RX for Soil
Just as you would treat a badly skinned knee—washing it, applying an antibiotic and covering it, the earth needs mending after it’s been disturbed and injured. Your untreated knee might get infected without attention, and disturbed soil will struggle to support vegetation without treatment. But instead of ointments, your prescription will include soil amendments.
A soil amendment is any material that, when mixed into a soil, will improve its physical properties. By using amendments on disturbed topsoil or subsoil, it’s possible to restore its vitality, so it can again perform its intended function. The goal of soil amendments is to recreate an environment that supports healthy plant growth. Ultimately, they work to reestablish the biological processes that sustain vegetation and continue to improve the integrity of the soil and rebuild a healthy layer of topsoil.
This kind of success is made possible by advances in the soil sciences. The industry has moved far past chemicalbased fertilizers and mulch. Today, there are biological and chemical additives that work to truly ‘amend’ deficient soils, actually changing its structure. This is done by restoring a vital balance of organic and mineral matter, water, air and, when necessary, neutralizing pH levels.
What amendments you use, or even what goals you establish, will depend on factors that are specific to each site. What are the preexisting conditions of the remaining soil? What is the level of disturbance? Do you have to bring in additional soil? If you do, what is the condition of the transported soil? In some instances, there will be toxicities; in others, there might be deficiencies that will limit the soil’s viability. Even the climate surrounding the site can influence what is required to support plant growth.
For example, in an arid environment, the soil’s ability to maintain and most efficiently utilize available water is a factor to consider. In sandy soils, many times water and nutrients drain too quickly to support root structures. Traditionally, organic amendments that are well decomposed, like composts, peat or aged manures, have been used to increase the soil’s ability to hold moisture and store nutrients.
On the other hand, clay-heavy soils are problematic, because clay absorbs and holds water. This leads to drainage problems and leaves plant roots gasping for air. In these instances, improved soil aggregation, increased aeration and drainage are all necessary. Conventionally, fibrous amendments like peat, wood chips, tree bark or straw, have been considered to be most effective in these situations.
Yet, there can be disadvantages to using such traditional solutions. “These types of amendments can be all over the board, sort of arbitrary,” explains Barry Cook of Northwest Hydromulchers Inc., in Boring, Oregon. “They can also have weed contaminants, or viable seeds.” He believes that today’s manufactured amendments are superior because explicit labels and clear product specifications reduce guesswork, and thus ensure successful outcomes.
Many consider the amendments that are on the market today to be safer and more efficient than amendments of the past. “With this new class of biotic soil amendments, we know exactly what’s in there. We know exactly how much to use per acre, and that it is clean,” explains Cook.
Selecting a soil amendment will depend on a combination of project goals, and site conditions. Soil texture, salinity, and pH are factors that may or may not require treatment. There are amendments that decompose rapidly for a fast improvement, to address seed germination; others that provide longer-lasting improvements by more slowly decomposing. You may choose a combination of both, depending on the site.
Because there are so many variables to consider, soil testing is often recommended before you start a project. Matthew Welch, technical manager at Profile Products LLC, in Buffalo Grove, Illinois, says his company always recommends testing to ensure plant growth. “You need to know what issues need to be addressed.” Testing will demonstrate the soil pH, micro and macro nutrients levels and salt levels. This allows you to determine exactly what deficiencies or toxicities exist.
A common problem of an unbalanced pH level will hamper the release of nutrients into the plants’ root zones. A pH level below 6 is far too acidic and would require the use of lime to bring it up, while a pH level above 7.5 needs to be brought down with the application of sulfur or gypsum. Through the use of such soil neutralizers, you can bring the soil into the ideal range for plant germination.
Other amendments are those that address electrical connectivity, dissolve salts, and organic matter issues, according to technical development manager, Michael D. Robeson, PhD, of Profile Products. “All of these issues can be addressed with different amendments.”
An additional classification of soil amendments are biological stimulants. These improve moisture infiltration to the soil, promote faster nutrient uptake by the plant, and provide better hormonal plant response to help root development and keep nutrients from leaching into runoff. Not every biological stimulant will perform all of these features, but this classification of amendments is used to promote plant growth by improving these functions.
So working with soil amendments can improve physical properties, such as texture, tilth, and structure, ion exchange capacity, water-holding capacity, nutrientholding capacity, aeration and water infiltration. Additionally, they can adjust pH, add nutrient and mineral values, suppress soil microbes that could harm plants, and increase the soil microbe community that helps plants grow.
