Cover article - Published June 2007 - Turf Magazine (all regions)

When you're talking about microbial soil inoculants, it's kind of a he-said, she-said situation. You've probably heard it all before if you're a turf manager: promises from the product sales people and cautions from the turf scientists. At the risk of getting in the middle of a domestic dispute, this is what the two sides say.

Manufacturers promise a lot, and they have a lot of testimonials and some test information to back up those claims. There are some prominent companies using sophisticated methods to brew up microbial inoculants for use in agriculture and landscaping, and there is a common-sense basis to their claims. It's all based on the premise that healthy soil has a busy population of millions of organisms, from bacteria to fungi, which till the soil, change its chemistry, create pores, inhibit soil pathogens, enable plants to utilize fertilizers more effectively and conserve water. If your soil doesn't have many of those organisms, it makes sense to add them.

Among the many benefits claimed by manufacturers of microbial inoculants is the improvement of water conservation, as on this baseball field in the Phoenix area. 

What do the scientists say? Basically, the data from rigorous scientific tests on turf don't show much results. Turf researchers who have tested these "bugs in a jug" amendments, as one scientist calls them, say that soils already have billions of these microbes in a few pounds of root zone, and adding a quart or gallon per acre doesn't seem to affect turf growth. Especially when these foreign organisms may be quickly eaten by the natives.

"We don't know enough about these inoculants," says Frank Rossi, an associate professor in turfgrass science at Cornell University. He has conducted several studies over the years, including a recent one testing several kinds of microbial amendments, and he has found little or no evidence for the claims that manufacturers make.

One positive finding was that some inoculants appear to enable turf managers to get good turf growth with fertilizer rates 20 to 50 percent lower than normal, but all claims that microbes alone devour contaminants, promote grass growth, improve soil tilth, reduce salinity or save on irrigation water don't pan out. "I tend to believe that some of these statements don't seem credible," Rossi says, and he has also reviewed many other scientists' studies looking for positive results.

Rossi points out that golf course superintendents often are impatient with him, because many use inoculants and seem to see results (his recent study was funded by the Golf Course Superintendents Association of America and the United States Golf Association). However, those testimonials are unverified by data, and as such, most scientists withhold their approval. He says that the science is uncertain, with microbiologists unable even to define what a "healthy" soil is in regards to microbes. When turf scientists can't find positive results, they assume that turf managers are looking at uncontrolled and unscientific comparisons.

"For the people who are using these inoculants, I think they're deceiving themselves," Rossi says frankly. The manufacturers think differently.

One company with some positive indications from its product is Environmental Techniques International, with its CBX bio-organic liquid inoculant. ETI has been busy around its Arizona offices testing CBX, and has gotten some good results though not in randomized tests. It's instructive to see what one of these products consists of and how it is produced.

Jason Bentz is ETI's technical director and does a good job of explaining the properties of CBX. Using as a base Leonardite, a mineral excavated from an Idaho site, the company says it activates the preserved microbes lyingdormant in the material. The water-soluble minerals and plant material deposits yield a loose material that contains many living microbial organisms. This is brewed up in a sophisticated "digestive process" where acids, enzymes and other additives create a commercial product that is sold as a liquid.

"We don't sell it as a fertilizer," Bentz notes, but as a soil amendment that allows the normal NPK granular fertilizers used on turf to work more effectively. CBX corrects imbalances in the soil through the activities of the microbes, he says. It is added to irrigation water in various ways and is sold internationally.

On some turf, such as at a Salt River Project water conservation study in Phoenix, CBX showed it was effective in lowering water requirements by opening pores in the soil and allowing water to penetrate better. There, it was sprayed onto the turf via a portable ATV-mounted unit and then watered in with the sprinklers at the facility.

"Our best results are to water it in," Bentz says, though he notes that CBX can stand on turf for a while and not burn it. The results were good turf quality on a baseball field as well as the elimination of standing water in retention basins.

At Sanctuary Golf Course in Scottsdale, an Audubon Society Silver Certified Golf Course, CBX was found to have contributed to a decrease in water consumption of 122 acre feet over the last five years, Bentz says. There, the amendment was automatically injected from a 50-gallon drum to the irrigation system's supply line and sprinkled onto the turf during normal irrigations.

Global Organics is another company producing a microbial inoculant. Its Humega product from the BioFlora line is used for both agriculture and landscaping plants, and the company's vice president of sales, Terry Gooch, says it has been tested and used extensively on turf.

