Ability of equilibrium and non-equilibrium models to simulate the effects of vermicompost and hydraulic conditions on nitrate and DOC leaching

Abstract

This study aims to model the effects of saturated−unsaturated flow rates and initial moisture content on nitrate and dissolved organic carbon (DOC) leaching in soils amended and unamended with vermicompost using equilibrium and non-equilibrium models. Flow rates ranging from 0.4 to 5.1 cm3/min were applied to the columns filled with the soils under initial saturated and air-dried conditions. The leaching of nitrate and DOC was simulated using a one-dimensional advection–dispersion model coupled with the equilibrium and non-equilibrium models. The accuracy of equilibrium without distribution coefficient (KD), equilibrium with KD, one-site, two-site and dual porosity models for modelling the nitrate leaching was 21.8, 33.6, 67.5, 82.2 and 83.9%, respectively, indicating the higher accuracy of dual porosity and two-site models compared to the other models. According to the results of the two-site model, the kinetic release was the most dominant process in all leaching experiments due to the fractions of equilibrium soil sites (F) < 0.5. Vermicompost decreased the diffusion coefficient (D0), distribution coefficient (KD), first-order rate constant (β) and retardation factor (RF). In comparison to the air-dried condition, the initial saturated condition compared to the air-dried condition resulted in less F and D0, higher KD and RF lower β for nitrate and lower KD and RF and higher β for DOC. Leaching using a desaturation flow rate of 0.4 cm3/min was more time-dependent, which reduced RF values from 22.6 to 1.09 and 21.5 to 3.68 for nitrate and DOC, respectively. Moreover, the desaturation flow rate reduced D0 and KD and increased β.