A newer type of soil amendment works by adding organic matter to the soil and is used as part of an entire package designed to address various needs and conditions. According to Robeson, ideal soil has about 25 percent air, 25 percent soil, and a certain amount of moisture and organic matter. An optimal percentage of organic matter is three to five percent. Over time, a plant’s nutrients are supplied by organic matter. By providing a high amount of organic matter, seeds are immediately supplied with a growing medium.
Stripped soil from a construction site has very little going for it, except some water. The pH will likely be too high or too low; organic matter will be low, as will nutrients. This is obviously a poor environment for plant establishment or growth. By adding amendments that have been chosen to address site-specific issues, that also contain organic matter, seeds are provided with an optimum growing environment for germination. Then, once the seeds start growing, an entire biological process is kickstarted. Seeds slough off their outer shell, which creates more organic matter. This will support a root system that can tap into the soil substrate. Eventually, what was initially stripped dirt becomes healthy, sustainable topsoil.
At heavy construction sites, you are typically going to need a biotic amendment. On these sites, there is often not any topsoil left. And even when the original topsoil has been stockpiled, it has deteriorated significantly. “One of the issues we’ve seen is that biotic components in stockpiled soil don’t survive unless they are within the top four inches of that pile,” explains Welch.
Today’s manufactured biotic soil amendments often contain the new generation of organic matter. Additionally, according to Cook, an exciting advancement for these amendments is that they can be hydraulically applied. Using water as an application medium rather than mechanical means provides numerous benefits, and can increase success.
In addition to biotic soil amendments, there are also chemical amendments. These days, companies are working with chemicals in innovative ways to create a variety of soil products. Soil conditioners are available that work to break down the density of heavy soils, to help water penetrate into the soil’s root zone. There are also calcium chloride products that help amend soil with high sodium levels. Too much sodium is toxic to plants; calcium chloride moves some of this sodium out. It can also loosen the structure of the soil.
Traditionally, chemical-based soil amendments have been used most often to correct specific problems, such as unbalanced pH or toxic salts, while biotic amendments have been used to provide an overall healthier environment that ensures germination and vitality. Today, the distinctions are not so clear.
An example of this is a classification of soil amendments that isn’t technically a biotic amendment, but acts instead as a biotic stimulant. These contain some biotic and some chemical components. These types of products can offer both shortand long-term solutions.
Recent research has also been focusing on the use of different synthetic polymers and biopolymers for arid and semi-arid soil. The use of polymers as a soil-stabilizer additive has expanded significantly to control soil degradation and desertification. These are super-absorbent polymer-coated sand products used as straight additives, for increased moisture retention and plant growth. Soils treated with these additives, depending on preexisting factors and climate conditions, can retain adequate moisture levels even when the water supply has been dramatically reduced. This sand-like product can be used in addition to other amendments for drought-prone climates, or any time reduced water use is desired or required.
Amending soil is usually distinguished from mulching. Though decomposed mulches can be used as amendments, it is typically used to cover whatever seed, amendments and fertilizers have been laid down. While mulch is used to reduce evaporation and runoff, inhibit weed growth and moderate soil temperature, soil amendments are designed to alter the soil for sustainable plant and vegetation establishment, and to make subsoil at a disturbed site more like topsoil.
Agents used for short-term germination include humic acid, to increase the intake of nutrients and provide oxygen; seaweed extract, to trigger a hormonal response in plants and increase germination; and soil penetration agents to increase water infiltration on compacted or clay soil.
Long-term solutions include slow-release, coded nitrogen that is released over an extended period of time, typically between nine and 17 months, depending on soil conditions and climate. These products often contain endomycorrhizae, which adheres to plant roots to start the nitrogen cycle and increase water and nutrient uptake. Often, a combination of short- and long-term amendments are used.
Today, more than ever, you want to avoid post applications. You want to ensure that establishment requirements are met the first time. Because it’s your job to ensure strong establishment and even growth, analyzing the condition of preexisting soil and treating any deficiency or imbalance is a must. By using soil amendments, you can enrich your growing medium, supply seeds and plants with the nutrients they need, give them the ability to utilize these nutrients, and ensure the recreation of biological processes that create rich topsoil. Consider soil amendments an insurance policy and an invaluable tool for success.