ABSTRACT (Words: 256) 
Density-induced soil structural changes may potentially alter soil total porosity, re-proportionate the size distribution of pores in the soil and thus change the soilâ??s water retention characteristics, gas diffusion and transport properties, and the emission of greenhouse gases. In this numerical study, we characterized and parameterized water retention, pore size distribution, gas diffusivity and cumulative emissions of nitrous oxide (N2O) and nitrogen (N2) fluxes in a differently compacted silt-loam sampled from a grazed pasture in Lincoln, New Zealand.  The soils used for the simulations were subjected to five different density treatments (1.1, 1.2, 1.3. 1.4, 1.5 Mgm-3), subsequently saturated and successively drained to 11 matric potentials at which water retention, gas diffusivity and flux measurements were carried out. Results show strong correlations between best-fit soil-water characteristic parameters and the density levels. A recent predictive gas diffusivity model developed for undisturbed soils was modified to better characterise the measured gas diffusivity data in sieved-repacked pasture soils. Further, two exponential and linear parametric models were developed to adequately parameterize the observed fingerprints of cumulative (35-day) N2O and N2 fluxes, respectively. Results clearly distinguished the density-induced changes in pore structure, pore size distribution, gas diffusivity and emission of gas fluxes and hence provide useful implications for pasture management to reduce future emission of greenhouse gases. Results particularly highlighted the importance of ensuring a diffusivity ? 0.038 in order to limit extensive emission of N2O and N2 fluxes. The improved parametric models and parameter correlations provide valuable numerical insight to better characterize density-dependent behaviour in soil physical properties and functions. 
