Microbial Biomass and Nitrogen Cycling as Affected by A. Trapezoides in a Colorado Soil.

The earthworms of Colorado are non-native lumbricid species, but they are not widely distributed across the state and are generally absent in eastern Colorado, dryland agroecosystems.  Recently, interest has grown in utilizing earthworms in no-till, dryland soils to promote residue incorporation, alter soil structure and porosity for increased water infiltration during severe rains, and enhance microbial activities related to nutrient cycling.  However, very little is known about the ecology of earthworm and their influences on soil properties in Colorado.  Can endogeic earthworms survive in a low-organic matter, cultivated soil from eastern Colorado (Adena, Ustic Paleargid)?  Can earthworm survival be enhanced with biosolids additions?  Do earthworms affect microbial biomass and N cycling activities?  To help answer these questions, a 12 week laboratory incubation study was established to study the effects of a common endogeic earthworm  (Aporrectodea trapezoides) on soil microbial biomass and soil nitrogen cycling.  Soils, with and without A. trapezoides and/or biosolids, were destructively sampled at 1, 2, 4, 8, and 12 weeks.  During the 12 week study, all of the worms in the Adena soil survived, and the survival of the earthworms was not significantly affected by the addition of biosolids.  Presence of A. trapezoides significantly increased soil N mineralization and nitrification activities, but did not affect microbial biomass C.  At the onset increased nitrification activity (8 weeks into the incubation), we measured a corresponding reduction in soil pH,  an increase in total soil C, and increased availability of several plant  micronutrients.  We concluded that it is possible for A. trapezoides to survive in a low-organic matter Colorado soil under optimal moisture content, and that A. trapezoides can enhance inorganic N and perhaps micronutrient availability to plants through their interaction with the native microbial community.