Runoff and water quality from highway hillsides: Influence compost/mulch

•We measured erosion from highway embankments which received surface compost/mulch.•Regardless of its thickness, mulch decreased erosion and phosphorus losses.•Light tillage reduced mulch effectiveness on erosion and should be avoided.•Incorporation of residue with surface soil is not recommended due to increased runoff.

Rainfall simulation experiments were carried out to quantify the effectiveness of surface compost/mulch placed on highway embankments on runoff and soil and nutrient losses. Six of eight plots received either 5 or 10 cm thick surface compost/mulch. The plots were located in two highway locations; one in an active highway construction area on US 61, and another in an established area with continual rill and sheet erosion on I-49, West Feliciana and Rapides Parishes, Louisiana, respectively. A Tlaloc 3000 rainfall simulator at an intensity of 70–80 mm h−1 was used for the runoff experiments. Two consecutive pulses of 30 min durations were applied to each plot in 2011 and 2012. The presence of the compost/mulch resulted in a reduction of runoff flow rates from a high of 1.3 mm min−1 to a low of 0.4 mm min−1. The cumulative runoff losses as a percentage of the applied rainfall was 90% for a tilled plot (control) which was reduced to 28% in an adjacent plot having 10 cm compost/mulch. Regardless of their thickness, light tillage and incorporation of the compost/mulch reduced its effectiveness and increased runoff and soil losses. The antecedent soil moisture content during 2011 and 2012 seasons were distinctly different. Nevertheless, the presence of the compost/mulch provided similar runoff flow rates and soil losses for both years. We conclude that the presence of compost/mulch on the soil surface decreased runoff flow rate, soil and phosphate (P) losses and is recommended for highway embankment erosion control.