Comparison of models for predicting pore space indices and their relationships with CO2 and N2O fluxes in a corn–soybean field

Abstract

Several models predict soil pore space indices (the relative gas diffusion coefficient, Ds/Do and the pore tortuosity, τ), but information is lacking on which models predicted indices better relate to soil processes. We compared pore space indices’ predictive models based on air-filled porosity (fa) alone vs. models using air-filled porosity and total pore space (Φ) (fa + Φ). We also assessed the relationships between these indices and CO2 and N2O. The study was conducted from 2011 to 2014 on a silt loam soil at Lincoln University. Soil samples were collected at 0–10 and 10–20 cm depth and oven dried at 105 °C for 72 h. After drying, fa and Φ were calculated and later used in models for predicting Ds/Do and τ. CO2 and N2O were measured with a Shimadzu gas chromatograph (GC) and a photoacoustic gas analyzer (PSA). Results showed that Ds/Do predicted using fa alone (Marshall and Buckingham) was higher as compared with values predicted with models based on fa + Φ (Sallam et al., Millington, and Jin and Jury) (P < 0.001). However, values of τ predicted with models based on fa alone were lowest (P < 0.001). CO2 and N2O measured with GC better related with Ds/Do and τ.