[font family=”impact,chicago” size=”36″ color=”157801″ textshadow=”6″ alignment=”left” weight=”bold” style=”normal” lineheight=”120″]Ohio State University[/font]

OSU RESEARCH UPDATE

Growing Plants with Worm Poop:
Vermicompost as an Amendment for Soilless Media.

By Dr. Jim Metzger
Professor and D.C. Kiplinger Chair

Today most floriculture crops are produced in soilless media that often contains an organic component. Certainly peat is one of the most widely employed organic materials contained in commercial soilless media. However, as peat supplies diminish because of over- harvesting, prices will inevitably rise. Therefore, identification of comparably priced substitutes for peat is imperative. One approach is to amend peat-based soilless media with other organic materials such as carbonized bark and compost. While these substances are not intended to substitute for peat, they do reduce the amount of peat used by 10 to 20%, while at the same time alter the physical and chemical properties of the media to provide optimal growing conditions.

At the same time there is growing environmental concern about the disposal of organic wastes such as sewage sludge, yard and garden waste, and animal manure. Therefore, bio-solid wastes must either be contained or converted to a non-hazardous form that will not pollute the environment. This, of course, has led to the skyrocketing of the cost of disposal. Composting such wastes is one environmentally sound way to convert biological waste into a form that can be easily disposed and provide a mechanism to recoup some of the costs incurred.

Incorporation of compost into potting and container media is one potential use for this material. Indeed, the addition of compost has been shown to contribute positively to the chemical and physical properties of potting media. But there are downsides as well; foremost of which is the difficulty in producing a reproducible and stabilized product. The primary reason for this is because the composting process is dependent on the aerobic action of soil microorganisms that break down the complex organic molecules to simple substances that can be taken up and utilized by plants. This bio-oxidative process is highly dependent on variable environmental conditions such as temperature and the availability of oxygen that are hard to control.

Another “composting” process that has not received as much attention is vermicomposting that relies on the action of earthworms to break down complex organic compounds. The worm castings or fecal material produced by the worms is a rich source of a variety of essential plant nutrients. In contrast to conventional composts, vermicomposts are less variable and much more stable. In addition, the time to complete the composting process is much shorter for vermicomposts: one pound of worms can convert one pound of pig manure to compost in 48 hours!

Could vermicompost be an economical and useful amendment to soilless potting media? To answer this question, Gary Bachman, a graduate student of mine, and I have been collaborating with Drs. Clive Edwards and Scott Subler from the Entomology Department at The Ohio State University. We have been examining the effects of vermicompost, derived from pig manure, on the growth of bedding plants and assessing whether or not the use of vermicompost in commercial soilless media is economically viable.

In initial studies we found that incorporation of vermicompost in a commercial potting mix resulted in faster growth, increased height, and higher fresh and dry weights for a variety of bedding plant species. The optimal amount of vermicompost need to produce positive results was relatively low: between 10 and 20% by volume. We found that the incorporation of vermicompost in the media essentially eliminated the need for additional fertilizer in the production tomato plugs. These results suggest that the routine incorporation of vermicompost in soilless media may provide the grower with significant savings in plug production by reducing the costs associated with fertilizing.

We also observed that the positive effects of the vermicompost on plant quality were sustained for a substantial period of time after seedling emergence. In other words, incorporation of vermicompost in media used to grow bedding plants may help to maintain crop quality and salability even after the plants reach the garden center. Additional evidence for this was obtained through a consumer preference study conducted prior to an OSU football game involving nearly 400 adults. An overwhelming majority (around 80%) of the participants said that they would choose to buy tomato plants grown in media amended with 10% vermicompost over those grown using standard fertilization methods.

Although much of the effect of vermicompost on plant growth can be attributed to the addition of important nutrients, there are other unknown factors involved. Plants grown in vermicompost-amended media still grow better than those grown in unamended media with similar nutritional levels. Furthermore, the promotive effect of vermicompost on growth is lost if it is sterilized and can not be restored by adding additional nutrients. We are presently trying to determine the nature of the factor(s) contained in vermicompost that promote plant growth.

Regardless, the use of vermicompost in commercial soilless media holds great promise if the economics hold out. The widespread use of vermicompost as an amendment will ultimately depend on its cost of production. However, with the increased pressure to find alternate ways to safely dispose of animal manure, the techniques for vermicomposting on a large scale are now being developed that can economically process enormous amounts of animal waste.

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