• E-mail
• Print
• Comment
• Font Size
• Digg
• del.icio.us
• Discuss article

Controls Are Key to Testing Compost Tea

Posted on: Friday, 27 August 2004, 06:00 CDT

IN LAST WEEK'S COLUMN on compost tea, I promised information on how to conduct scientifically respectable research in a home garden. Aspiring researchers without enough space of their own may be able to take part through groups like the Master Gardeners, rose societies and fruit growers' clubs, which have access to grounds spacious enough to run a test or two.

Before you get started, you should be aware of a few requirements for your work to be considered scientific. You'll need a control group for each material or technique under investigation, you'll need to eliminate as many variables from the experiments as possible, you'll have to report what actually happens, not what you want or expect the results to be, and you'll have to repeat the experiment. Let's examine each of these requirements in more detail.

Having a control group - that is, a comparison group of plants on which a material or technique you're testing is not being used - is critically important. For example, if we're looking into the efficacy of compost tea as a suppressor of the fungus disease late blight on tomatoes, there should be plants we'll spray with tea and other plants that don't get the tea.

If you're growing susceptible plants, the disease organisms are present and the conditions for infection are favorable, then the control group should get the disease. If it doesn't, and the tea- sprayed group is also blight-free, you can't draw any conclusions about tea as a suppressor of that disease.

Perhaps conditions for infection were unfavorable when you conducted your test, or maybe the variety of tomato you were testing has resistance to the disease.

If the control group gets the disease and the tea-sprayed plants don't, the case for compost tea as a suppressor of the disease is strengthened.

In the unlikely though not impossible event that tea-sprayed plants catch the disease and the control group doesn't, you'll need to entertain the possibility that tea somehow may abet the disease.

Planning for a control group is not difficult; eliminating variables is another matter.

Let's start with the tea itself. Its constituents and the brewing process should be the same for the duration of the testing period (ideally, several years). Keep in mind that there are numerous composts - woody wastes, animal manures and household garbage, to name a few - from which teas could be brewed. Each could be expected to contain a different mix of microorganisms, some of which might control a specific disease or diseases.

Choose one variety of tomato known to be susceptible to late blight for both the test and control groups of plants. Mixing tomato varieties adds rather than reduces variables. If there are varying degrees of disease resistance among three varieties you're using in an experiment, how would you be able to sort out what's happening?

Finally, eliminate variables in the raising of the plants.

For starters, plants in the experiment should be the same age. Set them in similar soil and fertilize, water, weed and otherwise care for them the same way. Remember, when you drench the test group with tea, drench the control group with the same amount of water; otherwise one group will be getting more water than the other.

Your goal is to eliminate every variable except whether or not tea is used on the plants. .

Part of being a scientist is observing carefully and reporting accurately. Don't allow your gardening philosophy to color the outcome of a test. You may hope tea turns out to be an effective non- chemical control for late blight or conversely, that it fails miserably. What you hope or expect doesn't matter. It's what actually happens that matters.

Finally, do the follow-up tests. If you've discovered a truth, for example about compost tea as a disease suppressant, it should repeat itself in further tests. The same results in repeated tests strengthen whatever claims you eventually make and lessen the likelihood you've observed aberrant behavior.

It's what scientists do and it's what scientifically oriented gardeners should do to advance knowledge in the field. Chris Smith, who lives in Port Orchard, is a Master Gardener and is retired from the WSU Cooperative Extension. His columns appear in the P-I garden pages on Thursday. Send questions to P.O. Box 4426, South Colby, WA 98384-0426.

More News in this Category