Surface alfalfa residue removal by earthworms Lumbricus terrestris L. in a no-till agroecosystem

Earthworm (Lumbricus terrestris L.) populations increase in alfalfa (Medicago sativa L.) and in no-till corn (Zea mays L.) fields compared to conventionally-tilled fields. The effects of earthworm activity on surface crop residue removal in no-till corn following alfalfa have not been studied. The main objective of this research was to measure earthworm effects on crop residue removal from the soil surface. Soils were Saybrook silt loams (fine-loamy, mixed, mesic Typic Argiudolls) on 2–9% slopes in south-central Wisconsin. We used a mesh-bag method to measure earthworm removal of alfalfa residue and the influence of forage quality on removal of residue from the soil surface. Coarse-mesh bags, with mesh openings 20 × 20 mm2, which allowed earthworms to remove alfalfa residues from the bags, had significantly greater alfalfa surface residue loss than fine-mesh bags with mesh openings 1 × 1 mm2, which prevented worms from removing residues. Forage quality of residues did not affect quantity of residue removed. We calculated that the observed populations of 40 to 60 L. terrestris m−2 could remove surface alfalfa residues at a rate that could account for the measured 122 g m−2 October to May biomass losses, given 60 days of suitable feeding weather and based on the measured loss rate of 69 g residue lost m−2 in 30 days. Potential residue removal by earthworms should be addressed in residue management strategies, especially where populations of L. terrestris are large and where crop residues are palatable to earthworms.