Evaluation of Roadside Soil Compaction and Restoration Practices on Vegetation Growth and Water Quality

Abstract

The construction of roads using heavy equipment and cut-and-fill methods leads to heavily compacted roadside soils with low fertility, sparse vegetation, low water infiltration rates, and high erodibility. Poor post-construction vegetation and soil quality lead to higher runoff volumes with higher sediment and nutrient loads to local water bodies. Cost-effective methods are needed to restore roadside soils, establish sufficient vegetative cover, and maintain runoff water quality. A research project was undertaken to assess topsoil application, tillage, and yard waste compost amendment as means of restoring roadside soil quality. A 28-week pot study was used to test how topsoil depth, initial soil density, compaction from mowing equipment, and compost amendment influenced long-term soil density, hydraulic conductivity, and vegetation establishment. A 12-week mesocosm study with weekly simulated storm events was conducted to further examine the effects of soil type and soil bulk density on vegetation on a larger scale. Water quality testing of the simulated rainfall and runoff samples was also implemented to measure soil erosion and nutrient leaching. Compost-amended subsoil improved vegetation (biomass and grass heights) compared to subsoil, but it did not perform as well as topsoil. The yard waste compost was selected and applied at a rate designed to limit nitrogen and phosphorous losses, and it was successful, given that the compost-amended mesocosms did not export higher nutrient loads than mesocosms with inorganic fertilizer. Hydraulic conductivity was observed to primarily depend on soil density. A series of recommendations for highway projects to effectively restore roadside soil quality to improve vegetation and stormwater management are provided. A low-density layer of topsoil at least 20 cm deep is ideal. Yard waste compost should not be applied at a rate that raises soil organic matter by more than 2%.