PRAIRIE DU SAC — “Soil health” is a phrase that has been thrown around a lot lately, but what exactly makes a soil healthy? The U.S. Department of Agriculture’s Natural Resources Conservation Service has their own definition, as do well-known soil scientists John Doran and Timothy Parkin. But according to Richard Lankau, assistant professor in UW-Madison’s Plant Pathology Department, each farmer, too, has their own definition of what makes a soil healthy.
“Soil health is up to us to define,” he said. “Ask yourself, what do you want your soil to do for you?”
With a research focus on soil biology, Lankau shared what he has learned about soil ecosystems and how they affect soil health at the Nov. 28 Wisconsin Fresh Market Vegetable Growers Association Fall School. And while studying soil is complicated, and some things about your soil you will never be able to change, he offered ways to measure how healthy a soil is and how to possibly increase a soil’s health.
While there is no direct way to measure how healthy a soil is, more than a dozen indicators have been identified relating to the physical, chemical and biological properties in soil, Lankau said.
Physical indicators of healthy soil include good aggregate stability, available water capacity, bulk density and good infiltration; these physical indicators are well-known and haven’t changed much in decades, he said. They focus primarily on how water moves through the soil, with these indicators typically being seen and felt on site by simply observing.
Chemical indicators of healthy soil are also relatively understood and focus on the availability of nutrients for crops from the soil. Electrical conductivity, pH, macronutrients like nitrogen, phosphorus and potassium, as well as micronutrients like calcium, magnesium and sulfur, can all be measured within the soil to give an idea of a soil’s health.
While Lankau’s expertise lies within soil biology, biological indicators for healthy soil are by far the least understood. Biological items that can be measured in the soil include organic matter, soil enzymes, soil respiration and earthworms; however, it’s still not clear to researchers how these measures relate to healthy crops and yields.
“Nothing works independently,” he said. “We can’t manage one aspect of soil without impacting another aspect.”
It is said that one teaspoon of healthy soil contains 100 million to 1 billion individual bacteria, with Lankau interested in identifying the thousands of species of microbes and how they are all working within the soil. Microbes, specifically fungi, can increase soil aggregation and the soil’s water holding capacity, but how does a farmer go about enhancing the microbes in their soil?
Farmers can indirectly manipulate the soil through management practices such as reducing soil disturbance, adding biological diversity, keeping living roots in the soil as much as possible and keeping soil covered as much as possible — all practices the NRCS recommends.
But there are also direct ways to manipulate the soil by adding microbes through the use of products known as bio-pesticides and bio-stimulants. Bio-pesticides are used to remove some microbes that may not be desired in the soil while bio-stimulants aim to enhance plant growth by adding some microbes that affect plant nutrient acquisition.
“Microbial products are a big business,” Lankau said. “They can be highly effective, but it’s pretty variable too.”
But before a farmer runs out to purchase a microbial product, Lankau first would pose five questions to see if a product is truly needed. Does my crop need this organism? Is this organism already in the soil? Is some other organism already doing this job in my soil? If I add it, can this organism survive in my soil? If it can survive, can it compete with the microbes already present in my soil?
While it’s hard for a farmer to know the answer to any of these questions, Lankau said his lab is working on developing new technology that could help answer them in the future. Unfortunately, the technology is not available commercially yet.
If a farmer does decide to try a microbial product, Lankau recommended testing the product on a small area of a field. For the best data, he added that a farmer may want to apply the product and monitor disease, yield and plant health on three separate test areas, as well as a controlled area.