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Grazing Jump-Starts the Soil, Aids Nutrient Recycling

by Mark Kepler
Fulton County Extension educator and grazier

Published: Friday, September 24, 2021

Grazing in Michiana

I was digging a fence post hole to replace one that had recently broken off. I was using the standard posthole digger that been around for generations. This digger is the type that has wooden handles and pivots where the steel blades slice through the ground.

Digging post holes in August can be quite a job, as the heat and humidity are at their highest, the mosquitoes are at their peak, and the ground can be very dry and hard. Hard enough, that in some years, I would start a hole, pour some water into it to soften it up and come back in a few days and finish the job. The disadvantage to this technique is that the mud will stick to my diggers and be hard to knock out. This year, the ground moisture is better than the typical August, so the water was not needed.

When you first start on a hole, the digging is easy because you are in top soil. This soil has come from thousands of years of trees growing and dying, taking the carbon dioxide out of the air and putting it into tissue (roots, leaves, trunks and branches) that eventually rot away in the soil. There it is called organic matter.

When the Indiana pioneers first came into this forested area and started to till the ground about 5 percent of it was organic matter. When they first plowed the soil, it was fluffy, workable and easy to accomplish. It had tilth. This organic matter held nutrients, water and air. The horse pulling the plow would have found it easy to turn over this soil. It would break into aggregates and peds or, as they would have termed them, clods. These clods would have then broken easily into smaller sizes.

The clodhoppers continued to plow the soil and, in the process, released the trapped carbon back into the atmosphere. The clods consequently became harder and harder. In the 160 years since the pioneers came here, the soil organic matter has dropped to around 2 percent (a 60 percent decrease) and the topsoil has eroded away.

About 5 inches into my post hole, the easier digging stops and the hard clay subsoil begins, which will last for the next two feet to the bottom of the hole. Very few of the historical tree roots were found in this area so the organic levels are very slight. On most of my farm, this subsoil is clay; on another it could be sand or gravel. If we lived on an Indiana prairie soil where some of the grassroots went down over 10 feet and left their organic matter, it could have been easier digging.

I am digging this hole, but as usual my mind wonders and I go back to an article by Cornell University that said, "Livestock provides nutrient cycling in pastures, contributing to soil organic matter, and the grazing action on forage plants encourages root growth and root exudation of plant sugars that feed soil microorganisms.

"For livestock producers, this boils down to a combination of perennial pasture, cover crops in rotation and good grazing management. Perennial pastures, because of the lack of soil disturbance and permanent cover, are higher in carbon and organic matter than tilled crop fields. This biological system has a stable habitat to conduct business, and the nutrient cycles can sustain themselves. However, by adding livestock, we get a multiplier effect on soil health, even in systems that are cropped with a cash crop as part of the rotation.

"Grazing is known to increase soil carbon and nitrogen in the soil. As an animal grazes, it sends a signal to the plant to pump out sugars through its roots into the surrounding soil."

These roots exudate sugars, which become food sources for the microorganisms in the soil.

"The action of grazing jump-starts the soil food web and increases nutrient cycling, making nutrients available to plants," according to Cornell.

I have also excavated hard-digging, hand-blistering, postholes in the dryer climate of western South Dakota, where the prairie grasses are few and far between. The clay there is referred to as gumbo. Organic matter improves most any soil; some just need more of it.

For organic matter, do all you can to hold on to what you have and work to get more. It sounds like a financial statement, and in a roundabout way, it is. Just don't get blisters digging holes in the process.

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