Dirt, soil, seed support media: the material goes by lots of names. As kids, we play in it and track it onto our mothers’ clean floors. As erosion control specialists, we sometimes see it as a nuisance that must be contained or glued down. In revegetation projects, growth is the main goal, but the supporting soil is too often ignored.
Regardless of the way you see dirt or soil, its health should be a high-priority consideration for any project. The original state of the soil as well as its condition at the end of the construction phase have a strong impact on the success of a project.
“Vegetation equals Erosion Control” is a gold standard statement for the industry. But if you can’t get plant growth, your project is in trouble. Ongoing permit exceptions and having to schedule more inspections eat up profits quickly. If growth is not occurring or if the vegetation gets a good stand and then dies, the first place to look at is the soil.
Experts in soil testing and amendments agree that often soil tests are done only when problems crop up. Accomplishing the testing at the beginning of the project could save money and time: the earlier, the better when it comes to thinking about soil conditions and how to mitigate any issues.
Be Educated
Several of the experts who were contacted for this article stressed that education is the key to successful reclamation or revegetation of any site. H2 Enterprises and Duraroot Environmental Consulting of Keenesburg, CO, host the USA Reclamation Summit every year to provide education and networking for people in the erosion control industry, governmental entities, and contractors. Rhett Kerby of Bamert Seed Company says that in his job as sales and marketing manager, he spends much more time than he would have expected in educating clients. However, he thinks that the trend is toward better understanding of soil and how it can affect the successful completion of any project.
One important item to know is that you must have different expectations for different climates. Dr. Robert Schindelbeck of the Cornell University School of Integrative Plant Science notes that many projects use rules of thumb to prevent or mitigate problem soils. “In forg
Cottage Hills site, March 2014
iving locations or favorable weather conditions, these one-size-fits-all approaches can work,” he says.
Kerby works for a company located in west Texas, and as in most of the western US, the climate is arid to semi-arid. This climate is less forgiving and requires patience to see a full stand of vegetation, he says, and an understanding of soil conditions and the proper amendments is even more important in these drier areas.
Kerby says that the breakpoint in terms of rainfall seems to be about 25 inches annually. If your site is getting that much, the rain will slowly leach sodium out of the soil. The pH of rainfall is about 5 to 6, so over time it will also partially neutralize alkaline soils. But in arid and semi-arid regions, the rainfall amounts are not enough to show soil health improvement. Even sites that have been properly tested, amended, and seeded may take longer to show vibrant vegetation. It might take as long as 150 days or two growing seasons to reach full and ongoing growth. Patience is required.
Dos and Don’ts
Soil testing is not expensive, but if done improperly it can eat up profits. Soil amendments can add significant costs. If the wrong substances are added, the money
is wasted.
Aaron DeJoia of Duraroot Environmental Consulting describes the process. “Erosion control begins prior to any earthmoving activities and continues throughout the process, and the most effective erosion control is vegetation. The most important aspect of any erosion control soil testing procedure is a baseline assessment of the soil conditions.” He recommends seeking out certified professional soil specialists.
Here are a few dos and don’ts for testing and determining what soil amendments to use.
- Conduct soil testing properly.
- Use a reputable soil testing lab to perform the needed tests.
- Have a plan for topsoil salvage early in the construction process.
- Make sure that the amendments that are added are really what the site needs.
- Buy the amendments from a company that knows the business.
- Choose the right seed for the site, using expert advice as needed.
One of the most important parts of soil testing is obtaining representative samples. Soil should be collected from different parts of the site and at a variety of depths. You shouldn’t rely totally on USDA-NRCS soil maps, says DeJoia. “These soil maps are a wonderful asset, but they were never designed for use at the scale most erosion control and revegetation plans are prepared.” The maps should be consulted, but they are not the final indication of soil health.
Soil labs that will do testing are located across the country. Some are attached to universities, and others are independently owned. The costs can range from $35 to $110.
At construction sites, good topsoil is often scraped away and piled at the edge of the site. There it sits for the weeks or months of construction. During this time, the health of even good dirt declines. The nutrients and microbes can be baked or washed out of the soil. Have a plan to keep the soil healthy before the first bulldozer moves.
In years past, the most common measures of soil health that were tested were chemical: pH, salinity, conductivity, and presence of elements such as potassium and phosphorus. Those measures are critical, but they are not the only factors for soil health. Physical and biological criteria should also be tested.
Physical Characteristics
People working in the field of erosion control sometimes think they can eyeball a site and understand the physical condition. Some elements are easily seen. If you observe rilling or sediment in nearby waterbodies, that points to erosion problems. Cracking, crusting, and compaction are issues that can be observed. However, other factors must be considered. What is the extent of compaction? What is the soil texture, from clays to sands? What is the water-holding capacity and infiltration rate? How deep is the topsoil?
Clay soils are especially prone to compaction, and heavy truck traffic tends to cause compaction. This leads to soils that do not drain water easily and become waterlogged, killing roots. Compacted soils lose air pockets, which makes plants less likely to grow. Roots cannot penetrate the dense layers easily, so plants that are placed often die quickly.
