Roots feed microbes to improve soil health

DUNDEE, Ill. — Soil is a dynamic system that contains physical, biological and chemical aspects.

“A standard soil test doesn’t tell us how active the microbes are,” said David Kleinschmidt, owner of Progressive Agronomy Consulting Services.

“Microbes control all the chemical aspects, but the chemical aspects sometimes control some of the physical aspects of the soil,” said Kleinschmidt during a presentation at the Regenerative Grazing School hosted by the Illinois Grazing Lands Coalition. “When all these parts come together, that’s soil health.”

Soil aggregates are formed by biology and plant roots, the consultant said.

“They work symbiotically together and stable aggregates are able to resist environmental stresses,” Kleinschmidt said.

“Soil consists of 25% air, 25% water, 45% minerals and 5% organic matter,” he said. “When it rains, we want the air space to be able to fill up without overflowing.”

If there are aggregates deep in the soil profile, the water will infiltrate and the field can withstand more droughts and floods.

Kleinschmidt showed some examples of soil he dug at the All Grass Farms, where the grazing school was held.

“This soil broke two inches from the top due to compaction and it broke again at six inches, which is the plow pan,” he said.

“Soil remembers, so we can learn a lot from soils by taking a spade and digging a little in our fields,” he said.

“Go to the oldest fence line or tree line on your property and dig there. We want our soils to look like the soil that hasn’t been disturbed for a long time.”

Living roots release root exudates that feed the biology which helps make the aggregates.

“Corn quits releasing those about the time it hits R3 and starts filling the kernel,” he said. “So, with a corn-soybean rotation, we’re starving our soils about eight months of the year.”

Kleinschmidt talked about ecosystem processes that happen everywhere in nature.

“The energy cycle is driven by sunlight energy,” he said. “When you have different plants with different leaf structures — tall, short, fat or skinny — they are capturing sunlight at different levels.”

In a grazing system, the animals trample the thatch material and push it down to the soil surface.

“There are a huge amount of microorganisms in the soil and they need water in the soil profile so they can move around,” Kleinschmidt said.

“The microbes start decomposing the plant residues and about 85% of the carbon in the dead plant material is released into the atmosphere as carbon dioxide,” he said.

“As long as we have green plants growing over the top of it, they’re going to take the carbon up, recycle it and put it back down, which is part of the carbon cycle.”

Plants use photosynthesis through sunlight energy combined with water and carbon dioxide to make simple sugars which are needed for energy in the plant.

“From 30% to 40% of that sugar that the plant produces is leaked out into the root system every day,” Kleinschmidt said. “That usually occurs between midnight and 5 a.m.”

If there are low amounts of moisture in the soil profile, there won’t be much nutrient cycling.

“Plants only take up directly about 10% of the nutrients we apply,” Kleinschmidt said. “The other 90% needs to go through the microbes gut and of that only about 30% of the total fertilizer we apply gets into a plant, so that’s why we have to figure out how to foster microorganisms in soils to unleash the nutrients.”

Different plant species have different chemical composition needs at different times.

“We need to feed different microorganisms in the soil to exchange different nutrients,” Kleinschmidt said.

“With a corn-soybean rotation, we’re selecting for microbes that thrive in a corn or soybean environment,” the consultant said. “If you plant a grass, it might struggle for a little while because we don’t have the microbes.

“That’s where we can use cover crops as a tool to transition into a perennial system,” he said.

Along with diversity, Kleinschmidt said, rest is also important from grazing operations.

“Rest in a grazing system is your biggest friend if you want to propagate more plant species,” he said.