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How tillage affects soil microbe populations

TAGS: Soil Health
Lon Tonneson A close up of men's hands holding a mound of soil
SOIL LIFE: A healthy soil contains high populations of soil microbes. South Dakota State University found microbial populations were highest in fields that had been no-tilled for long periods of time.
South Dakota State University compares populations of soil microbes under different tillage systems.

How do tillage systems affect the population of fungi, bacteria, enzymes and other microscopic forms of life in the soil? It’s an important question because they may be key to soil health, which affects nutrient cycling. They are a significant source of carbon and nitrogen, too. In fact, they may represent the biggest pool of those elements.

In 2019, South Dakota State University researchers did a head count of the soil microbial populations in different tillage systems. They looked at long-term no-till (20-26 years), short-term no-till (3-5 years) and conventional tillage systems (fall chisel plow and two spring cultivations) at four sites in eastern South Dakota.

The sites studied were near Beresford, Mitchell, Crooks and Garretson. The fields at each site were close together, often across a fence or property line from each other.

Led by Sandeep Kumar, SDSU associate professor, the team pulled composite soil samples (0-3 inches) from four places in each field. Kumar’s laboratory then analyzed the samples for eight different enzymes, bacteria, fungi, organic carbon and nitrogen.

Results

Udayakumar Sekaran, a graduate student in the SDSU Department of Agronomy, Horticulture and Plant Science and the lead author of an article about the study published in a scientific journal, reported the following results:

  • Most all of the measured enzymes at each location were significantly higher in the long-term no-till fields than in short-term no-till or the conventionally tilled field.
  • The short-term no-till fields had higher enzyme levels when compared with the conventionally tilled fields.
  • In nearly 50% of the short-term no-till fields, the enzyme population was the same as in the long-term no-till fields.
  • The bacteria and fungi levels were higher in the long-term no-till fields than the conventionally tilled fields.
  • About half of the short-term no-till fields had bacteria and fungi levels similar to the long-term no-till fields.
  • Cold and hot water carbon and nitrogen levels were not significantly different between the tillage systems. “Cold” and “hot” refers to the extraction process used to determine the mineral levels. These are newer methods of extracting soil carbon and nitrogen than standard combustion method that has been used in soil tests for years.
  • Microbial carbon and nitrogen was significantly higher in the long-term no-till than conventionally-tilled fields at three of the four locations. Microbial nitrogen and carbon are in the soil microbes’ bodies.
  • Microbial nitrogen and carbon levels in short-term no-till fields was similar to long-term no-till fields at two of the four locations.

What it means

The results indicate that no-till can significantly increase soil microbial populations, and thus soil health, compared to conventional tillage, according to Anthony Bly, SDSU Extension soil fields specialist.

Also, very positive increases in soil microbe populations can occur in as little as three to five years of no-till, he says.

However, inorganic chemistry and agronomy (the standard soil measurements for plant essential nutrients) is still needed for soil nutrient management, Bly says.

“We would like to make [fertilizer] recommendations on the new organic methods and data, but we don’t have sufficient correlations or calibrations with crop response. I believe that someday we will have the calibrations and we can use a combination or both in-organic and organic soil test methods to guide crop/soil nutrient applications.”

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