Chemical Characteristics
A big factor in the chemical health of any soil is the pH. Highly acidic or alkaline soils do not support growth. Either high or low pH causes elements such as nitrogen, potassium, phosphorus, zinc, and iron to be unavailable for feeding plants. Yellowish plants often point to a lack of iron and zinc. The elements may be present, but they may be bound tightly by alkaline soil and not useful for the plants. An ideal pH is between 6.3 and 7.3, right around the point of neutral.
Chemical soil health can also be affected by high levels of salts or carbonates. High salt levels are measured by electrical conductivity tests. A high electrical conductivity means that excess amounts of salts are present. Soils with a high carbonate level are alkaline and are more difficult to treat with chemicals to lower the pH.
Biological Characteristics
The biological health of a piece of land does not mean just how the roots behave. It includes microbiological organisms that are not seen but are critical for soil health. Bacteria, nematodes, arthropods, protozoa, fungi, even earthworms must be able to survive and thrive for successful vegetation of any site.
Bacteria and fungi decompose organic matter and produce a sticky substance that holds soil together. This improves the soil structure, allowing passage of air and water. Fungi, such as mycorrhizae, work symbiotically with plant roots. The fungi provide nutrients, especially phosphorus and potassium, while drawing energy from the roots. They also produce enzymes that work to make nitrogen available to plants.
Other species such as nematodes and earthworms need to be present and healthy in order for the soil to be healthy. For example, earthworms eat everything and leave nutrients behind.
All Together
It is easy to look at these characteristics—physical, chemical, biological—separately. However, they interact and must be working together to produce a healthy soil. For example, a heavily compacted soil will be low in microbes and organic material. Soils with either low or high pH will bind nutrients such as potassium, nitrogen, phosphorus, and iron and keep away them from roots.
Schindelbeck uses three circles to illustrate this concept: one for physical, one for chemical, and one for biological characteristics, with the overlapping center being good soil health. He says his lab stresses soil functionality in its assessments. The soil must have nutrients available to maintain salt balances and build plant structures. Microbial health must be good to produce good soil.
The lab at Cornell tests the physical environment for soil stability to water and air presence, water storage capacity, and root growth. Soil depth is also critical. Another set of tests determines the total organic matter, easily decomposed organic matter, protein levels in the organic matter, and organism activity (respiration) to show biological health.
Once an assessment is done, the lab produces a comprehensive assessment of soil health. Each aspect is vividly shown to be green, yellow, or red, so a person can quickly spot the trouble areas.
“Soil is living, breathing, and complicated,” says Kerby. Once the soil health is known, the next steps to improving the soil can be taken.
The type of soil testing needed can depend on location. DeJoia notes that all soil testing needs to include pH and texture. In the western US, electrical conductive and sodium adsorption ratio (SAR) testing is crucial, but for the eastern US he recommends, at minimum, testing buffer pH and levels of nitrogen, phosphorus, and potassium.
Choosing Amendments
Compost has been used to enhance soil for years. It is still a valid addition to most soils. It consists of partially decomposed organic matter. It buffers the soil, pulling both acidic and alkaline soils into the neutral range. Compost also helps with the physical characteristics of soil by binding clusters of soil and keeping it in place better. The addition of compost improves the soil’s ability to allow passage of water and air.
Compost also improves the biological health. Organisms in the soil such as earthworms, fungi, nematodes, and bacteria can feed on nutrients in the compost.
In recent years, engineered soil media have hit the market. Profile Products of Buffalo Grove, IL, manufactures a product called ProGanics Biotic Soil Media. When topsoil is gone or depleted, ProGanics can help the soil recover. The product is a mixture of recycled thermally refined bark and wood fibers with a blend of biopolymers, biochar, seaweed extract, humic acid, endomycorrhizae, and other ingredients blended together. It can be applied with hydroseeding equipment and can be mixed with seed, fertilizer, and other amendments. The amount of ProGanics applied can be adjusted to fit each site. Replacing topsoil is expensive; two tank loads of ProGanics can do the same work as 36 trucks of topsoil, leading to cost reductions in fuel and time.
Amendments to change the pH of a site include lime, sulfur, and gypsum. These can be incorporated into the soil or sprayed on.
Plants require carbon, hydrogen, and oxygen, which they get from air and water. But they also need other chemical elements, including nitrogen, phosphorus, and potassium. These three are the ingredients listed by percentage on fertilizer bags. Other micronutrients needed include calcium, magnesium, sulfur, iron, manganese, and zinc. Applications of these substances can be accomplished with the spreading of fertilizer.
Rocky Mountain Bio Products of Denver, CO, supplies BioSol, a byproduct of penicillin production. After the stock is fermented and the penicillin removed, the remaining mass is mycelium. It has a high organic content and is exceptional for growth of microorganisms that are beneficial for plants. The company also carries a mycorrhizae mixture that supports plant growth and resistance to disease or stress.
