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.