Native earthworm population dominance after seven years of tillage, burning, and residue level management in a wheat-soybean, double-crop system

- Aporrectodea trapezoides and native Diplocardia sylvicola earthworms were identified.
- D. sylvicola was relatively more abundant than the introduced earthworm.
- Earthworm densities were relatively high for row-crop systems.
- Residue and burning interacted with tillage to influence earthworm densities.

Earthworm density is often reduced in low organic matter soils that are intensively managed for row-crop production, but earthworms can serve as a sensitive bioindicator of response to residue management. This study relates earthworm density and community composition to residue management after seven years of consistent management practices in a wheat (Triticum aestivum L.)-soybean (Glycine max (L.) Merr.), double-crop system in the Lower Mississippi River Valley delta region of eastern Arkansas. Residue management practices included conventional tillage (CT) and no-tillage (NT), N fertilization to produce HIGH and LOW wheat residue levels, and BURN compared to unburned (NO BURN) wheat residue remaining on the soil surface. Total mean earthworm densities ranged from 271 to 508 m−2 in the top 20 cm across treatments. Both exotic Aporrectodea trapezoides (Dugès) and native Diplocardia sylvicola Gates adult earthworms were present with little difference in diversity among sampled communities; however, more than 65% of adults were D. sylvicola in all treatments. Native, total, or juvenile earthworm densities in different treatment combinations were correlated to different soil properties, including pH, electrical conductivity, and Mehlich-III-K, Ca Mg, S, Cu, and Mn concentrations. Residue level and burning influenced total, juvenile, and native earthworm densities differently in CT and NT. Tillage presumably influenced earthworm density through effects of residue placement at the surface (NT) or within the soil profile (CT). Earthworm densities were greatest in the BURN-HIGH treatment combination under NT, which contrasted with greatest densities in the NO BURN-HIGH which did not differ from the BURN-LOW treatment under CT. Native earthworms predominated with a common exotic species in a wheat-soybean double-crop system in Arkansas where earthworm densities were dependent on the interaction of tillage with burning and fertilization to influence wheat residue amount. Differences in earthworm abundances may serve as a bioindicator of long-term sustainability of common residue management practices in the highly agriculturally productive delta region in the Lower Mississippi River Valley.