LEARN-TECH-AGR-CD-V01

This is output #4

ABSTRACT

Grazed pasture constitutes a major source of agriculturally derived nitrous oxide (N2O), a potent greenhouse gas. Soil texture and structure, soil moisture, and soil-gas diffusivity are considered to be major soil physical drivers controlling pastoral N2O emissions. Research gaps, however, still exist with regard to their combined roles on N2O emissions dynamics. This study used 2 mm-sieved and repacked soil samples, retrieved at three depths (0, 10, 15 cm) from three grazed pasture sites in New Zealand, to investigate the combined effects of soil-water characteristic (SWC) and soil-gas diffusivity on N2O emissions. The existing and modified parametric functions were used to numerically characterize and parameterize measured particle size distribution, SWC, and soil-gas diffusivity. We observed distinct particle size distributions within the three soils with little variation across depths.  Distinct fingerprints were observed for SWC and gas diffusivity in the three pasture soils, suggesting clear effects of soil type on diffusion-controlled gas emissions. The depth-wise variation of soil moisture above ~-10 kPa showed clear soil type effects. Soil-gas diffusivity, on the other hand, showed pronounced depth-wise variation below ~-1000 kPa. Pore tortuosity was found to be non-linearly correlated to air-filled pore space as well as the size distribution of particles. The measured N2O fluxes peaked around a diffusivity window of 0.005-0.01 for all soil types while the corresponding water-filled pore space ranged between 0.80 – 0.95.
