Sep. 23, 2024
This chapter teaches people to:
Soil is a living, breathing, natural entity composed of solids, liquids, and gases. Soil has five major functions:
Our focus will be on the fifth function. In this role, soil provides structural stability for plants and retains and relinquishes water and the nutrients necessary for plant growth.
An ideal soil for plant growth contains 50% pore space and 50% solids, with the pore space filled with equal parts air and water. This distribution rarely occurs because pore space varies with soil texture and soil management. For example, tilling increases pore space, while poor drainage and compaction reduce it.
Soil solids are a blend of mineral materials and organic matter. The mineral materials are typically weathered rock of varying sizes called sand, silt, and clay. The organic matter consists of decaying plant and microbial residues. The relative amounts of pore space and mineral and organic matter vary greatly among different soil types. But for plant growth, most soil scientists agree that 50% pore space, 45% mineral matter, and 5% organic matter make up an ideal ratio. The distribution of solids and porespace in ideal, compacted, and poorly drained soils is illustrated in Figure 1-1a, Figure 1&#;1b, and Figure 1&#;1c.
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Print Image
Print Image
Most naturally occurring, undisturbed soils have three distinct layers of variable thicknesses. The layers are the topsoil, subsoil, and parent material. Each layer can have two or more sublayers called horizons. Collectively, the horizons make up the soil profile. The predominate parent material varies by location in North Carolina. In the NC piedmont and mountains, the parent material is typically weathered bedrock known as saprolite. In the river bottoms and stream terraces of the NC piedmont and mountains, the parent materials are the floodplain sediments delivered from upstream where erosion has occurred. In the NC coastal plain, the parent materials are marine sediments deposited over eons as the oceans go through the natural cycles of advance and retreat. In the easternmost NC coastal plain, the dominant parent material is organic matter. These organic soils are typically found in areas that just 50,000 years ago were below sea level. Such areas are swamps where plants grow and thrive. But these areas are too wet for the plant residues (leaves, branches, roots, trunks, and the like) to efficiently decompose.
Soils&#; properties vary with the soil depth. The surface soil, or topsoil layer (O and A horizon in Figure 1&#;2), usually contains less clay, but more organic matter and air, than the lower soil layers. Topsoil is usually more fertile than the other layers and has the greatest concentration of plant roots.
The subsurface layer (B and C horizon in Figure 1&#;2), known as subsoil, usually has a higher clay content and lower organic matter content than the topsoil.
Soil properties often limit the depth to which plant roots can penetrate. For example, roots will not grow through an impenetrable layer. That layer may be bedrock (Figure 1&#;3), compacted soil, or a chemical barrier, such as an acidic (very low) pH. A high water table can also restrict root growth due to poor soil aeration. Few big trees grow in shallow soils because big trees are unable to develop a root system strong enough to prevent them from toppling over. Shallow soils also tend to be more drought-prone because they hold less water and thus dry out faster than deeper soils. Water lost to runoff on shallow soils would instead be absorbed by a deeper soil. In addition, deep soils allow the roots to explore a greater volume, which means the roots can retain more water and plant nutrients.
Soils change in three dimensions. The first dimension is from the top to the bottom of the soil profile. The other two dimensions are north to south and east to west.
The practical meaning of this three-dimensional variability is that as you move across a state, a county, or even a field, the soils change. Five factors of soil formation account for this variation:
Differences in even one of these factors will result in a different soil type. Soils forming from different parent materials differ. Soils forming from the same parent material in varying climates differ. Soils at the top of a hill differ from soils at the bottom. The top of the hill loses material due to natural erosion; the bottom gains the material from above. Considering the number of possible combinations of these five factors, it is not surprising that more than 450 unique soil series are currently mapped in North Carolina. Globally, more than 20,000 different soil series occur. Neighborhood level soil series can be found by typing &#;Web Soil Survey&#; into any Internet search engine.
John A. Kelley, USDA NRCS, Flickr CC BY 2.0
John A. Kelley, USDA NRCS, Flickr CC BY 2.0
Print ImageJohn A. Kelley, USDA-NRCS, Flickr CC BY 2.0
John A. Kelley, USDA-NRCS, Flickr CC BY 2.0
Print ImageThere are strong relationships between soil physical properties and soil chemical properties. For example, surface area is directly related to chemical reactivity.
