How to measure soil health

Soil Health Institute soil health educator Cameron Ogilvie

Ahh, the wonders of healthy soil. From water-holding capacity, pest and disease regulation, to nutrient cycling and physical stability, a robust and resilient soil gives farmers a huge advantage in crop production.

But what makes a healthy soil? How can we measure its fitness and whether it’s in top farming shape? That’s a question soil health educator Cameron Ogilvie and his colleagues at the Soil Health Institute (SHI) have been digging into to help determine how different soils compare and measure up.

During a presentation at the Ontario Certified Crop Advisors conference earlier this month at London, Ont., Ogilvie noted that his SHI colleagues had compiled a list of more than 30 indicators or measurements that could be used to assess soil health.

That big list includes all sorts of things, including indicators that growers might see on a soil fertility test, and some experimental approaches like new DNA shotgun metagenomic sequencing. Active carbon is a popular measurement, adds Ogilvie.

But 30 measurements can be challenging so the Institute set to work on whittling down the list. They eliminated tests that were not specific to soil health, discarded those already available on soil tests and looked at the practicality of using specific assessments.

“Which ones are accessible, which ones are scalable? And that really relates to price and availability,” says Ogilvie. “Some of these tests are quite expensive. And some of them are just not scalable.” He notes that measuring soil bulk density, for example, is very insightful and provides great information, but it’s challenging to measure, and costly.

After putting all the measures through cost, redundancy, scaleability and accessibility filters, the Institute identified three key measurements that could be used to measure soil health.

“Those for us are organic carbon, carbon mineralization potential and aggregate stability. Those are our big three measurements that we think can work for crop advisors and growers across North America. Those have been tested at research sites across North America and they work very well,” says Ogilvie. (Listen to RealAgriculture’s Bernard Tobin and Cameron Ogilvie discuss key indicators of soil health. Story continues after the interview).

The question now for Ogilvie and his colleagues is how to make this approach workable and actionable for agronomists and farmers. He says a key next step will be to provide measurable targets and references to help assess many variables, including soil type, farming practices, and location, just to mention a few.

“Soil type, drainage, environmental conditions, like annual rainfall, and temperature, all these things kind of set the backdrop or the genetics, if you want to talk about it that way, for a given soil,” says Ogilvie.

“You have to compare similar soils to each other, you can’t compare the health of the sandy soil to a heavier textured soil, it’s just not going to work. Likewise, you can’t compare the health of the soil in Ontario to the health of the soil that’s in Alberta, there’s just a lot of environmental changes that are going on there as well,” he adds.

In the interview, Ogilvie discusses how reference systems are based on soil genetic background. Soil health sampling groups will be created based on soil texture, drainage status, and the environmental constraints of the region. The second step is to sample fields where growers have actively managed the soil to improve health over a number of years to determine which management systems have helped growers improve soil health in the region. The final step is to sample systems that show optimal management and the results it can produce. This reference group includes systems that are typically undisturbed, maintain perennial ground cover, and are not typically part of a row crop system.

“With all these things together, we can start to paint a picture of your soil and where you’re showing up compared to similar soils in your area,” says Ogilvie. The agronomist or farmer could then assess the three different measurements — organic carbon, carbon mineralization and aggregate stability — which will also predict the soils’s water-holding capacity.

Ogilvie says: “All that together can paint a nice, well-rounded picture of how healthy your soil is compared to similar soils in your region, referenced against the best case scenario.”

Ogilvie also discusses next steps for the SHI, including the release of a phone app that could be used to assess soil aggregate stability.