Legume Residue Configuration Modulates Topsoil Moisture and Greenhouse Gas Emissions Under Contrasting Wetting Regimes in a No‐Till Fallow

ABSTRACT Crop residues provide agronomic and environmental benefits under no‐till systems, but decomposition can increase greenhouse gas emissions, particularly from legume residues. Rainfall events influence soil moisture and microbial activity, yet relatively little is known about how surface residue configurations modify greenhouse gas responses under contrasting wetting regimes. This study evaluated how standing, mulched, and removed mung bean ( Vigna radiata (L.) R. Wilczek) residues affected topsoil moisture dynamics and CO 2 and N 2 O emissions during a subtropical winter fallow. A randomised complete block experiment with four replications compared two simulated wetting regimes: weekly wetting as frequent small events (10 mm every 7 d) and 4‐weekly wetting as infrequent larger events (40 mm every 28 d). Weekly wetting resulted in 14% greater seasonal topsoil moisture within the monitored crop‐row zone and increased short‐term cumulative CO 2 ‐equivalent emissions by 30% relative to 4‐weekly wetting. Mulched residue retained more topsoil moisture than standing residue, particularly under 4‐weekly wetting, where residue‐attributed moisture retention under mulch was more than double that under standing residue. However, under weekly wetting, mulched residue produced 21% greater cumulative N 2 O emissions and greater residue‐attributed short‐term cumulative CO 2 ‐equivalent emissions than standing residue. Repeated‐measures analyses showed a significant residue configuration × wetting regime interaction for N 2 O flux. This interaction remained significant when the analysis was restricted to common post‐wetting sampling intervals and after excluding the natural‐rainfall response period. These findings show that greenhouse gas responses to surface legume residues depend on both residue configuration and wetting frequency, emphasising the importance of residue architecture and rainfall event characteristics in dryland no‐till systems.