The negative ends of two magnets repel each other. The negative end of one magnet attracts the positive end of another magnet. This same principle affects the retention of plant nutrients in soil. Some plant nutrients are cations, which have a positive charge, and some are anions, which have a negative charge. Just like the opposite poles on magnets, cations will be attracted to anions.
Soil particles are similar to a magnet, attracting and retaining oppositely charged ions and holding them against the downward movement of water through the soil profile. The nutrients held by the soil in this manner are called &#;exchangeable cations&#; and can be displaced or exchanged only by other cations that take their place. Thus, the negative charge of a soil is called the cation exchange capacity (CEC). Soils with high CEC not only hold more nutrients, they are better able to buffer or avoid rapid changes in the soil solution levels of these nutrients. A soil test will tell you the CEC number of your soil. Soils high in clay, silt, or organic matter will have a CEC number of 10 or greater, and no remediation is needed. Sandy soils will have a CEC number between 1 and 5. Adding organic matter to these soils will help increase the CEC.
There is more life below the soil surface than there is above. Soil life consists of burrowing animals, such as moles and earthworms, insects, and other soil creatures that are difficult or impossible to see without a microscope, such as mites, springtails, nematodes, viruses, algae, bacteria, yeast, actinomycetes, fungi, and protozoa. There are about 50 billion microbes in 1 tablespoon of soil. In a typical soil, each gram (what a standard paperclip weighs) likely contains these organisms, listed from largest to smallest:
Soil-dwellers move through the soil, creating channels that improve aeration and drainage. Nematodes and protozoa swim in the film of water around soil particles and feed on bacteria. Mites eat fungi, and fungi decompose soil organic matter. The microorganisms&#; primary role is to break down organic matter to obtain energy. Microorganisms help release essential nutrients and carbon dioxide and perform key roles in nitrogen fixation, the nitrogen and phosphorus cycles, denitrification, immobilization, and mineralization. Microbes must have a constant supply of organic matter, or their numbers will decline. Conditions that favor soil life also promote plant growth.
Unfavorable soil conditions, such as high temperatures, compaction, or oversaturation can injure beneficial soil life. This can lead to a proliferation of disease-causing fungi, bacteria, or viruses. To read more about common soil diseases see chapter 5,&#;Diseases and Disorders.&#; Plants that are stressed by disease are often more susceptible to insect damage. More information on insects can be found in chapter 4, &#;Insects.&#; To learn more about managing insects and diseases, please see chapter 8, &#;IPM.&#;
To promote soil organisms, incorporate organic matter, till as little as possible, minimize soil compaction, maintain favorable soil pH and fertility, and use organic mulch on the soil surface.
1. Do I have to get a soil test report or can you just tell me how much fertilizer to add?
A soil test is the only accurate way to determine the amount of fertilizer needed for each individual yard. A soil test is a process by which nutrients are chemically removed from the soil and measured for their &#;plant available content&#; within the sample. The quantity of nutrients extracted is used to determine the type and amount of fertilizer to be recommended. The pH and acidity of the soil sample is also measured and used to determine if lime is needed and how much. Soil testing is provided by the NCDA&CS. There is a small fee for each soil sample submitted to the NCDA&CS during December through March, which is the peak season for soil testing in North Carolina. There is no fee for soil samples submitted to the NCDA&CS during the rest of the year (April through November). Samples must be mailed in to the NCDA&CS and boxes are available at their main office, Reedy Creek Road, Raleigh, NC, or at any county Cooperative Extension center. More information and forms are available on the NCDA&CS website.
2. How often should soil be tested?
If a soil test report indicates the pH and nutrient levels are in the range needed for plants to be grown, you may not need to sample every year. As a general rule, sandy-textured soils should be tested every two to three years and clay soils every three to four years. However, if nutrient or pH levels are excessively high or low, you should submit a sample every year to determine how much improvement has been achieved and what additional amendments should be made. In addition, if problems occur during the growing season, collect a sample and have it analyzed.
3. Can I add Epsom salts to my plants?
Epsom salt (magnesium sulfate) can sometimes be beneficial, especially in sandy soils that may be low in sulfur or magnesium. However, the best recourse is to rely upon a soil test and make adjustments to the soil pH and nutrient content based on the soil test report&#;s lime and fertilizer recommendations.
4. Why are my (azalea, blueberries, maple, rhododendron) leaves yellow?
Ruling out water issues, the likely culprit is pH. Azaleas, blueberries, maples, and rhododendrons are acid-loving plants requiring a pH of 4.5&#;6.0 to thrive. Knowing your soil pH will help you select plants that will thrive in your soil. Altering the pH of a soil is difficult, but can be done in small areas. Refer back to the section on soil pH for more information.
