Soil fertility is about more than nutrients

Expert says farmers need to learn more about the physical and biological structures of the soil

Many farmers tend to focus on the chemical composition of the soil, and ignore its other two key components — and that’s a mistake, says a crop and soil nutrient management specialist.

“Farmers need to understand more about the physical and biological structures of the soil to manage their cropping systems,” said Yamily Zavala of the Chinook Applied Research Association in Oyen.

“You might not be solving anything just by applying soil minerals. The problem could be physical. If you fix the physical, then all of the factors could be integrated to improve soil health.”

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Zavala, who studied soil health at Cornell University and hopes to create a soil lab for her association, recently toured the Peace to talk about what makes soil healthy. One of her key messages is that the three components are interrelated, which is why upping fertilizing rates doesn’t guarantee higher yields.

Take for example, aggregates, which are formed when soil particles bind together, but broken apart by tillage and compressed by compaction. Aggregates are full of little holes, and that improves soil’s ability — often dramatically — to soak up and hold water.

“Good soil aggregates should act like a sponge, with porous space and more space for air, so there’s room for both roots and water,” said Zavala.

Aggregates can also be affected by a lack of cover. So bare fields are not only more susceptible to erosion, but the soil in those fields may be losing some of its physical structure as aggregates dry out and become less stable.

What’s growing above ground is also critical to the microbial life below.

The more diverse the plant life being grown, the more diverse the microbial populations, which play an invaluable role in converting nutrients into the forms that crops can utilize. As well, mucilage and wastes released by the micro-organisms help the soil to form aggregates.

It is a vast and intricate web, but the bottom line is simple.

“When the (plant) populations are diverse, the soil is improved,” said Zavala.

She pointed to an Australian study that compared two very similar soils save for one difference — the amount of microbes. The one with the high micro-organism population resulted in improved uptake of nitrogen and minerals and, not surprisingly, yields were higher. There was also less nitrogen and mineral leaching.

So what’s Zavala’s advice for growers?

In addition to avoiding tillage and summerfallow, she recommends cover crops as a way to restore soil health. Sometimes the improvements can be quick, she added. She planted cover crops on a compacted field, and in just two months, saw a huge difference in the area that was planted with cover crops compared to the chemfallow portion. Six months later, the same soil contained more aggregates and was significantly less compacted.

She also advises learning more about micro-organisms and the benefits they bring.

“The different microbial populations can even reduce soil-borne diseases and plants will be healthier,” she said.

About the author


Alexis Kienlen

Alexis Kienlen lives in Edmonton and has been writing for Alberta Farmer since 2008. Originally from Saskatoon, Alexis is also the author of two collections of poetry, a biography, and a novel called "Mad Cow."



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