8 December 2021

Microbes tell us how the soil is doing. And they help save on fertilizer


It’ s not just about organic matter: microbes are also crucial in guaranteeing a proper soil balance. Now, Canadian and American scientists have developed a new test to capture soil biological activity

by Matteo Cavallito


The analysis of microbial communities allows to evaluate and measure soil health by overcoming methodological problems and offering practical solutions as an alternative to the use of chemical inputs, a research conducted by scientists from the U.S. Department of Agriculture and Agriculture and Agri-Food Canada has claimed. “Understanding the management practices that lead to healthier soils will allow farmers to grow the same crops while reducing costly fertilizers, pesticides and herbicides and protecting the environment,” said Lori Phillips, a researcher at the same government agency based in Harrow, Ontario. Conducted over nearly 20 years, the survey has also uncovered which plants can be most effective in preserving soil balance.

It’s not just the organic matter

In general, scientists remark, a high level of organic matter is a key requirement for soil health. That’s why analyses of soil conditions have historically focused on measuring organic matter itself. But the quantity of the components, which, as we know, increases or decreases slowly, is definitely not the sole factor in the evolution processes of a specific environment. Microbes are also crucial, but their presence can change very fast. That’ s why they need to be measured quickly.

This is why scientists have developed a test called CNPS, acronym of the observed elements’ symbols. The test, in fact, measures the activity of enzymes involved in the four fundamental nutrient cycles in the soil (carbon, nitrogen, phosphorus and sulfur) thus showing the biological activity of fungi and bacteria. The findings have given clear indications.

Microbes offer more accurate analysis

The research, published in the Agrosystems, Geosciences & Environment Journal, issued by the Crop Science Society of America and the American Society of Agronomy, focused on an Ontario farm site and analyzed data collected since 2001. Three crops were observed: corn, soybeans and perennial grass. The microbial analysis – which involved enzyme activity testing and other methods – showed that soils covered by grass and a legume called birdsfoot trefoil, a plant widely found in North America, were healthier, had a greater biodiversity of microorganisms and a larger presence of fungi.

Soybean fields had the worst health status. Corn fields ranked in-between. The evaluation of microbes allowed a better understanding of some important dynamics. It is no coincidence, for example, that the large presence of fungi – which, according to the researchers, reduce soil erosion – was observed in herbaceous areas that obviously had not been plowed and therefore had more time to “build” stronger microbial communities over the years.

Less chemical products, more sustainable crops

The implications of the analysis are clear: “Intensively managed agricultural soils, with more frequent tillage and high fertilizer inputs, tend to be dominated by bacteria. In contrast, more sustainable management practices increase the overall amount of fungi in soil,” Phillips explained. “Agricultural management practices that reduce soil disturbance, reduce chemical inputs,” she added. The study, researchers said, “showed decreased soil health under monocultures, especially soybean, and highlights the need to implement sustainable agriculture practices that maintain soil health.”