5. My shrubs/trees are wilting, the leaves are brown on the edges, and are falling off. What is causing this?
This could be the result of salt injury due to improper application of fertilizer. High salts decrease a plant's ability to extract water from the soil, and salts can move through the plant's vascular system to the leaves where the water evaporates and concentrates the salt to toxic levels. Plants may recover from salt/fertilizer injury if high levels of salts are reduced through repeated, deep irrigation. The best defense against this problem is to obtain a soil test and follow the fertilizer recommendations. Avoid the use of high salt fertilizers such as sodium nitrate; use slow release fertilizers and apply correctly. Azaleas and blueberries are very susceptible to salt/fertilizer injury.
6. My soil is very heavy clay. What can I do?
7. The soil in my lawn is compacted; what can I do to resolve this?
Foot traffic, mowing, recent home construction, and even rainfall can contribute to soil compaction, which can be especially problematic in clay soils. Turf grass roots need air and water to grow. Core aeration is the removal of small cores from the top few inches of soil to allow air, water, and nutrients to enter the root zone of your turf. The result is reduced water runoff and enhanced water and nutrient uptake, gas uptake, thatch breakdown, and heat and drought tolerance of your turf.
The best time to perform core aeration is when grass is actively growing. That means late spring or early summer for warm-season grasses and fall for cool-season grasses. The soil should be moist, but not wet. Be sure to mark sprinkler heads, shallow lines from the sprinkler, and underground utility, cable, and septic lines to prevent damage. Soil cores should be left on the lawn; they will work their way back into the soil within two to four weeks. Lawns may be fertilized, seeded, or top dressed with a soil amendment immediately after coring, although ensure the timing of fertilization corresponds with the recommendations on the maintenance calendar (content.ces.ncsu.edu/catalog/series/227) for your turf. Lawns can be aerated once a year, especially under heavy use conditions and with heavy clay soils. Note that spike aeration is not recommended, as this method of aeration only further compacts the soil.
Brady, Nyle C., and Ray R. Weil. The Nature and Properties of Soils. 14th ed. Upper Saddle River, New Jersey: Prentice Hall, Inc, . Print.
Buol, S. W., et al. Soil Genesis and Classification. 6th ed. Hoboken, New Jersey: John Wiley & Sons Inc., . Print.
The company is the world’s best Soil Remediation powder supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
Dunne, Niall, ed. Healthy Soils for Sustainable Gardens. Brooklyn, New York: Brooklyn Botanic Garden, . Print.
Maynard, Donald N., and George J. Hochmuth. Knott's Handbook for Vegetable Growers. 5th ed. Hoboken, New Jersey: John Wiley & Sons, Inc., . Print.
Soil Fertility Manual. 5th ed. Peachtree Corners, Georgia: International Plant Nutrition Institute, . Print.
Author:
Luke Gatiboni, Extension Soil Fertility Specialist and Assistant Professor, Department of Crop and Soil Sciences
Contributions by Extension Agents:
Jeana Myers
Contributions by Extension Master Gardener Volunteers:
Deborah Green, Kim Curlee, Judy Bates, Jackie Weedon, Karen Damari, Connie Schultz, Edna Burger
Content Editors:
Lucy Bradley, Associate Professor and Extension Specialist, Urban Horticulture, NC State University; Director, NC State Extension Master Gardener program
Kathleen Moore, Urban Horticulturist
Copy Editor:
Barbara Scott
How to Cite This Chapter:
Gatiboni, L. . Soils and Plant Nutrients, Chapter 1. In: K.A. Moore, and. L.K. Bradley (eds). North Carolina Extension Gardener Handbook, 2nd ed. NC State Extension, Raleigh, NC. <https://content.ces.ncsu.edu/extension-gardener-handbook/1-soils-and-plant-nutrients>
Luke Gatiboni
Find more information at the following NC State Extension websites:
Extension Gardener Gardening Horticulture Soil FertilityN.C. Cooperative Extension prohibits discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status.
This publication printed on: Sept. 22,
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Soil contamination, caused by human activity, harms the environment and threatens human health. Soil remediation targets these harmful contaminants to create safer, cleaner soil. Thanks to improvements in soil cleanup technology, inhospitable land areas are becoming once again useful for human and animal life. It&#;s essential to understand how soil remediation works and how it can improve the environment.
