SOIL MICROBIOLOGY FACT AND FICTION

Dr. Roch Gaussoin, a turfgrass scientist at the University of Nebraska, recently wrote about turfgrass microbiology “fact and fiction” in the newsletter for the University of Nebraska's Center for Grassland Studies. Gaussoin noted that recent research is casting doubt on certain “truths” that have been accepted for years. Among them:

  • Excessive pesticide applications harm soil microbiology.
  • Sand-based root zones are nearly sterile.
  • Soil inoculums/additives can alter soil microbiology.
  • Turfgrass soils are lower in microbial biomass and diversity than other soils.

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Research conducted on the greens of 16 Nebraska golf courses from 1996 to 1998 calls these assumptions into question. The courses were classified into three groupings based on their level of management inputs, and their soil microbiological properties were assessed. Among the findings:

  • The age of the green was the most significant factor in microbial abundance and diversity.

  • Management level, including higher pesticide inputs, did not affect microbiology.

  • Within 18 to 24 months of establishment, greens soils exhibited significant microbial populations.

  • The microbial biomass 18 to 24 months after establishment exceeded that of traditional row crops, but was less than native, undisturbed soils.

Gaussoin explains that microbial populations are associated with organic matter rather than the mineral fraction of soils. Consistent with other published research, then, these results suggest that increasing microbial populations after green establishment correspond to organic matter increases in the root zone.

Gaussoin also questions the value of microbial inoculants to mature soils, noting that labeled application rates of many of these products result in a ratio of one applied microbe to 6,000 native microbes. At this proportion, it is doubtful that the applied inoculants stand a chance of competing with existing microbial populations.

However, newly established soils, where existing populations are low, might benefit from inoculants as an aid to more rapid establishment. This is suggested by the results of another Nebraska study, in which inoculants appeared to speed green establishment compared to traditional grow-in.

The full story is available online at the Center for Grassland Studies Web site at www.grassland.unl.edu.

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