Understanding soil health

THORP, Wis. — Soil is one of the greatest resources found on any farm.

Caring for it and working to improve it should be a constant goal of agriculturalists, according to Richard Halopka, a University of Wisconsin-Extension crop and soils educator in Clark County.

“Someone told me once they had sick soil,” Halopka said. “Soils literally do not become sick. When you talk about being sick, it’s a physical or mental illness — ailing, indisposed, out of sorts. Did you ever see any of these in your field? Probably not.”

Halopka presented “Fixing Sick Soils” at a meeting Jan. 31 in Thorp.

While soils cannot become sick, Halopka said there are many things that farmers can do to improve the quality and function of their soils. Understanding soils and soil health is the key.

Soils have both physical and chemical properties, and they have biology, Halopka said, adding that they are always full of life.

“Chemical properties are the reason why we soil test,” Halopka said. “A basic Wisconsin-certified soil lab test will include organic matter, pH, phosphorus and potassium levels that plants are able to extract from that soil profile and soil water. A soil test is the first step when working to improve a soil.”

According to Halopka, crops need 17 essential nutrients to germinate, develop and put on fruit or grain. In the group are structural nutrients, primary and secondary nutrients, and micronutrients.

“They are all essential, and a deficiency can only be corrected by adding the nutrient,” Halopka said. “If any one of the 17 are in short supply, we may give up yield or not produce a crop.”

Structural nutrients include carbon, oxygen and hydrogen, which are obtained from either water or the air. Halopka said that plants are comprised of 45% carbon, 43% oxygen and 6% hydrogen.

Primary nutrients include nitrogen, phosphorus and potassium; secondary nutrients include calcium, magnesium and sulfur.

Halopka said the physical properties of soil include soil aggregates.

“When the soil guys go digging in a field, the goal is to find soil with a cottage cheese-like consistency,” Halopka said. “Live roots in the soil help improve that. The root hairs give off glomalin that helps produce that aggregation. That is where cover crops or perennial crops become valuable, keeping those living roots in the soil.”

Halopka said the surface cover created by both residues and growing plants benefits the soil by providing food for the biology living in the soil.

“Keeping that cover on the ground helps protect that soil,” Halopka said. “Even today, those soils are alive out there, and that cover benefits that soil biology.”

Other benefits of having cover on the ground, according to Halopka, include reducing the impact of rainfall, improving water infiltration and reducing both runoff and erosion.

Reducing tillage allows soil structure to be maintained and conserves water and is the second step toward improving soil health, Halopka said.

“Each pass of tillage removes a quarter inch of soil water,” he said. “That is water that is in that 60-inch profile. It takes 22 inches of water to grow a 200-bushel crop of corn. That is the amount of water that can be stored in a 5-foot, 60-inch depth of soil.”

Soil biology encompasses any living thing impacting the soil.

“Soil biology can be as large as mice, worms, cows and other animals,” Halopka said. “There are also microscopic fungi and bacteria.”

Halopka said those bacteria and fungi are important to creating the desired soil profile.

“Fungi benefit the most from reduced tillage,” Halopka said. “Fungi like to grow long like a chain. When you go in and do tillage, you cut it off, and it has to restart. The fungi interact with those root hairs and improve the ability of the roots to bring water and nutrients into the plant. That is why fungi are so important.”

Halopka said regardless of the overall health of a soil, all these components are present.

“Even in what I would call a bad soil, there is still all this biology,” Halopka said. “It is just a matter of how efficient they are.”

After soil testing and reducing tillage, diversifying the crop rotation is the next step in improving soils. It is also important to ensure some sort of cover remains on the field to protect the soils.

“Not everyone can do cover crops with their cropping systems, but we can leave residues and plants into that,” he said. “Leaving that residue is like putting a jacket on when it’s cold. You’re protecting that soil from the heat, the cold, the rain. Our soils like it between 50-70 degrees. That is when they are most efficient.”