3/9/2002

The Kentucky Post (Covington, KY);

By DAVID KOESTER

Earthworms are very important soil organisms that aid in the decomposition of plant litter, such as the thatch layer, and in the recycling of nutrients.

They help to break down and condition plant remnants in their gut.  Their tunnels in the soil also help oxygen and water to enter the soil more easily and their castings (waste) enrich it.

Earthworms may be viewed as pests because their burrows and castings create a roughened surface.

Also, since earthworms are a preferred food for moles, pesticides are sometimes applied to remove them so the moles will go elsewhere. There is no scientific evidence, though, that eliminating earthworms will reduce problems with moles.

Earthworms make significant contributions to a fertile, healthy soil.

Attempts to control them to reduce surface disruption can have severe consequences, especially in thatch build up.

Thatch is a layer of living and dead roots, stems and organic matter that accumulates at the soil surface. Thatch accumulates when the rate of decomposition is much lower than the rate of grass growth from the soil.

Use of certain fertilizers or pesticides may encourage an accumulation of thatch by increasing turf growth and/or killing beneficial organisms, such as earthworms.

Excessive thatch reduces penetration of water and other materials, like fertilizer.

It also encourages shallow grass roots which makes turf more susceptible to stress or pests. A heavy buildup of thatch can require expensive dethatching.

Earthworms break down the thatch and pull organic matter into the soil. They also mix large amounts of soil into the thatch layer. This aids in a more rapid breakdown of the layer by increasing microbial activity and enhances its propensities for growth of turf grass.

Earthworms are generally found in the top 12 to 18 inches of the soil because this is where food is most abundant.

The worm ingests soil and organic matter, which is swallowed and ground in the gizzard. The ejected material, castings, is used to line the burrow or deposited at the entrance.

Earthworm activity depends directly on soil moisture and temperature.

Earthworms become active when soil thaws in the spring and move deeper in late summer as the soil drys.

David K. Koester is Campbell County's extension agent for horticulture.