Learn how your business can be more environmentally friendly through soil remediation.
Soil remediation is a specific type of environmental remediation, which deals with cleaning up hazardous materials from the environment. It&#;s the process of removing contaminants from the soil, restoring it to a clean and safe condition. Contaminants can include a wide range of harmful chemicals and materials, each of which threatens both the environment and human safety. Several different strategies are available for soil remediation. Depending on variable factors, the process can be either short-term or long-term.
Large toxic waste dump sites sparked public outcry in the s when people learned of human health and safety dangers. In response, Congress created the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), known as Superfund. The act grants power to the Environmental Protection Agency (EPA) to:
Soil remediation is vital for many reasons. The contaminants found in soil are dangerous and harmful for plants, animals and humans. In addition, pollution renders land areas useless &#; soil remediation makes space usable again.
When pollution affects the soil, it is detrimental to plant and animal life. Plants feel the impact first. They rely on soil nutrients to survive, and their roots take up contaminants. Depending on the contaminants and how prevalent they are, they can be fatal for plant life. Contaminated soil also affects animals, since touching or interacting with polluted soil and eating contaminated plants can cause health issues. Soil contamination can destroy entire ecosystems because it often results in the loss of habitat for wildlife.
Soil contamination is also a public health concern. Eating a contaminated plant or animal can cause serious harm, as can touching the soil itself. Because animals could consume contaminated plants and wander on, it becomes difficult to know what animals are safe to eat. Those who work or live in proximity to contaminated soil face serious health risks.
Contamination can render large plots of land inhospitable and unusable. Soil remediation frees up land for investment, development or restoring natural habitats, which is another reason it&#;s so important.
Soil contamination is a broad term and can include various chemicals and materials from different sources. Some common sources of soil contamination include:
From these sources arise specific soil pollutants. Each pollutant category poses a unique risk to the environment and human health. Cleaning efforts and strategies depend on the nature of the pollutants.
Polychlorinated biphenyls (PCBs) are manufactured chemicals including carbon, hydrogen and chlorine, also known as chlorinated hydrocarbons. PCBs&#; properties, such as structure and consistency, vary depending on the amount and arrangement of chlorine atoms. Consistency varies from liquid to waxy, and color varies from light to black.
Until the Toxic Substances Control Act banned PCB manufacturing in , they were produced for many applications, from heat transfer to pigmentation. Because they can last a long time without breaking down, they continue to affect the environment. PCBs can potentially cause cancer and damage the immune, reproductive, endocrine and nervous systems of exposed humans and animals. Soil remediation can help remove PCBs from the environment.
Volatile organic compounds (VOCs) are also human-made. They&#;re produced during the manufacturing of many products, such as paints and refrigerants. They emit over time as gases from manufactured products, causing adverse health effects. They permeate natural environments &#; VOCs are common contaminants in soils.
Radioactive atoms have unstable nuclei, which causes them to emit electromagnetic waves or streams of subatomic particles. Radioactive contamination reach soils in multiple ways, including:
While some radioactive materials occur naturally, an overabundance can degrade soil, making it unable to host plants. Radioactive contamination in soil renders areas unsafe, as these materials pose serious human health risks, depending on the length and severity of the exposure. High doses of radiation can cause Acute Radiation Syndrome, Cutaneous Radiation Injury and an increased risk of developing cancer long-term. Soil remediation can target these dangerous materials.
Heavy metals contamination is a major source of soil pollution, deriving from leaded gasoline, paint, fertilizer, sewage and many other sources. Some common metal contaminants include:
These metals sink into soils and often resist breaking down for a long time. They can cause human health risks by contaminating plants and water sources. Hazardous metals are another targeted soil pollutant through remediation efforts.
Human activities such as agriculture have led to unnaturally high quantities of organic compounds in soil. Examples of organic compounds include:
These organic compounds dilute throughout the world&#;s soil. They can be challenging to identify, measure and track, but remediation can help reduce their quantity.
Another type of soil pollution includes pathogens. Pathogens can kill plant life, affecting ecosystems. Human activities contribute to a higher density of soil-borne pathogens. Livestock waste contains bacteria and viruses, and wastewater used for irrigation can expose soil to further pathogens. When pathogens spread through agricultural practices, food can become contaminated. Pathogens are another contaminant that remediation targets.
Contaminated soil remediation is a complex, advanced process. It takes time to clean and repair affected soil. How long the process takes depends on certain variables.
