Residue incorporation depth is a controlling factor of earthworm-induced nitrous oxide emissions.

Earthworms can increase nitrous oxide ( N2O) emissions, particularly in no-tillage systems where earthworms are abundant. Here, we study the effect of residue incorporation depth on earthworm-induced N2O emissions. We hypothesized that cumulative N2O emissions decrease with residue incorporation depth, because (i) increased water filled pore space ( WFPS) in deeper soil layers leads to higher denitrification rates as well as more complete denitrification; and (ii) the longer upward diffusion path increases N2O reduction to N2. Two 84-day laboratory mesocosm experiments were conducted. First, we manually incorporated maize ( Z ea mays L.) residue at different soil depths (incorporation experiment). Second, 13C-enriched maize residue was applied to the soil surface and anecic species L umbricus terrestris ( L.) and epigeic species L umbricus rubellus ( Hoffmeister) were confined to different soil depths (earthworm experiment). Residue incorporation depth affected cumulative N2O emissions in both experiments ( P < 0.001). In the incorporation experiment, N2O emissions decreased from 4.91 mg N2O-N kg−1 soil (surface application) to 2.71 mg N2O-N kg−1 soil (40-50 cm incorporation). In the earthworm experiment, N2O emissions from L . terrestris decreased from 3.87 mg N2O-N kg−1 soil (confined to 0-10 cm) to 2.01 mg N2O-N kg−1 soil (confined to 0-30 cm). Both experimental setups resulted in dissimilar WFPS profiles that affected N2O dynamics. We also found significant differences in residue C recovery in soil organic matter between L . terrestris (28-41%) and L . rubellus (56%). We conclude that (i) N2O emissions decrease with residue incorporation depth, although this effect was complicated by dissimilar WFPS profiles; and (ii) larger residue C incorporation by L . rubellus than L . terrestris indicates that earthworm species differ in their C stabilization potential. Our findings underline the importance of studying earthworm diversity in the context of greenhouse gas emissions from agro-ecosystems. [ABSTRACT FROM AUTHOR]