Focus on a variety of factors to improve soil health

FREEPORT, Ill. — The function of soil is to support crop life, human life and livestock.

Farmers define soil health in many ways.

“We want the soil to help regulate water in fields, to infiltrate water to ground water so we can later drink that water and sustain plant and animal life,” said Dan Smith, southwest regional specialist for the Nutrient and Pest Management Program at the University of Wisconsin-Madison.

“We want a filter area so pollutants are not washed down to the Gulf of Mexico,” said Smith during a presentation at the Northwest Agronomy Summit, hosted by University of Illinois Extension. “And we want structure for the roots to grow.”

Soil fertility is a piece of the puzzle for soil health.

“Corn can yield 500 bushels per acre which has been proven by the yield contest numbers,” Smith said. “The genetics are possible to do it, but we have to manage all the little factors.”

Some of those factors include soil moisture, fertility, plant stands, planter setup, planting time, seed variety and weeds.

“All these things add up and they take away yield by little chunks at a time,” Smith said.

“We could put on 500 pounds of nitrogen, but if we have really low potassium, we’re not going to grow 500 bushels of corn,” he said. “We can say the same thing for soil pH because having the soil pH in an optimum range is critical.”

It is important, Smith said, to get the soil fertility and soil pH correct before it is possible to start building organic matter.

“Organic matter building is going to be dependent on how much residue we can produce, how much residue the field can carry and how much residue we can retain in the soil,” he said.

One way to build soil health is to plant a perennial crop such as alfalfa.

“If everyone could grow alfalfa on one-third of their acres every year, soil health gets really easy,” Smith said. “Because that perennial crop is putting nitrogen in the soil for three to five years, but growing alfalfa is not realistic for a lot of farmers.”

Cover crops are an option for soil health improvement.

“One Wisconsin farmer in Dodge County plants about 5,000 acres of winter rye every year so he is cover cropping every acre he farms plus every acre his neighbor is farming,” Smith said. “He’s doing it with a drill, so it is possible at a large scale.”

Adding small grains to a crop rotation is an option for farmers to consider.

“We can grow winter wheat and frost seed red clover into that wheat which will fix about 80 pounds of nitrogen for the corn crop,” Smith said.

“Manure is a huge component for building soil health with grazing livestock,” he said. “Consumers pay a lot for beef they can see every day, so it’s surprising how many pounds of beef farmers are selling off their farm.”

Farmers can use slake or infiltration tests to evaluate soil health.

“The best is a soil fertility test that ideally you collect the same time every four years,” the specialist said. “That’s your soil report card for comparing phosphorus and potassium over time and to benchmark your soil pH.”

Smith talked about some research projects completed at the University of Wisconsin farms in Lancaster and Arlington.

“For the past five years we’ve been looking at corn and soybeans rotations with a cover crop for biomass accumulation,” the specialist said.

“We need to get to 2 tons of rye biomass to suppress weeds and it will suppress white mold, as well,” he said. “Weeds are an important part of this study and since Lancaster has waterhemp, we’re really concerned about managing waterhemp.”

Several different treatments are part of the research plot including tillage, no-till, early termination, at-planting termination, late termination and forage harvest.

“We are harvesting the ryelage and ryelage is equivalent to alfalfa if you harvest it the right day, but it’s tricky,” Smith said.

In addition, the test includes plots with and without pre-emergence herbicide.

“We apply 160 units of nitrogen, 40 units with the planter and 120 units by side-dressing,” Smith said.

“The last three years have been dry so the rye holding moisture in the no-till fields has been really important,” he said. “It allows the crop to survive a little longer.”

On average, the rye biomass accumulation has been from 2,500 to 5,000 pounds.

“The rye takes off in mid-May when it’s 65 to 70 degrees consistently and puts on a lot of biomass and it uses a lot of water,” the specialist said. “So, you probably don’t want to use the late terminated system in corn because there is too much competition.”

For corn, Smith recommends planting green and then terminating the rye cover crop.

“Rye residue does a tremendous job of suppressing weeds and it does not affect corn yield when you terminate at planting,” Smith said.

“For soybeans, as long as you get them out of the ground, and thriving early on, they don’t care how much biomass is out there,” he said.

The cover crop planted at the Lancaster farm has impacted the waterhemp weeds.

“The winter rye is equivalent to adding another herbicide mode of action into your crop rotation,” Smith said. “It’s really surprising how clean those plots are.”

The corn yields at Lancaster averaged 238 bushels per acre and the soybean yield was 70 bushels per acre.

“In 2019, we grew 99 bushel beans on average across the plot,” Smith said. “Seed-to-soil contact is really important for the planter set up, but the competition doesn’t matter. The only place we saw a difference is the conventional till without a pre-emergence herbicide because the weeds took the soybeans out.”