s the whole thing. But there’s a difference between microbial activity and soil microbial health and soil tilth or soil quality.”
Health or quality?
The Cornell University soil health assessment, something that has emerged as one of the standard soil tests, focuses more on what he would call soil quality, he said.
The report card measures a wide range of indicators including organic matter, soil protein, respiration, available water capacity, wet aggregate stability, active carbon, nutrients, pH and soil hardness.
“When we’re looking at overall soil health, you can’t say you’ve got a good, healthy, stable soil if it’s not producing a crop. So when I see a measurement or something that has a high rating for soil health, but it doesn’t grow anything, I ask why,” he said.
For its part, Cornell University treats “soil health” and “soil quality” as the same term, although it notes that “soil quality” includes all the inherent environmental traits that humans can’t affect.
Do soil health and yield go hand in hand?
Not necessarily, said Steve Crittenden of AAFC’s Brandon Research Station.
“More soil health does not always mean better yields,” he said, although he argued that soil health may come with longer-term, secondary benefits.
Advocates have pointed to better infiltration (one of Crittenden’s markers) and decreased risk of flooding, nutrient cycling, carbon sequestration (something of interest to producers facing down a carbon tax) and benefits of better biodiversity, among others.
For him, he told the Ag Days crowd, soil health refers to water infiltration, compaction, and the ability to retain nutrients, among other aspects that Patterson would refer to as “soil quality.”
Some indicators may be a double-edged sword, Crittenden said. The researcher pointed to studies that suggested more earthworms, commonly considered an ideal of soil health for the average person, may actually increase greenhouse gas emissions from the soil.
The 2013 study, published in Nature Climate Change, found that while earthworms probably help lock carbon into soil aggregates, their gut bacteria also produce nitrous oxide and that their presence could increase both carbon dioxide and nitrous oxide released in the air.
It is also unlikely a producer will be able to reach a peak on all indicators at once, he said, since one indicator will often require a trade-off from another.