Microbial Soil Amendments: New Information and New Generation Technologies

By Dr. Robert N. Ames, senior staff scientist, Advanced Microbial Solutions, LLC

Fig. 1 ?EUR??,,????'??High bacterial counts do not necessarily translate to high metabolic diversity. Each well in the upper plates contains a different bacterial food source. Color development indicates the ability of the bacteria to use that particular food base. Lower plates show the bacterial populations being compared in the metabolic testing plates above.

In public forums or educational events, I am often asked to describe the various groups of soil microorganisms, and explain how they could be encouraged in the soil. In the landscape industry, however, few superintendents manage their soils with the specific objective of encouraging soil microorganisms. This is not to say that they dismiss them as being unimportant, it?EUR??,,????'???s just that the tools are not available to manage soil microbiology along with maintaining plant growth, disease control and soil fertility.

I thought it would be helpful to share my views about the state of applied microbial products and some of the advances in microbiological research driving a new generation of microbial products.

Fig. 2 Reducing compaction with microbial products. The data shows a reduction in soil compaction in only six weeks using a microbial fermentation product. Note that the untreated lawn at the same site actually increased in compaction over the same time period.

Experiences with Early Microbial Products

Many of the first commercial microbial products consisted of one bacterial (or fungal) species selected to stimulate plant growth or help with disease control.

The failure of many microbial products was attributed to not increasing the population of soil organisms above levels in untreated soil. A related view was that, even in highly managed systems like turf, all the microorganisms required for a healthy soil environment were already present, based on performing counts of microorganisms growing on Petri plates using a limited selection of nutrient media. Plate counts are still in wide use, but modern genetic research has shown only about one percent of the total numbers of bacteria in the soil are detected using this method. In that sense, conclusions about how microbial products affected soil microorganism populations were based on evaluating less than one percent of the total population?EUR??,,????'??+arguably not a good representation.

Auburn also tested turf, here ryegrass. Whether it?EUR??,,????'???s turf or ornamentals, your plants will benefit from microbal soil amendments.

New Generation Microbial Products

Microbial products with a greater number of species or ?EUR??,,????'??counts?EUR??,,????'?? of microorganisms are perceived better than products with lower diversity and counts. New technologies and product approaches challenge this view.

Consider the analysis techniques of what the microbes do, rather than counts alone. The principles of metabolic function are fairly simple. Microorganisms able to consume (or metabolize) a greater diversity of food sources in the soil should have an advantage for surviving and performing the required soil functions. A helpful analogy is the microbial community as a city. Envision two cities, one with a population of 100,000 who, oddly, share only one or two job skills; the second city has only 1,000 people, but with job skills to cover all required services for a large city. Now, envision you urgently need double by-pass heart surgery. The large city has only plumbers and electricians; the small city has those skills, but also heart specialists. Microbial products with high-metabolic diversity (?EUR??,,????'??skill sets?EUR??,,????'??), but fewer total microorganism (population) counts, just might provide better performance than very high numbers of a less metabolically diverse product.

Fig. 3 Similar grow-in sites at the Kennsington Golf Club, Canfield, Ohio, comparing a turf treat with a microbial-based soil amendment (right) and untreated tees. The grow-in, root development and turf coverage on the new course has been dramatic, according to Sean Novotny, superintendent at Kennsington. ?EUR??,,????'??It has enabled us to get our turf ready much earlier than expected, about a month ahead of schedule. There is a 100 percent difference between the turf treated compared to the turf that was not treated.?EUR??,,????'??

An example of this can be seen in Figure 1. This figure shows evaluations of extracts obtained from a microbial soil amendment and a composted poultry manure product. Petri plate counts show the compost, on the right, had a greater diversity and number of microorganisms. However, based on the diversity of food sources used?EUR??,,????'??+as shown by the top row of plates?EUR??,,????'??+the microbial soil amendment product had a much larger degree of microorganism metabolic functioning.

Advances in fermentation technologies allow development of large, interactive microbial communities?EUR??,,????'??+a major step forward from synthetic blends of a few strains of cultured species. Microorganisms continuously communicate with their environment and each other via chemical and biochemical signals. These signals communicate whether conditions are favorable for growth and food is available, or if the microbes should shift into a survival mode. Certain nonculturable bacteria require one or more different species of bacteria to grow, and fermentation technologies take advantage of the biological and biochemical interactive nature of microorganisms and direct these resources to benefit plant and turf growth.

?EUR??,,????'??Microbials products have definitely improved the quality of our St. Augustine grass. Our turf has better color and density, which I can attribute to reduced soil compaction.?EUR??,,????'???EUR??,,????'??+Gregg Newcamp, district manager, Busch Gardens, Fla.

One problem of early generation microbial products was they contained only one or even a few species of laboratory-grown microorganisms. They carried with them the biochemical signals and physical conditioning of their nutrient-rich, ideal growing environment. When placed in soil, the growing conditions were certainly not ideal. Fermenting ?EUR??,,????'??in community?EUR??,,????'?? represents a way to better prepare microorganisms into the soil. The focus on the soil (and microbial solutions to its problems) aims to improve the environment for healthy and sustained growth, rather than merely targeting direct stimulation of the plant.

An example of this potential, Figure 2, shows how a microbial fermentation product worked in soil to reduce compaction in as little as six weeks. Figure 3 shows how the microbial soil amendment product added to the standard management practice dramatically improved the rate and quality of turf establishment for the grow-in of a new golf course.

Auburn University tested various plants to see the growth results of plants treated with microbal soil amendments. Guess which plant was untreated.

Current and Future Applications for Microbial Technologies

Microbial fermentation technologies produce a very stable product with an extended shelf life. This stability allows for product combinations that can protect the microbial and biochemical aspects of the newly combined product.

Further Auburn University tests revealed the root development with and without microbal soil amendments. These transplanted New Guinea impantiens are six weeks old.

Getting Started

Landscape superintendents should take a proactive role in selecting microbial amendments, and once the appropriate product is selected, set up testing procedures to help validate the performance. Most importantly, the evaluation should be designed in such a way that the user can gain firsthand insight into what is happening and what results are achieved. To that end, Figures 4 and 5 outline some useful considerations for selecting and testing microbial soil amendments. Microbial products are not identical in content and performance.