Effects of Earthworms on Nitrogen Cycling Processes and Decomposer Community Structure in Organic-based and Conventional Agroecosystems

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Earthworms affect many basic soil processes, but the overall impact of these important invertebrates on ecosystem-level processes are poorly understood. Drs. Stinner, Blair and Edwards suggest that earthworms are key organisms affecting the structure and function of decomposer communities and soil processes in many terrestrial ecosystems, including agroecosystems. This research examines the importance of earthworms as regulators of decomposer community structure, organic matter decomposition and N cycling in agroecosystems based on organic or inorganic sources of nutrients. Earthworm populations in field enclosures will be manipulated in three experimental agroecosystems where N is supplied primarily as i) legume-derived N, ii) animal manure N, or iii) inorganic fertilizer. Organic matter decomposition and N cycling processes will be used as integrating variables to assess the effects of earthworm activity on agroecosystem function. The following effects will be quantified: a) soil microbial numbers and activity, b) populations of other soil invertebrates, c) organic matter decomposition and changes in soil organic matter fractions, d) soil physical characteristics, e) partitions of N into selected above- and below-ground pools (plant biomass N, litter N, SOM , active (microbial) soil N, slow/passive soil N, extractable soil N); and f) rates and patterns of release of N from 15N-labelled plant residues, recovery in selected soil pools and plant uptake of N. This approach provides a unique, holistic perspective of the importance of earthworms in affecting ecosystem-level processes. Examining the effects of earthworms in systems based on organic inputs or inorganic N will provide data on the relative impact of earthworms in systems under different degrees of C or N limitation. Analysis of the interactive effects of earthworms and organic matter inputs on soil biota and processes will provide new insights into the basic mechanisms affecting N use efficiency and conservation in terrestrial ecosystems in general. The research will also contribute greatly to an understanding of regulation by earthworms of N dynamics in both organic N-based agroecosystems and conventional inorganically fertilized agroecosystems. The support and facilities for this research are outstanding.