Cover crop residue influence on soil N2O and CO2 emissions under wetting‐drying intensities: An incubation study

Abstract

AbstractUnder increasing frequency and intensity of extreme weather events, the natural wet‐dry cycles of different intensities can induce soil carbon (C) and nitrogen (N) transformation and may contribute to increased nitrous oxide (N2O) and carbon dioxide (CO2) emissions from cultivated soils. While cover crop residue addition is a viable strategy to improve soil health, their impacts on soil greenhouse gas (GHG) emissions, especially N2O emissions, in response to wetting‐drying intensities have received limited attention. A 3‐factorial laboratory incubation was conducted using soils from a long‐term experiment to examine cover crop residue roles on N2O and CO2 emissions when exposed to different intensities of wetting‐drying cycles. These factors included (i) cover crop residue (3 levels): no cover crop, winter wheat (Triticum aestivum L.), and crimson clover (Trifolium incarnatum L.), (ii) wetting intensity (2 levels): 70% and 90% water‐filled pore space (WFPS), and (iii) drying intensity (2 levels): 10% and 40% WFPS. All treatments received the same amount of N fertiliser as urea equivalent to 100 kg N ha−1. We measured N2O and CO2 fluxes, N2O isotopomer composition, as well as dynamics of soil WFPS and biogeochemical changes after wetting. While cover crop residue addition generally exhibited higher CO2 emissions than the no cover crop treatment under all wetting‐drying intensities, their impact on N2O was more nuanced and contingent on cover crop residue type and wetting‐drying intensity. When wetted to 70% WFPS, crimson clover amended soils produced the largest daily and cumulative N2O emissions, whereas soil amended with winter wheat residues had comparable emissions to the no cover crop treatment. In contrast, cover crop residues, especially winter wheat, significantly decreased N2O emissions under extreme wetting to 90% WFPS which was often dominated by denitrification and nitrifier denitrification processes (except in winter wheat when wetted from 10% WFPS). Our results suggest that winter wheat cover crop residues mixed with N fertiliser could provide reliable N2O mitigation benefits under variable soil moisture conditions.Highlights Cover crop effects on N2O emissions from soil with varied wetting‐drying intensities were studied Increased risks of N2O emissions with increasing intensity of wetting of dry soils Crimson clover produced higher N2O emissions than no cover crop when wetted to 70% WFPS Cover crops mixed with N fertiliser reduced N2O emissions than no cover crop when wetted to 90% WFPS