Summary
This microcosm-based field experiment manipulated earthworm (Aporrectodea rosea) densities across three maize-tomato cropping systems—conventional (mineral fertiliser), organic (composted manure and legume cover crop), and low-input (alternating legume cover crop and mineral fertiliser)—using stable isotope tracers (13C and 15N) to track carbon and nitrogen incorporation into soil aggregates. Earthworm effects on C and N stabilisation in aggregates were management-dependent: in the low-input system, earthworms increased new carbon incorporation into microaggregates within macroaggregates by 35%, and new nitrogen in both coarse particulate organic matter and silt-clay fractions within macroaggregates by 49% and 38% respectively, whereas in the conventional system earthworms appeared to decrease nitrogen incorporation into free microaggregates and macroaggregates.
Regional applicability
The study uses a maize-tomato cropping system and North American earthworm species (Aporrectodea rosea), which differs from predominant UK arable rotations and native earthworm communities. However, the mechanistic findings regarding earthworm-mediated aggregate formation and nutrient stabilisation under differing management intensities are likely transferable to UK mixed and organic farming systems, particularly those incorporating legume cover crops or alternating management practices.
Key measures
Total carbon, 13C enrichment, total nitrogen, 15N enrichment in soil aggregates (macroaggregates >250 μm, microaggregates 53-250 μm, silt and clay <53 μm), and within-macroaggregate fractions (coarse particulate organic matter, microaggregates, silt and clay); earthworm population density manipulation
Outcomes reported
The study quantified how earthworm activity influences carbon and nitrogen incorporation into soil aggregates across three maize-tomato cropping systems varying in management intensity. Earthworm effects on aggregate-associated C and N dynamics were found to differ significantly depending on agroecosystem management approach.
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