Soil-gas diffusivity and soil-moisture effects on N₂O emissions from intact pasture soils

Chamindu Deepagoda, TKK
Jayarathne, JRRN
Clough, Timothy
Thomas, S
Elberling, B
Journal Article
Fields of Research
ANZSRC::0503 Soil Sciences , ANZSRC::0703 Crop and Pasture Production
Grazed pastures are recognized as a dominant source of nitrous oxide (N₂O), a highly potent greenhouse gas. Studies have examined soil physical controls on N₂O emissions, including soil moisture status. Limited attempts to link N₂O emissions with soil-diffusivity (Dp/Do), using repacked soil cores, have shown peak N₂O emissions to align with a relatively narrow window of Dp/Do, despite a relatively wide range in water-filled pore space (WFPS), across a range of soil bulk densities. Such detailed studies have not been performed with intact soil cores. We investigated the effects of soil-water characteristic (SWC) and Dp/Do on N₂O emissions from intact soil samples, retrieved at three depths (0-5, 5-10, 10-15 cm) from three perennial pasture sites that received a KNO₃ solution (1800 mg, N mL-1). We observed distinct fingerprints of SWC and Dp/Do, which showed clear effects of soil structure on diffusion-controlled gas emissions. Depth-wise variation in soil moisture diminished as the soil was subjected to higher matric potential ( > ~ -100 kPa). Variation in Dp/Do, was more pronounced in the dry soil ( > ~ -1000 kPa), being largely constrained by soil moisture in wet soil (~ -100 kPa) with little depth-wise variation. Measured N₂O fluxes peaked within narrow ranges of WFPS and Dp/Do, 0.90-0.95 and 0.005-0.01, respectively. The value of Dp/Do can be determined using parametric models and presents a pasture management (e.g., irrigation, soil physical disturbance such as pasture renovation and animal treading)) tool to minimize N₂O emissions: soil Dp/Do should be maintained above a range of 0.005-0.01 to minimize N₂O emissions.
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