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Ever had issues in establishing vegetation for slope stabilization or erosion control? Was it due to poor soil conditions, lack of rainfall or irrigation, washing of hydroseed during rainfall-runoff events prior to grass establishment, or competition from invasive weeds preventing your grass from establishing in a timely manner? Accepted to the USEPA’s national menu of best management practices (BMPs) and the American Association of State Highway Transportation Officials, compost erosion control blankets (CECBs) may just be the ultimate vegetation establishment tool in your erosion control tool box.

What makes the compost erosion control blanket different from other vegetation establishment tools? How do CECBs establish and permanently sustain vegetation over conventional means? CECBs are a one-step application BMP that provides: 1) immediate erosion control by protecting the soil from splash erosion and reducing sediment runoff transport by absorbing more rainfall than conventional erosion control technologies; 2) slow release nutrients for immediate and sustained vegetation growth even in nutrient poor soils; 3) pH buffering for optimum growing and nutrient availability conditions; 4) seed incorporation throughout the blanket profile; 5) an instant and optimum seed bed growing media for seed germination, establishment, and long-term growth; 6) increased water-holding capacity and reduced soil surface water evaporation to increase plant survivability in dry conditions; 7) soil conditioning from organic matter addition to improve short- and long-term soil quality for sustained plant growth and health; 8) beneficial soil microbes that can add long-term structure and stability to the soil and make nutrients available to plants; 9) micronutrients essential to long-term soil quality and plant health; and 10) a physical blanket that prevents invasive weed establishment and competition.

Sound good? What does the research say? A study conducted at the University of Georgia and published in the Journal of Soil and Water Conservation compared the short- and long-term vegetation growth characteristics of CECBs and hydromulch used in slope stabilization applications (Faucette et al. 2006). The BMPs were applied in triplicate to Pacolet sandy clay loam field plots that had been cleared and graded to 10%. Seed selection followed Georgia Department of Transportation standard specifications for the geographical region and season of application. Vegetative grass and weed growth analysis for each field plot was performed at 3 months and 12 months. Analysis included the percentage of total vegetative (grass + weeds) cover, total number of weed plants and different species, and aboveground biomass of the vegetation. Grass and weed biomass analysis was conducted only at the end of the study. Weeds were defined as any species other than the grass species that was specified (common Bermuda) (Faucette et al. 2006).

Percent Cover
After three months, the CECB treatments averaged 2.75 times more vegetation cover than the hydromulch treatments. Although the control was not seeded, there was no statistical difference between the control and the hydromulch treatments. Prior to plant establishment, it was likely that a greater proportion of seed washed down the slope during rainfall events in the hydromulch treatments. Percent cover results for all treatments at three months were lower than expected due to drought conditions over the three-month time period (90.7 mm of rain). The greater percent cover observed on the CECB treatments was likely due in part to their ability to hold more moisture (or restrict evaporation) than the hydromulch. This can be critical to plant growth during periods of drought, as experienced during the three months leading up to the vegetation analysis (Faucette et al. 2006).

Aboveground Biomass
Above ground biomass samples were harvested in May 2003, 12 months after the BMPs were applied. Although there were no differences between BMPs for biomass of Bermuda grass, weed biomass was 6.5 times higher in the hydromulch treatments relative to the CECB treatments, and 3.5 times higher than the control (Faucette et al. 2006). In a similar experiment conducted by Iowa State University, Richard et al. (2002) reported that seeded CECBs had significantly less weed biomass than seeded topsoil or bare soil. The slow establishment of the bermuda grass on hydromulched plots, relative to the CECB plots, may have enabled more weeds to establish and proliferate. Additionally, the 1.5 in CECB acted as a physical mulch layer, thereby suppressing and preventing potential weed seeds in the soil from emerging. This provides evidence that CECBs may suppress weed growth, relative to other slope stabilization and vegetation establishment BMPs (Faucette et al. 2006).

The study also found a strong positive correlation with mineral nitrogen (NH4-N and NO3-N) content in the BMPs and weed growth and proliferation within these plots, and although not directly tested in this study, it may further explain why the hydromulched plots had significantly more weed growth than the bare soil, as nitrogen supplied by hydroseed/hydromulch is typically from mineral fertilizers (Faucette et al. 2006).

On sites were vegetation has been cleared mechanically or from fire damage, where soils have been disturbed or are of poor quality and therefore are prone to soil erosion, CECBs may be the best one-step sustainable solution in your erosion control and vegetation establishment toolbox. As this study demonstrates CECB applications can provide a greater vegetation cover and less invasive weed growth where vegetation establishment is required or a may be a significant challenge. Additionally, if exotic or invasive weeds in ecologically sensitive landscapes or regions are a concern, soil quality is a problem, drought-prone conditions are likely, or irrigation equipment is lacking, long-term vegetation sustainability is a must, and a one-step, one-time application is a plus.

Soil Quality
So how does a BMP affect soil quality although it is applied only to the soil surface (e.g., not incorporated)? What have soil scientists been telling us for decades? The key to sustaining vegetation and reducing soil erosion is by managing organic matter (usually increasing it). Nature has been telling us the same story for millions of years. The benefits to increasing soil organic matter and its subsequent effect on reducing soil erosion are enormous. First the benefits to soils: increased porosity, increased aeration, increased fertility, increased beneficial soil microbes, increased nutrient cycling and availability to plants, increased aggregate stability, and more resilient soil ecosystems. All of these components work together to make soil more stabile and less erodible from the destructive actions of raindrops and surface runoff. They also work together to reduce runoff, thereby preventing the destructive force of runoff prior to commencement and reducing the sediment load potentially reaching a sensitive surface water body. However, it is no secret that the key to sustaining healthy vegetation is to create a healthy soil. Soil organic matter provides increased aeration, moisture, slow release of nutrients, habitat and food source for beneficial microbes, and a solid physical anchoring environment for both young and mature plant roots, enabling them to better withstand the tractive force of sheet runoff while simultaneously holding the soil in place.

What erosion control tool provides the most organic matter on the market? Compost blankets, period. Federal and state standard specifications for compost erosion control blankets call for an application of approximately 200 cubic yards (100 tons) per acre. Compost blankets are approximately 50% organic matter (dry weight), which equates to approximately 25 tons of organic matter per acre. What other erosion control tool on the market supplies this amount of organic matter? None.

The Journal of Soil and Water Conservation article reported that surface-applied (not incorporated) compost blankets, used for erosion control, increased the underlying soil organic matter between 0.02 and 1.10 g/kg of soil, while hydromulched field plots actually showed a reduction in soil organic matter (-0.04 to -0.1 g/mg) 18 months after application. Scientists reported that the increase in organic matter from compost blankets was likely due to natural incorporation from microbial migration, whereas, with hydromulch organic matter was breaking down faster than the natural replacement rate leading to a temporary decline in soil quality. Scientists also reported that microbial carbon in the soil (using extractable organic carbon as a surrogate) was on average 60% greater under the compost blankets relative to hydromulched soils. Soil microbes are responsible for cycling nutrients and making them slowly available for plants, increasing soil aggregates which reduce erosion, and are the foundation of a healthy soil and plant ecosystem that provides the functionality, stability, resiliency and sustainability to naturally manage construction and post-construction stormwater… and keep us from having to return. Compost blankets may be the only erosion control BMP on the market that has been studied on how it affects soil quality. Isn’t it time we included this in our decision making?