Objective

The objectives of this study were to:

1. Examine the efficacy of using an erosion control treatment containing composted dairy manure for stabilization and revegetation of steep slopes.

2. Compare results of runoff volume and concentrations and loadings of physicochemical constituents from experimental plots amended with a DMC/woodchips blend (designated as erosion control compost or ECC) or inorganic fertilizer (IF) subjected to simulated intense rainfall under non-vegetated and vegetated conditions.

Treatments

1. Erosion Control Compost (ECC)
   A 1:1 (v:v) blend of DMC and woodchips applied on top of the soil as a 2-inch (5-cm) layer equivalent to 126 t/ac (91.1 t/ac DMC + 34.8 t/ac woodchips)

2. Inorganic Fertilizer (IF)
   Granular fertilizer hand broadcast and then lightly raked into the soil surface at rates of 100 lb N/ac (112 kg N/ha) as ammonium nitrate, 100 lb P2O5/ac (112 kg P2O5/ha) as triple superphosphate, and 100 lb K2O/ac (112 kg K2O/ha) as potassium chloride

Procedure

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Eight, 3 by 6-ft (0.9 by 1.8-m) plots were established on a custom built steel bed {9.1m (30ft) × 1.8m (6ft) × 228.6mm (9in) deep} divided with metal borders and lined with a 5 mil plastic tarp. At the downstream end of each plot, a triangular tray and a downspout were constructed to convey runoff to a sampling container.

Soil used to fill each divided metal bed (plot) was excavated from a constructed hillside at the Riverside campus in College Station, Texas, used by the Texas Transportation Institute (TTI) for runoff studies. Three composite soil samples were collected for laboratory analysis. Soil texture was clay loam containing an average 27, 35 and 38 percent sand, silt, and clay, respectively.

After establishment of treatments (application of ECC and IF with no incoporation), all plots were seeded on the same day with a Texas DOT recommended seed mix (tall fescue, wheat, oats) with the addition of ryegrass to ensure vegetation establishment. The mixture was broadcast and lightly raked into the surface of each plot. All plots were monitored for seed germination, moisture and insect management.

An indoor rainfall simulation facility owned and operated by TTI at Riverside campus was used to conduct rainfall simulations and runoff sampling experiments on non-vegetated and vegetated ECC and IF plots on September 26 and November 15, 2005, respectively

The indoor facility contains an oscillating rain rack, suspended 14 feet (4.3 m) above the test surface (ECC and IF plots) is equipped with drip emitters that produce 0.12 to 0.16 inch (3mm to 4mm) droplets to mimic a rainfall intensity of 3.5in/hr (88.9 mm/hr), which corresponds to a 25-yr return frequency of a 1-hr storm at the experimental site. Oscillation of the rack provides a randomized raindrop pattern for uniform coverage of treatment plots.

The steel bed with established treatements was hoisted under the rain rack at a 3:1 side slope to mimic road right-of-way. Tap water was used for both rainfall simulation events.

At the downstream end of each plot, a reinforced 2-inch diameter plastic hose was connected to the downspout of each plot to collect the first flush (first litre of runoff) and the subsequent total runoff for a period of 30 minutes following runoff initiation.

Sample collection procedures are described in detail in the materials and methods section of the Study Report.