Seed Choices
The crowning glory of any revegetation project is plant growth. The right seed must be chosen for the site, planned use, and soil conditions. Daryle Bennett, sales manager for Granite Seed and Erosion Control, says the choice depends on the objectives of the owner or manager of the site, including intended land use, preferred plant types, and the site potential. Once those are determined, the cultivars that are best adapted for the region should be selected.
Kerby says that more and more sites are specified to be covered with native species. He recommends working with a qualified professional seeding contractor. “Revegetation and reclamation seeding companies ensure the decisions made during the planning process are executed correctly. Seed placement and good seed-to-soil contact is a must for the seed to germinate.” He adds, “Native seeds require specific equipment to achieve the required placement and soil contact. Therefore, make sure your contractor is comfortable and experienced with the objectives of your project.”
What Not to Do
DeJoia describes a reclamation project that had remained under a stormwater permit for three years. The landowner could not get vegetation to grow after the project was complete. Three growing seasons had passed without significant growth. Duraroot conducted soil testing and determined that the salinity was high. Soil amendments were recommended and applied. By the end of the next growing season, the grass stand was healthy and the stormwater permits were terminated.
Bennett sees the same issues in many places in the western United States. “The most frequent situation I’ve encountered is dealing with problematic soils in the West where no soil testing was done and topsoil was not salvaged or perhaps improperly salvaged and re-spread prior to seeding.” With no soil testing to show deficiencies, no soil amendments were added. “The seed mix was drilled, and the resulting stand was poor to very poor. The contractor gets hired again to reseed. Perhaps soil testing is done the second time around. But the owner or operator may or may not have the budget to amend soils as recommended or to the extent recommended.”
Salinity at an Oil Production Site
A landowner in Colorado was concerned about reclamation of an oil production site on his property. Duraroot Environmental Consulting assessed the site and collected soil samples. Soil testing showed high levels of SAR and electrical conductivity. The site would need amendments to support growth of vegetation.
Duraroot recommended the addition of elemental sulfur, gypsum, wood chips, and nitrogen. H2 Enterprises was contracted to perform the work. The soil amendments were added and mixed into the soil. Native grass species were seeded, and a full stand of vegetation resulted after one growing season. The Colorado Oil & Gas Conservation Commission released the site from temporary permits. The landowner was happy to have his land green with a good stand of grasses.
Denuded in Alabama
A 2.7-acre home development site near Tallassee, AL, had been foreclosed on. After years of desertion, the site was washing away. The Alabama Department of Environmental Management required the owner to do something to stop the problem.
Soil testing was conducted through Profile Products Soil Solution Software (PS3). It showed that the site would not be healthy for any vegetation without extensive improvement in soil health. A combination of products supplied by Profile was added: ProGanics Biotic Soil Media was applied with ProPlus, NeutraLime, BioPrime, and JumpStart. These soil neutralizers and growth stimulants were stabilized into the soil with ProMatrix Engineered Fiber Matrix, wheat straw, and Tornado Tack ST-1000.
The process began on March 25. After one month, 100% stabilization was achieved and plant growth was starting. By July, the site had well-established vegetation. Hunter Bruce, P.E., owner of SpreadRite LLC and contractor for the job, says, “There’s no way this site would be growing the way it is so far without ProGanics.”
A year later, the site is still showing the worth of soil testing and the right amendments. Even with 80 inches of rain over 14 months, the site is showing no erosion, but has thick, vibrant growth.
Texas Saltwater
Kerby consults on projects around Texas, including some for the oil and gas industry. This industry is changing its practice of dealing with a saltwater spill. Saltwater is used in fracking, and occasionally soil is contaminated by an accidental release. When the salt, sodium chloride, penetrates the soil, the sodium attaches fairly tightly to soil particles because soil carries a negative charge and the positive sodium is attracted to it. The chloride ion, with a negative charge, is repelled from the soil and the chloride migrates lower, possibly threatening groundwater.
Past practice was to dig up the soil as far down as the chloride has spread. The “dig and haul” practice involved completely replacing that soil before vegetation could be attempted. It was a very expensive process, involving a high cost for new topsoil as well as time and money for hauling.
Recently, the practice has changed. The soil is dug up and spread on large tarps with rubber backing. Water is slushed through the soil, leaching out the chloride. The water is captured and treated. The soil can now be replaced over the site.
There are still two problems after this process has been done. First, the topsoil and subsoil have been blended together. In addition, the sodium is still present. Both of these conditions can be treated with the proper amendments before seed is sowed. Amendments to improve the physical condition of the blended soil are used. And, because the presence of sodium raises the pH, applications of acid are used.
Learn and Do
Once you know and understand the benefits of soil testing and how to match amendments to the problems, your sites will see improved vegetation growth. Apply what you’ve learned or hire contractors who know the value of good soil and how to achieve the goal of a healthy soil foundation. You will never again look at dirt in exactly the same way. You will see it as a living, active, dynamic material that can, if needed, be treated to be the best support for any seed that you plant.