Establishment of Vegetation on Graded Road Cuts as Influenced by Topsoiling and Tillage

Abstract

Topsoil application along roadsides results in added expense, delays seeding newly constructed areas, and creates potential erosion sites when moisture and seedbed conditions may be optimum for germination and plant growth. Two experiments were conducted to compare establishment of vegetation on graded highway cuts. One was concluded on Groseclose subsoil near Blacksburg, Virginia, comparing surface application on NPK fertilizer and lime (L) on smooth (glazed) subsoil, on tilled subsoil before NPKL application, on tilled subsoil after NPKL application, and with surface application of NPKL to 15 cm of topsoil. Experiment 2 was conducted on Lenoir subsoil near Gloucester to compare a 15-cm layer of tilled topsoil to tilled subsoil, and smooth top soil to glazed subsoil. Each area was fertilized with NPK at rates of 168-146-139, 112-98-93, and 84-73-70 (kg/ha). Incorporated NPKL and roughened subsoils gave 8 and 11% better vegetative cover (about 0.3 more crownvetch (Coronilla varia L.) plants/dm2) than did 15 cm of topsoil over subsoil. Tilled topsoil or subsoil had about a fourfold better vegetative cover than when either was left smooth. Erosion was 50 and 25% as great on tilled topsoil and subsoil, respectively, than on either left smooth. Bulk density of smooth and roughened topsoil or subsoil ranged from 1.38 to 1.42 g/cm3 as compared to 1.76 g/cm3 for the compacted smooth subsoil. Likewise, total porosity was increased from 22 to 42% above glazed subsoil by roughening and use of topsoil. The altered physical properties created by roughening increased plant growth by increasing soil moisture content of the topsoil by 23% and that of the topsoil by 45% and by decreasing soil temperature. Tilled subsoils with adequate soil amendments can result in satisfactory plant covers similar to those obtained by topsoiling at a much lower cost.