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Soil Additives May Increase Your Garden's Beneficial Microbes

By Rebecca Perry
Dallas Morning News
March 19, 2009


Rich, loose soil is teeming with activity that we just can't see. Microbes
including bacteria, fungi, algae and protozoa are busy breaking down plant and
animal material into nutrients that your growing plants can use, aerating the
soil as they go about their business.

There are some fairly common soil additives, including organic compost, humus
and molasses, that may help increase all that activity. Molasses is also an
ingredient in many organic fertilizers.

Experienced organic gardeners say the sugar in molasses is great for the
microbes' diet, and molasses will add a variety of trace minerals and
micronutrients to your soil while you are giving the microbes an energy boost.

A number of other products on the shelves at local feed stores and garden
centers are specifically designed to increase microbial activity. You'll find
them under labels such as "soil activators" and "biostimulants," which are
supposed to increase the microbes already present in your soil, and
"bioinoculants," which contain living microbes. Beneficial microbes help loosen
the soil, bump up the nitrogen level a little, make our soil less alkaline and
promote stronger root systems. However, the word "living" signals some of the
problems with using bioinoculants primarily, that we can kill the beneficial
microbes we are trying to encourage in the garden.

Gardeners need to be aware that this product has a life cycle on it, says Val
Nolen, operational manager at Petal Pusher's Garden Emporium in Cedar Hill.
Petal Pusher's carries Bio Inoculant, manufactured by Texas-based Bio Inoculant
International. The liquid formula contains a diverse population of live,
beneficial soil microbes "over a billion microorganisms in a quart," says Nolen.

These living critters can be applied to your garden with a hose-end or pump-up
sprayer and have the benefit of immediately introducing microbes to your soil.
"We call it liquid aeration," says Ruth Kinler, owner of Redenta's Garden in
Dallas and Arlington. "If somebody's starting an organic program or has really
compacted soil that's where we find it the most beneficial."

Follow the manufacturer's instructions closely. Don't leave the product in the
sun, do keep it at the prescribed temperature, use it within the directed amount
of time and don't use it in conjunction with disinfectants, chlorine products or
antibiotics. Apply the microbes to moist soil and add some organic material
beforehand, so that they have food.

For greatest success, apply bioinoculants when the weather is mild; Ms. Nolen
suggests using them when the soil temperature is between about 50 and 80
degrees, making March to May and late September to November the most likely
ideal application times. If you choose to use them during hotter weather, Ms.
Kinler says to apply it during the early morning or late evening.

Other soil treatments available locally, such as Agrispon and Medina Soil
Activator, are designed to stimulate beneficial soil microbial activity. The
active ingredient in Agrispon is plant extract; Ms. Nolen says to "shake the
living daylights out of the bottle before applying."

While plenty of organic gardeners are willing to share anecdotes about how
biostimulants or bioinoculants have improved their soil or made their gardens
more productive, there are also plenty of scientists who are skeptical that
these products are effective or necessary.

In "Soil Microbiology FAQs" at organiclifestyles. tamu.edu, Texas A&M University
professor of soil microbiology David Zuberer writes: "It has been known for more
than a century that the abundance of microbes in soil is directly proportional
to the organic matter content. Thus soils receiving large amounts of organic
residues support a larger microbial population." However, this is often a
temporary increase.

"To effectively increase organic matter content in soil, we must add more carbon
than the microbes can decompose over a season. Regrettably, adding small amounts
of organic materials like molasses to soils cannot do this. Soil microbes
quickly use up substrates like these and little if any lasting effects are
observed," he contends.

As for biostimulants, Zuberer further advises that testimonials should be viewed
with skepticism. Original data validating the product's effectiveness should be
available, and products should have been tested across locations, climates,
multiple soil types, etc.

"One of our major problems is that we are dealing with biological organisms in
one of nature's most complex of all environments, the soil," Zuberer writes by e-mail.

"It is a dynamic system that changes constantly with wetting and drying, inputs
of organic nutrients, etc. The good news is that for the vast majority of the
time, most soils and their microbial populations are functioning quite nicely.

We simply must pay close attention to the soil environment to ensure that we do
not deplete them of the nutrients required by plants and microbes."

 

 

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