The Department of Soil, Water, & Climate has numerous studies on how worms affect properties of the soil. Worms incorporate a great deal of organic residue into the soil as well as create channels for air and water movement. The lab of Dr. Dennis Linden a former USDA/ARS scientist provided these slides about their worm study. They were looking at different tillage and residue management practices and their influence on worm populations.
Earthworms have a tremendous potential to ingest soil when populations are high. Soil ingested by worms is higher in nutrients and contains increased populations of microorganisms that continue to decompose the earthworm cast.
In order to study worm populations methods to count them have been developed. One method, as seen in the above picture, is to remove a soil core from the treatment area and count all the worms removed with the core. This method is time consuming and requires large equipment to pull our the soil core. The steel core method and hand-sorting only works for species such as A. tuberculata since they stay mostly in the top 12 inches of soil (and also baby nightcrawlers in good weather conditions, as well as the occasional adult nightcrawler who might be feeding or something at the time of sampling). The steel core method in general does not work well for nightcrawlers (L. terrestris) since they burrow 2 to 5 feet.
Another procedure is to bring the worms to the surface and count them. A mixture of mustard and flour is poured on the soil in a core. After a while, because the mixture irritates the worms, they come to the surface to get away from the mixture. This procedure leaves the soil intact and does not disturb the plot. After a while the worms are OK and can re-enter the soil in a different area outside the core. The mustard flour solution only works for species of earthworms that burrow vertically, like L. terrestris. It does not work for the worm species that do not create permanent vertical burrows, such as A. tuberculata. In this case it is fortunate for us that they burrow vertically.
Different treatments of tillage and residue left on the surface will develop different populations and species of worms.
Return to Unit Unit 9, Chapter 1
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