The benefits of soil testing

A garden plot converted to soybeans gave Ron Snyder a glimpse of the complex processes at work in the soil on his farm near Pemberville, Ohio. Snyder and his wife, Barb, had applied compost to the garden spot the previous year. The next year’s soybeans stood a foot taller than the beans in the rest of the field and had fuller pods.

Intrigued by the difference in plant response, Snyder began to learn all he could about the inner workings of the soil, and how he could put that knowledge to work in the growing of corn, soybeans, and wheat on his 200-acre farm. He began a regimen of soil tests to evaluate the soil’s functions and measure its biological life. After a decade and a half of managing for soil health, the tests indicate the progress he’s made and suggest ways to reduce inputs.

“I will take a Haney soil test, for instance, and then I will make a decision about how much nitrogen to apply,” he says. “Yes, the tests are expensive, but so are applications of nitrogen, phosphorus, potash, fungicides, and insecticides. After reducing these applied inputs, I am making a lot more money now than I did before I started making management changes and testing for the results.”

One change Snyder made years ago was switching to no-till. His primary motivation then was saving time, so he could farm as well as teach full-time.

But hand in hand with the switch to no-till came a growing frustration with his soil. “The farm Barb and I had bought had heavy clay soils,” he says. “Heavy tillage left the soil biologically dead. We had a water-infiltration problem. Even if you did till the soil, the water would just sit on the surface.”

Incorporating cereal rye

Beyond no-tilling, Snyder’s early effort to improve the soil was to plant cereal rye as a cover crop. He planted the rye after harvesting corn in late October. By May, the rye stood 6 feet tall. Despite his apprehensions about planting into such a tall cover crop, Snyder no-tilled soybeans in 15-inch rows into the green rye, terminating it soon after.

“The soybeans came up fine, and the crop looked good; I thought I was on the right track,” he says.

However, the cash crops struggled in the second and third year of growing a cover crop. “By the fourth year, the crops started to look better, and they just kept improving,” he says. “It took about three years for the soil to become biologically active.”

Soon after, Snyder began measuring soil respiration. Measuring the soil’s ability to breathe via a CO2 burst test indicates the amount of microbial activity in the soil, according to an interpretation guide for the Haney soil health test, one test designed to measure respiration, along with other soil health indicators. Microbial activity is tied to nutrient cycling, soil aggregate and organic matter formation, disease suppression, and stimulation of plant growth.

“I found that my soils tested lower than average for respiration even after four years of growing cover crops,” says Snyder.

To boost soil health further, Snyder, who was named a Soil Health Champion by the National Association of Conservation Districts, began growing more cover crops. Today, he plants a multispecies cover crop after every cash crop.

Soil organic matter has increased as a result. Before growing cover crops, the farm’s soil organic matter was between 2% and 3%. More recent tests show that organic matter has increased to 4.6%.

Over time, Snyder also broadened his testing of soil health indicators. He began testing for the nutrient potential in the soil. The testing lab supplies a total nutrient digestion analysis quantifying both the plant-available and -unavailable nutrient pools.

In May 2022, test results showed Snyder’s soils had 39 pounds per acre of available nitrogen and 52.5 pounds per acre of available phosphorus. The results indicate that phosphorus levels in the soil have stabilized in response to the biological activity in the soil, despite Snyder ending phosphorus and potash applications in 2011.

He has reduced nitrogen applications as well. By combining the measurement of available nitrogen in the soil with the measurements from CO2 burst tests, Snyder estimates potential reductions in applied nitrogen. Sustained crop performance justifies the reduction.

“In 2022 I planted corn into a cover crop of 17 species,” he says. “I planted the corn without applying phosphorus or potash, of course. Afterward, I sidedressed with 75 pounds per acre less nitrogen than the conventionally recommended rate. It was the second-best corn crop I’ve ever raised on the farm.”

Evaluating soil amendments

To evaluate whether various soil amendments benefit crops and soils on his farm, Snyder uses a combination of soil health tests. Working with an agronomist, Snyder set aside test plots to evaluate the benefits of a biological soil amendment. He planted corn in a treatment plot and also in a control plot. Neither plot received fertilizer applications, but the treatment plot received the biological.

During the growing season, the control plot had a little more than 79 pounds per acre of available nitrogen and 147 pounds per acre of available phosphorus. The CO2 burst showed a rating of 67 ppm.

The treatment plot receiving the biological had a little more than 68 pounds per acre of available nitrogen and nearly 129 pounds per acre of available phosphorus. The CO2 burst had a rating of nearly 143 ppm.

“While the CO2 burst was higher on the plot treated with the biological, there was no real difference in crop yields between the two treatments,” says Snyder. “That was the fourth biological I’ve used with no yield difference on my healthy soils.”

To monitor how his management practices and fertilization rates are affecting plant health, Snyder does plant sap analyses. The tests measure the nutrient concentrations in the plants at the time of sampling. The tests so far indicate his plants have sufficient phosphorus, and corn has excess nitrogen when Snyder applies it at a rate of 125 pounds per acre. “That tells me I can consider reducing nitrogen applications further,” he says.

“Getting soils healthy is the key,” notes Snyder, “and testing shows me whether or not I’m on the right track.”