Soil remediation projects can be short- or long-term, with short-term projects requiring less than a year. Short-term remediation involves separating contaminated and clean soils. A liner directs runoff liquid away from the clean soil area. With the liner removed, clean soil remains. Long-term projects are more intensive and last longer than a year. These projects necessitate long-lasting liquid containment solutions.
Several soil remediation methods are available, utilizing physical, chemical and biological techniques. The process can be either &#;in-situ&#; or &#;ex-situ.&#; In-situ means the process happens on-site, while ex-situ soil remediation involves excavation and off-site treatment within soil remediation plants. Here are some of the strategies used to clean contaminated soil.
As an ex-situ treatment method, excavation and removal are one form of soil remediation. The first step is the removal of possible contamination sources, like chemical-filled drums and debris. Then, experts test the soil to identify what contaminants are present. They excavate any polluted soil using construction equipment, like backhoes, and pump away present water.
Professionals cover the excavated soil with tarps to ensure wind and rain don&#;t blow or wash it away. It&#;s either taken to a landfill or left covered on-site. The process is complete when test results reveal safe soil in the surrounding area.
Capping is another way to protect environments from soil contaminants. Capping involves placing a cover over contaminated materials &#; it does not destroy or remove the contaminants, but it does prevent them from spreading further. Capping stops moving water from carrying contaminants to water sources, and it prevents wind from blowing the pollutants off-site. It also stops leaking gas from volatile organic compounds.
Several different types of caps are available, and many experts choose to combine them. Concrete or asphalt slabs can double as parking lots or building foundations, while other coverings include clean soil and vegetation, with a drainage pipe between. A geomembrane helps prevent gas leakage and water drainage.
Another method is solidification, which binds the waste in a solid block. While this technique does not destroy the pollutants, it prevents them from leaking into the surrounding environment by trapping them in place. Common binding agents include:
Some binding agents also produce a chemical stabilizing reaction. For example, a water and limestone powder mixture will affect any metal pollutants in the soil, rendering them unable to dissolve in water. Solidification and stabilization are possible either in-situ or ex-situ. On-site, augers drill holes into the ground for injecting and mixing the additives. Off-site, pug mills grind and mix excavated soil.
In-situ thermal treatments use heat to move the contaminants within the soil. It&#;s one of the more advanced soil remediation technologies. In essence, the extreme heat levels vaporize the chemicals. Once gaseous, the chemicals travel through the soil and become easier to remove, allowing for soil vapor extraction. Three different methods are available to generate the heat:
As the name suggests, bioremediation uses microscopic life to eat away contaminants. Microbes will feed on petroleum products, certain solvents and pesticides. Then, they will digest the contaminants and produce trace amounts of carbon dioxide, water or ethane. Bioremediation depends on favorable conditions for these microbes. To support microbial life, one can add oxygen-producing chemicals or vegetable oil to the soil using a well. Bioremediation is a favorable option since it eliminates pollutants. However, it can take months or years.
Pollution affects the entire natural environment, not just the soil &#; contaminants that start in the soil often wind up in freshwater sources. Remediation is also necessary for sediment, surface water and groundwater.
The EPA&#;s Superfund also targets contaminated sediment. Methods for cleaning up pollutants in sediment are similar to those for cleaning up soil. The EPA uses natural processes, capping, dredging or excavation techniques.
It&#;s imperative to keep surface waters clean, as human contact with surface water is likely. Thankfully, surface water is also easy to access. One technique for surface water remediation is air stripping, which involves transferring volatile organic compounds within liquid into an airstream.
Several methods are useful for groundwater remediation, as well. One strategy has earned the appropriate name &#;pump and treat,&#; which describes the process. Wells bring groundwater into above-ground treatment systems. Another technique is to use a permeable reactive barrier. These barriers are permeable because they allow some substances to escape while retaining contaminants.
Soil remediation techniques make the environment cleaner and safer for plant, animal and human life. They remove or contain harmful contaminants such as PCBs, volatile chemicals, radioactive materials, metals, organic compounds and pathogens. Several different processes for soil remediation are available, with some being more effective than others and some being quicker than others.
If you&#;re wondering how or when to do soil remediation, consider contacting the VLS Environmental Solutions (VLS). At VLS, we process and transport residual waste, ensuring compliance with all regulations. We offer comprehensive soil remediation services and we can help you pursue environmental sustainability through soil remediation. Contact us at VLS to learn more.
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