Casts of Aporrectodea caliginosa (Savigny) and Lumbricus rubellus (Hoffmeister) differ in microbial activity, nutrient availability and aggregate stability

The microbial activity, nutrient availability and aggregate stability of casts of the endogeic earthworm, Aporrectodea caliginosa, and the epigeic species, Lumbricus rubellus, were compared with that of uningested soil. Casts were collected 48hours after introducing earthworms of each species to containers which were filled with 15cm of soil covered with a 5cm layer of decomposing lucerne hay. Microbial biomass C, flourescein diacetate hydrolysis rate, aggregate stability and hot water-extractable carbohydrates tended to be lower in casts than uningested soil while the reverse was the case for light fraction C, basal respiration, metabolic quotient, exchangeable NH4++- and NO3− - N, Olsen P and phosphate-extractable SO42–-S. Casts evidently contained a smaller, but more metabolically active, microbial community than soil. Values for all measured parameters were appreciable higher in casts of L. rubellus than those of A. caliginosa. This was attributed to the greater amounts of surface litter (lucerne hay) ingested by the former due to its epigeic habit.