Environmental Considerations: A Proactive Approach to Site Revegetation
On construction projects worldwide, post-construction site stabilization often is an afterthought. With constant increases in water-quality laws and regulations—and the effect of stormwater pollution on the environment—it’s becoming more important to keep soil and nutrients onsite. Incorporating sustainable vegetation—the best erosion control available—is a proactive approach.
Not every architect or engineer who writes revegetation specifications has experience in agronomy or soil science. This is where many common mistakes are made while attempting to revegetate and closeout sites. There are certainly times when everything on a site is just right, and all that’s needed to establish vegetation is seed, fertilizer and a little bit of straw. However, this assumptive approach too often leads to revegetation and erosion issues as well as site violations.
Some of the most-frequent factors affecting site stabilization and revegetation can be addressed by having a soil laboratory analyze samples of the soils and substrates that need to be revegetated. This simple and relatively inexpensive step offers many benefits. It allows for proper vegetation selection, can prevent misapplications of common amendments such as fertilizers and agricultural lime, can decrease nutrient runoff, will prevent wasted applications on inhospitable sites, and ultimately allow contractors to set realistic expectations for revegetation.
Customized to Conditions
After the soil is tested and analyzed for soil pH, particle size (sand, silt and clay), soluble salts and sodium content, agronomists can more-accurately select a seed blend that will establish on the site’s substrates and achieve vegetation goals. Whether the issue is a physical quality, such as how well the soil will drain, or a chemical condition, such as high salt content, selecting vegetation adapted to a site can play a huge role in revegetation success and overall site sustainability.
Soil testing and analysis also allows for proper quantitative soil-amendment applications to develop a suitable growing media from less-than-desirable substrates. Adding amendments to the substrate to correct pH issues, increase infiltration or trigger seed germination can increase the agronomic potential of a substrate. Fertilizer recommendations also can be customized to maximize vegetation establishment. A few nutrients, primarily nitrogen and phosphorus, are very soluble and readily leach off sites. If a site is over fertilized, these nutrients can leach into water bodies and cause environmental and compliance issues. There are a few free services available that can help with soil testing and analysis, including <I>www.profileps3.com<I>. This soil-solution software requires a free user profile to be created and then allows users free access to soil testing and reports to help understand the substrate conditions on project sites.
Dealing with Deficiency
High percentages of construction sites can be classified as “soil deficient” or “dead soil.” These sites are difficult to sustainably amend, and there are basically two options: 1) haul in copious amounts of topsoil or 2) develop the organic soil horizon naturally. When hauling in topsoil, there are a few things to consider:
- What is the agronomic potential of the proposed soil?
- Is this topsoil consistent from truckload to truckload?
- How often is the topsoil tested to ensure quality?
- Is there a chance that invasive species or weed seeds are in the shipments?
- What’s the total cost of material, hauling and application?
- Will topsoil added to a slope increase erosion potential?
ProGanics Biotic Soil Media is an available Engineered Soil Media (ESM) that increases organic concentrations of deficient substrates and accelerates the development of these dead soils. ESMs are manufactured products, so they have many advantages. They’re extremely consistent, are phytosanitized to eliminate weed seeds and pathogens, can be applied quickly through hydroseeding equipment, and work well with Hydraulically-applied Erosion Control Products.
If there are no toxic elements to the soil, it’s likely that over long periods of time, the organic horizon will develop naturally. However, adding an ESM to a site will expedite the creation of the organic layer and begin a nutrient cycle that will lead to a more-sustainable stand of vegetation, typically leading to fewer fertilizer applications.
Occasionally, the substrate available onsite is toxic to vegetation. It’s extremely important to know this prior to any revegetation attempt. If revegetation is attempted in a toxic site, the entire cost of application often is a complete waste. Depending on what type of toxicity is plaguing the site, there may only be a couple of options for successful revegetation: 1) capping or excavating the toxic, nonviable material, followed by a topsoil application or 2) adding topsoil to buffer the root zone from the toxic substrate.
It’s difficult to predict potential project success using an assumptive approach method. Without a proper knowledge of soils or substrates onsite, there’s much left to chance. Utilizing laboratory testing and professionals who have been trained to analyze soils for agronomic potential is an inexpensive and valuable proactive approach to increase revegetation success.