Evaluation of Mulch Application As An Erosion Retardant On Louisiana Roadsides.

Turbidity associated with total suspended solids (TSS) is considered the most problematic nonpoint source pollutant of Louisiana surface waters. With high annual precipitation in Louisiana, careful attention should be given to controlling the erosion on highway right of ways. Two locations were chosen for this study: 1) an active highway construction site in West Feliciana Parish along US Highway 61(two plots), and 2) an established right of way along IH-49 in Rapides Parish (six plots) which showed signs of continual rill and sheet erosion. Several variables were evaluated: 1) thickness of mulch coverage (treatments: control (no mulch), two, and four inches), 2) slope inclination (ranged from 10–34%), and 3) tillage incorporation of mulch (mulch was incorporated into the soil with a tiller at some sites, surface applied with no tillage at other sites). Soil moisture and soil temperature were recorded every 10 minutes via in-situ sensors in each of the plots. Runoff from precipitation events was channeled into standard H-flumes and collected via refrigerated ISCO autosamplers. Water samples were subjected to turbidity, TSS, biological oxygen demand (BOD), pH, and electrical conductivity (EC) analyses. The results indicated that the turbidity and TSS values were less when the mulch was applied on the soil surface. However, when light tillage was applied, turbidity and TSS increased compared to no-tillage plots for all mulch treatments. The worst erosion was realized under light tillage on a 25% slope with no mulch (control) coverage. Furthermore, despite variable slope inclination, the application of two inches mulch is recommended as both an effective and cost-minimized way for controlling erosive sediment runoff from Louisiana roadsides.