Filed under: General Info
Professional growers and homeowners are inundated with new products that are promoted to “produce healthy plants.” One such type of product is microbial inoculants that can be added to the soil to “replenish” soil or create a “healthy” soil. These products typically are advertised as providing specific microbes that are somehow missing or inactive.
Soils typically are inhabited by huge numbers of a wide variety of microorganisms, and while there is little doubt that the microbial populations that inhabit the soil and colonize the roots of plants are of critical importance, the introduction of beneficial microbes by inoculating the soil is highly unlikely to lead to any significant benefit. First, it is almost impossible to make changes to the existing microbial populations by just adding an inoculum. Newly introduced microbes cannot compete with the existing populations that inhabit the soil in huge numbers. The introduced microbes are not likely to survive or grow if the nutrients and soil environment are not also modified to the degree that they will have a competitive advantage.
University research performed under controlled laboratory conditions and in field trials has clearly demonstrated that in order for any microbial inoculant to be effective the soil environment must also be controlled. In particular, years of research performed with microbial inoculants introduced to the soil to control plant pathogens has shown that the introduced microbes might grow and survive, but they were not effective unless appropriate sources of organic matter (e.g., composts) were also present. In addition, the quality of the organic amendment had a significant effect not just on the ability of the introduced microbes to grow and survive but also on the activity of the introduced microbes.
Although microbial populations in the soil can benefit plant health, plant growers should be aware that the mere presence of “beneficial” microbes is not enough. Unless the soil environment provides proper nutrients, as may be supplied by composts or other amendments, microbes will not produce the level of activity that is sought. In particular, growers should be skeptical of the simplistic statements made by some organizations such as “healthy soils contain typically 25,000 species of bacteria and 8,000 species of fungi.” This statement implies to the reader that adding species or numbers of microbes will have some benefit. The reality is that the activity of the microbes is most important and long-term changes to microbial activity in the soil will likely require changes to the physical and chemical structure of the soil. The introduction of organic matter through soil amendments is one important way to make long-term changes to the soil environment that will in turn promote changes in microbial populations and microbial activity.
The soil microbial community is amazingly complex and although it is often attractive to make simple statements about the benefits of products, growers and homeowners looking to improve the soil should carefully evaluate claims that promise simple solutions to complex problems.
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