The impact of soil heterogeneity and management practice on preferential flow

The preferential flow of water and solutes through soils is considered as one of the major processes, which carry the risk of polluting the most precious groundwater resources. Due to the high economic and social costs involved in mitigating the adverse effects on human health, there is a great concern about preventing groundwater pollution. Therefore, it is important to develop methods of increasing the accuracy in measuring and modelling preferential flow, which requires a thorough understanding of the factors affecting preferential flow and the extent of their contribution. This study investigates the effect of conventionally tilled (CT) and not-tilled (NT) soil management practices in the field and heterogeneities introduced by soil tongues formed at inter-soil horizon boundaries in the laboratory and a computer model on preferential flow.;The laboratory experiments were carried out using a physical model containing two artificial soil tongues constructed at the boundary of a layered soil profile. The lower layer consisted of coarse sand and the upper tonguing layer was constructed using fine sand. Results showed that water and solute are transported faster through the fine sand tongues compared to the inter-tongue zones of coarse sand. These results were accurately simulated by VS2DTI software package. Further simulations using VS2DTI revealed that the level of transport through soil tongues depends on the number of soil tongues, their spacing and distribution. Furthermore, it was determined that the shape of the soil tongue, its length, and width influence the rate of preferential flow and the volume of soil profile containing solutes.;Soil water content sensors were installed in each CT and NT plot across crop-rows under corn and soybean cultivation and data were analyzed over two temporal scales. The analysis of water content data obtained in eight columns down to a depth of 40 cm indicated that more short term (event based) preferential flow (pore-scale) occurs in NT plot compared to CT plot. The consistent patterns of mean relative difference (MRD) of water content over the consecutive non-growing seasons regardless of the crop grown during the growing season suggest that there could be long term preferential flow . pathways (Darcian scale) in both NT and CT plots.