Rye cover crop incorporation and high watertable mitigate greenhouse gas emissions in cultivated peatland
Wen, Yuan | Zang, Huadong | Freeman, Benjamin | Ma, Qingxu | Chadwick, David R. | Jones, Davey L.
Drainage and cultivation of peat soils almost always result in rapid soil degradation and a loss of soil organic matter (SOM). Winter cover crop cultivation and subsequent incorporation and watertable elevation have been considered as potential strategies to improve soil quality and decrease nutrient loss in drained and cultivated peatlands. However, the combined effect of residue incorporation and watertable management on greenhouse gas (GHG) emissions in these highly productive fen peat soils remains unknown. In the present study, two winter cover crops with contrasting carbon/nitrogen ratios (vetch [Vicia sativa], 45–60; rye [Secale cereale], 13–14) were incorporated into peat soils as green manure (without extra synthetic/organic N addition) at two watertable depths (−50 and −30 cm). Our results showed that fast mineralization of incorporated residues can cause a large pulse of GHG release under favourable environmental conditions. Both vetch and rye incorporation increased CO₂ emissions compared with the bare soil treatments due to labile C addition and removal of N constraints. However, the two cover crops had strongly contrasting effects on N₂O emissions. Incorporation of low C/N ratio vetch stimulated N₂O emissions (average 21.8 ± 7.3 mg N m⁻² hr⁻¹) compared with the bare soil treatments, whereas high C/N ratio rye decreased N₂O emissions (average 0.09 ± 0.03 mg N m⁻² hr⁻¹). Raising the watertable slightly reduced CO₂ emissions from an average of 1.3 ± 0.4 (the bare soils) to 0.9 ± 0.3 g C m⁻² hr⁻¹ by inhibiting SOM mineralization but significantly increased N₂O emissions in the vetch treatments by stimulating denitrification. CH₄ fluxes were not affected by watertable depth, and their contribution to total global warming potential was negligible. Therefore, we conclude that high C/N ratio cover crops (e.g., rye) in combination with a raised watertable may represent a viable management option to mitigate GHG fluxes in fen peat soils.Show more [+] Less [-]