Erosion control with vegetation in highway corridors
Grading operations in highway corridors disturb the natural vegetation and land contours, thereby causing erosion and pollution. Minimizing erosion is predicated on the principle of maximizing water infiltration to reduce massive runoff of water. This depends on grading and soil preparation methods, augmented temporarily by mulches, but perfected by developing a vegetative cover quickly. The speed of developing a vegetative cover and shifts in plant biota to persistent covers depend on grading and subsoil preparation, soil amendments, mulches, and specially designed seed mix:tures for seeding at various seasons. The management of these factors, through plant succession, results in persistent vegetative covers of legumes like crownvetch (Coronilla varia L.) or sericea (Lespedeza cuneata G. Don.), requiring little or no mowing or fertilizer maintenance. In difficult environments or in adverse seeding seasons, multi-step seeding and fertilization is usually required.
Erosion from slopes with sparse grassy vegetative covers in highway corridors can be minimized or eliminated by overseeding with persistent legumes and the application of needed soil amendments.
Topsoiling is not needed nor recommended on properly graded subsoil materials with adequate lime and fertilization, especially when the final botanical component is a persistent legume. Soil moisture was higher and temperatures lower for rough graded subsoil as compared to roughened topsoil, providing a more favorable microenvironment for plant growth with subsoils. Stands and vegetative covers were similar, although weed growth on topsoil materials was more severe than on subsoils. Roughened topsoil or subsoil surfaces sharply enhanced growth and vegetative cover as compared to the smooth topsoil or glazed subsoil. This was attributed to better infiltration and higher soil moisture, allied with improved bulk density and porosity.
Twelve species of grasses and legumes were grouped into three categories according to total emergence. Perennial (Lolium perenne L.) and annual (L. multiflorum Lam.) ryegrasses, German millet (Setaria italica L.), redtop (Agrostis alba L.), and Abruzzi rye (Secale cereale L.) had the highest rate and total seedling emergence with maximum emergence obtained by day 6 under favorable moisture conditions. Crownvetch at 21 C, creeping red fescue (Festuca rubra L.), Kentucky bluegrass (Poa pratenses L.), Kentucky 31 fescue (Festuca arundinacea Schreb.), and weeping lovegrass (Eragrostis curvula Schrad. Nees.) at both temperatures. had intermediate rates and total emergence with maximum emergence obtained by day 8. Crownvetch at 28 C and sericea and common bermudagrass (Cynodon dactylon L.) at both temperatures had the slowest rates and least emergence, obtaining maximum emergence between days 10 and 13.