On the equivalence between laboratory and field estimates of soil water retention parameters and its implications for modeling oxygen diffusion in structured agricultural soils

Soil water retention parameters (SWRPs) are ubiquitously required in several hydrological and biogeochemical models to simulate water movement, contaminant fate and transport, and gas diffusion in soils. While SWRPs are typically measured in the lab, these measurements vary significantly from field‐based hydrology. Hence, using lab‐measured parameters to make field‐based decisions can result in large uncertainties in hydrological and biogeochemical fluxes. In this work, we identified the hydrologic conditions and scales at which the use of lab‐ and field‐based measurements of SWRPs and derived oxygen diffusivity are equivalent. We compared retention curves measured in the lab and field for Ultisols under corn plantation, and their impact on modeled gas diffusion through soils at two scales: the soil core scale and the field scale. Our results demonstrate that no retention parameters measured in the lab and field were equivalent at the core scale. However, all parameters except for saturated water content (45.36% in the lab vs. 21.58% in the field) were equivalent ( p < 0.05) when averaged at the field scale. We also found that oxygen diffusivity calculated using lab‐based SWRPs represented field conditions if moisture and scale are considered. Specifically, diffusivity calculated based on SWRPs measured in the lab was equivalent to the diffusivity calculated using field‐based SWRPs when averaged for the field scale under well‐drained conditions, but not at moisture contents greater than field capacity. At the core scale, equivalence was not observed for any moisture condition. Additionally, we also determined that the SWRP required to upscale diffusivity values to the field scale is linked to the parameter representing pore size distribution. The findings from this study provide guidance to the hydrological and biogeochemical modeling community for using lab‐measured SWRPs to make field‐based decisions.