Physical properties of casts of the earthworm Aporrectodea rosea

Some physical properties of casts of the earthworm Aporrectodea rosea were examined and compared with the properties of aggregates from the bulk soil. Cast shape was quantified by three ratio methods and two mathematical spectra methods, using data obtained by two-dimensional scanning. Shapes were compared with previously published descriptions of "modexi". The tensile strength of dry casts was measured by the indirect tension method and was found to be approximately 2.5 times greater than that of dried aggregates of similar size. Tensile strengths are used to predict that beds of casts are less compactable than beds of aggregates. From relationships between soil water content, matric potential and undrained shear strength of fresh earthworm casts, the mean pressure applied to soil as it is remoulded by passing through the earthworm gut is estimated to be 259 Pa.