Cates explores soil structure and cover crops at GCP conference

By Heather Cameron
Westwind Weekly News

Anna Cates, a soil health specialist from the University of Minnesota, spoke about soil structure and cover crops during Farming Smarter’s Global Crop Production Conference that took place recently. 

Cates first spoke about soil health principles, saying that the primary principles are to reduce disturbance and increase the amount of time one has a living root in the ground. And cover crops, Cates says, are the primary way to do that.

“You’re having basically a straight effect of plant water uptake, diminishing soil water for cover crops in the spring,” said Cates. “And after this, pretty much our cover crops are killed. So we no longer have the effect of the living cover crop.”

“The longer-term effect of your cover crop after it’s been killed is that you’re going to increase soil water in the system,” said Cates. “Crops are dragging water down when they grow, and probably increasing water retention during the summer.”

Cates explained that the root exudates, and showed in the video the extra carbon or sugars that come out of the root as the plant is photosynthesizing and feeding microbial life. The plant, Cates said, is building its leaves and roots and other biomass, and as it does, it has enough carbon generated from photosynthesis to just slough it off. Extra sugar, Cates said, is in organic acids through its roots. This means that microbes like to live right next to the plant roots, and as they’re eating this plant carbon, they’re also mineralizing other available nutrients. So, Cates said, there is a lot of nutrient exchange right at the root. 

Cates also showed a picture of bacterial cells, which were tiny little balls and fungal hyphae, and said as they’re living on the roots, there is this effect of building soil structure. The biology, Cates said, is supported by that photosynthetic excess that the plants are shooting out, and that’s a sort of nutrient exchange element, but the other element is the physical change in the soil. Cates also showed the macro view, explaining that if some plant roots are pulled out, there are “dreadlocks”, soil clinging to the roots, otherwise known as aggregates. 

Cates even showed a video containing an inside view of an aggregate, which were x-ray scans taken by Dr. Devin Rippner, and said that small aggregates build up into larger aggregates and as larger aggregates form, then comes the binding action of roots and fungal hyphae.

“All of your roots are doing this,” said Cates. “There’s nothing magical about cover crop roots that does this better than other crops. Your corn roots are building soil structure in this way. Your soybean roots, your canola roots, what have you. The point is that the more of your soil interacts with the root, the more structure you’re going to have and the less disturbance you have in your system to break up, especially these stringy roots, the better that structure is going to stick around.”

To summarize the effects of cover crops, Cates said that overall in the water balance, cover crops probably reduce the soil at those wet times of year and fall and spring, and then they should increase the moisture at the dry times of year when there’s enough structure built by them. They’re feeding the microbes and building soil structure while they’re growing, Cates said, and then importantly, they’re reducing erosion. 

Cates then shared information about various research studies she did before concluding.

“Essentially with cover crops, you have this push-pull, said Cates. “There’s this short-term water use from cover crops that can cause a cache crop deficit, but you have this ability of those systems to retain more water due to better structure, and you also have their ability, and that means retaining some nutrients and reducing erosion. When you have the cover crops in the system, our recommendations based on these dry years are to terminate as early as you can. This may be just these last couple years, but I think people are going to be a little bit more conservative on their termination practices. The other thing on the response to rain is that we’re able to show that soil health systems capture a little more rain and that aggregates in these systems can hold together when they’re wetted.”

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