Infiltration into vegetated stormwater control measures (SCMs) is critical for reducing stormwater runoff. Applying tillage to ameliorate compaction enhances vegetation establishment, increases infiltration, and reduces runoff. The long-term benefit of tillage as a BMP may be limited by soil reconsolidation with routine traffic and maintenance. Our research evaluated the sustainability of vegetated SCMs following tillage pre-treatment. We simulated post-construction soil conditions on both cut and fill slopes to examine the effects of applying tillage BMPs with and without compost amendments over periods of more than two years at five sites. Additionally, we evaluated tillage BMPs on two active roadways where we compared them to existing stands of grass for runoff reduction. Results from simulated post-construction sites suggest that benefits of tillage can be maintained for two years or more. Compared to controls, bulk density was reduced by an average of 11% for periods >24 months when tillage was applied. Infiltration rates averaged more than three times larger than controls after >24 months. No differences were observed in surface bulk density or infiltration rate based on depth of tillage (6 in vs. 12 in. [15 cm vs. 30 cm]). Compost addition affected infiltration rate in only one of four trials, and in this case mitigated the effect of mower traffic on tillage alone. In two other trials where mower traffic was tested, it had no effect on bulk density or infiltration rate. The two roadway sites differed from the other trials in that the control was established grass. Compared to established grass, tillage and tillage plus compost reduced runoff from natural rainfall by averages of 10 and 43%, respectively, over 18 or more runoff events at each site. At one site, runoff reduction compared to control appeared to diminish within a year of tillage (with or without compost). At the other site, reductions in runoff were mostly maintained throughout monitoring. At the end of monitoring, bulk density and infiltration rate were no different between control and tillage, but bulk density was lower and infiltration rate was higher for tillage with compost addition compared to control. These results suggest that, unless compost is incorporated with tillage, tillage benefits relative to existing grass stands will likely be short-term. Overall, results indicate that tillage BMPs can effectively reduce bulk density, increase porosity, and enhance infiltration for disturbed, new construction soils. Tillage BMPs may also be beneficial in locations which with known infiltration and grass stand issues.
