Dr. Grow: Soil needs microorganisms as well as nutrients

I can still remember the first day my soils class met in college. The professor walked into the classroom and said, "If anyone ever uses the term dirt to refer to soils in this class, they will automatically flunk." He didn't even say hi, how are you, my name is ____, or anything else. He then began to talk about soils.

It took me a long time to understand why he said what he did. I think I now have a good feeling for why he started the class this way. Most people think of soil as dirt -- a combination of clay, silt and sand particles. But a soil is far more complex than that.

In a sense, a soil is a living, breathing entity. Of course, soils are made of clay, silt and sand particles. But a good soil also includes air spaces filled with oxygen, carbon dioxide and nitrogen along with plant roots, both dead and alive, and water.

You also find in soils a plethora of microorganisms such as nitrobacter, nitrosomonas and rhizobium, just to name a few. These organisms are responsible for breaking down organic matter and for changing fertilizers into the right form for plant use.

Of course you also find earthworms, insects, seeds and an occasional mole and vole in good soils.

Soil quality can be improved by adding compost. (Fred Lynch)

I mention all of the constituents of a good soil for a reason. When new gardeners, and also many old-time gardeners, ask me to evaluate a soil, they are only interested in the levels of phosphorous, nitrogen, potassium, calcium and maybe a few of the micronutrients along with pH. They never ask me to evaluate soil structure or soil microorganism concentrations.

As I have mentioned above and in my last column, you need to evaluate a soil not only for nutrients and pH, but also for soil structure, and micro- and macroorganism content. All three conditions must be met for your garden soil to be a sustainable soil that can produce a bumper crop of tasty vegetables and prolifically blooming flowers.

In previous columns I have discussed how to correct pH and nutritional deficiencies and how to change soil structures. Today I want to suggest some things that you might do to increase microorganism content in your soils.

First and foremost, you want to add organic matter to your soils. This can be in the form of leaves, well-dried grass clippings, old sawdust or peat moss. These materials will provide substrates for the work of some of the microorganisms that will be present in your soils. Whether your soils are sandy or have high clay content, organic matter is important.

As microorganisms work, they will multiply and their concentration in your soils will get higher. If you want to speed up the process, add manures and compost to your soils. The manure and compost usually have high concentrations of the microorganisms that are needed for a good sustainable garden soil.

Although the textbooks say that too much organic matter is not good, I think I can safely say that most soils in the Heartland are poor in organic matter. I doubt that you can add too much organic matter in our soils.

If you decide to add compost to your soil, remember not all composts on the market are the same. Find one that has a lot of organic matter coming from both plants and animals. This combination will give you the best results in terms of building the population of essential microorganisms and macroorganisms in your soils in the shortest amount of time.

If you think of a soil as a living and breathing entity, you will be conscious of the need for proper amounts of soil nutrient levels, proper soil structure and proper concentrations of organisms. When you achieve this balance of all components, you will find your work as a gardener is much easier, and your results in terms of beautiful vegetables and flowers are much better. Have fun in your garden this growing season.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699, Cape Girardeau, Mo. 63702-0699 or by e-mail to news@semissourian.com.;