Gooch notes that the product, which is basically a liquid compost, opens up the soil and helps create humus and gives the soil more water-holding capacity. It has a variety of enzymes and six groups of microbes. It also has a nitrogen-fixing bacteria in the mix, he says.

In addition, Gooch says, the company has noticed in its tests that Humega has a slight "pathogen inhibition characteristic" that helps avert infestations of soil-borne pathogens like phytophthera. The product is also a liquid formulation that, like CBX, is based on Leonardite, with a microbial and enzyme package added. It also tests out with over 70 trace minerals, he claims.

Another take on this is from the Sustainable Studies Institute, a non-profit offshoot of the Soil Food Web in Corvallis, Ore. This group uses compost teas loaded with microbial organisms to do the job of reactivating the soil.

Joe Whaley, executive director of the institute, says this is a research and education group that works with independent consultants in the U.S. and Canada to promote the introduction of inoculants into damaged soils. Their approach is to use compost teas, either commercial or homemade, to promote a wide range of bacteria and fungi. Once established, the microbes may or may not need further assistance, and further treatment will show declining results because the microbes are already there.

Whaley says there are typically 25,000 species of bacteria and 8,000 species of fungi in healthy soil. The SSI advisors work with a lot of turf facilities, especially golf courses, including some prominent ones on the Oregon coast, and their tests show that compacted and unhealthy turf will have a fraction of the organic life it needs to recover.

Compaction is a big issue on golf courses and school grounds, Whaley says. However, by using either a soil drench or a foliar spray of compost tea, the turf manager is introducing a long-term cure. Repeated treatments and testing may be required. The microbes follow the roots of the grasses down to the compaction layer and begin consuming the pollutants as well as creating spaces in the soil.

Where an anaerobic condition once existed, a complex web of microbes opens the soil and roots up to oxygen and the movement of other organisms, Whaley says. He has seen it happen many times.

Keith Karnok, professor of crop and soil sciences at the University of Georgia, has run tests in the past on microbial amendments, and he also gives seminars to the GCSAA on this topic. He reviews other scientists' work religiously and talks to them about it.

"We get into the microbial enhancement of soils. We just have a hard time understanding how this works," Karnok says. He notes that there is "some evidence" that there may be some effect in certain studies, but that the preponderant weight of evidence is that the data show little or no positive results on turf or turf root growth.

Karnok himself has tested such compounds in UG's "rhizotron," a controlled growth chamber that would show root enhancement if it happened. It didn't. He admits that this was years ago, and maybe the products have improved since then. He says these microbial inoculants are in a "gray area" of regulation, in which if they are not advertised as fertilizers they don't have to guarantee a nutritional boost or growth.

The bottom line to Karnok: if he can't see data supporting efficacy, he can't recommend the use of such supplements to turf managers. The odd thing is, he has taken surveys of hundreds of golf course superintendents and found that 40 percent of them use these products regularly; another 40 percent use them periodically. The superintendents often say they see benefits, though they are not validated in randomized tests and, as such, are purely anecdotal.

"We've never seen a negative effect," Karnok points out, so he doesn't try to discourage a turf manager looking for a way to boost turf growth from using microbial inoculants. He just can't see much if any effect of these products, and they are relatively expensive.

One more observation from Dave Zuberer, a Texas A & M University professor of soil and crop sciences: "What we've learned over the years is, it's darned difficult to inoculate the soil." There are not many positive responses if you look at tests done across the country.

From his work with microbes, Zuberer has learned that the sheer bulk of microbes that exists in native soil, even poor soil, make it unlikely that a turf manager will be able to improve those populations by adding a gallon of them per acre. He and Karnok agree that a good way to enhance a soil's microbes is to add more humus, mulch and compost to get organic matter for bacteria and fungi to live in.

That will improve microbial activity and make better turf. No controversy about it.

Web resources

Turf managers who want to do comparison can find a lot of information. Below are some handy Web sites, and of course, they can contact their Cooperative Extension or various turf association offices for advice.

• Advanced Microbial Solutions is another company supplying microbes:

• Environmental Techniques International's product, CBX:

• Global Organics produces a microbial product used on both turf and agricultural crops:

• The Soil Food Web site has good explanations of soil microbial activity:

• The National Sustainable Agriculture Information Service also provides information on microbes and compost: