Studies on the relationships between earthworms and soil fertility; some effects of earthworms on soil structure

The weight of wormcasts thrown on to the surface of eight fields of differing agricultural history depends on the numbers of Allolobophora longa Ude and A. nocturna Evans present and also on the mean size of the individuals of these two species. The weight of wormcasts produced per acre per annum on the different fields varied from 1 to 25 tons and it is calculated that from 4 to 36 tons of soil per acre per annum pass through the alimentary tracts of the total population of earthworms present. The percentage pore space of a soil containing a high population of wormcasting species is much greater than that of a field with a high population of worms which do not produce wormcasts. In two old pastures, the amount of coarse sand relative to silt and clay was found to increase appreciably with depth: this distribution is probably a result of the long-continued activity of earthworms.