Preferential Transport of Nitrate through Soil Columns Containing Root Channels

Abstract

AbstractPreferential flow has been increasingly recognized as an important mechanism for water and solute transport. The objectives of this study were to characterize transport of NO3 through root channels in uniformly packed soil columns and to compare three commonly used solute transport models in describing NO3 transport through the soil‐root channel columns. Root channels were created by growing corn (Zea mays L.) or alfalfa (Medicago sativa L.) in 0.6‐m‐long soil columns. Transport of NO3 was then systematically studied with each of these macropore systems at a range of fluxes (from 0.042Ksm to 0.47Ksm, where Ksm is the saturated hydraulic conductivity of the macroporous system). A nonlinear least‐squares program was used to fit the convection‐dispersion equation (CDE), the physical nonequilibrium model (MIM) and a stochastic model (SM) to the experimental data. The results show that significant preferential movement of NO3 occurred in the decayed root channels at fluxes as low as 0.042Ksm. The MIM model provided a better description of the breakthrough curves than the CDE and the SM, while none of them were adequate to predict the preferential movement of the solute.