THE CHEMICAL COMPOSITION OF EARTHWORM CASTS

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Abstract
Samples of earthworm casts and of unworked soil from several depths were collected from a cultivated field and from 4 forested areas and subjected to chemical and mechanical analyses. At the time of sampling, the field soil contained approx. 3 casts to the sq. ft., averaging 2 ounces each, or 16,000 lb. to the acre. In the field soil, casts contained less exchangeable H and a lower clay content than the 0 to 6-inch layer; but the casts had higher pH values and were higher in total and nitrate N, organic matter, total and exchangeable Ca, exchangeable K and Mg, available P, base capacity, base saturation, and moisture equivalent. Total Mg was about equal in all samples. Forest soil samples showed similar but even more striking results. Forest soil casts were higher in N, organic C, and exchangeable Ca, and had a higher moisture equivalent than the casts from the field soil. These changes in composition as the results of earthworm activity are due chiefly to the intimate mixing of plant and animal remains with mineral soil in the digestive tract of the worm and to the action of digestive secretions on the mixture. That earthworms are beneficial to the soil has been established. Conditions favorable to the worms, however, are at the same time favorable to plant growth, and quantitative measurements under field conditions of the part the worms play in crop production have not as yet been obtained.

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