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The Ultimate Guide to Soil Horizons

Have you ever thought about the ground that’s beneath your feet and what is it composed of? We might think it’s just plain dirt, but scientists have determined that six different soil horizons make up the different soil profiles of the ground. Learn more about these soil horizons and what impact they can have on your gardening efforts.

What is a Soil Horizon?

Simply put, a soil horizon is a distinct layer in the ground. These six layers are made up of different substances that either look different, have different chemical makeups, or are physically different from the other layers. 

Soil horizons act as the history of the soil in a particular area. The layers are formed in a specific way due to the original composition of the land, the weather, the vegetation of the area, and other factors. Think of this as the biography of the soil.  

What are the Six Soil Horizons?

The six soil horizons are labeled with a letter denotation and are O, A, E, B, C, and R. Each of these soil horizon layers are unique. O is the soil horizon that is made up of organic materials. Soil horizon A is the layer that is made up of minerals. E is the soil horizon that’s comprised of eluviated soil, or soil layers that have gained materials from other layers by water movement. Soil horizon B is made up of subsoil. C is the soil horizon that contains parent material. Finally, R is the soil horizon that’s bedrock.

Soil Horizon O

Soil horizon O is made up of the organic matter or humus that falls on the soil. This organic matter has decomposed down and created a layer of soil. The O soil horizon can vary when it comes to the size of the segment.

Soil Horizon A

When you think of dirt, you probably imagine soil horizon A. It is the topsoil. It has a combination of organic matter and minerals located in it. Soil horizon A is the best for growing plants. It is always at the surface of the soil, as that is where it forms; however, it can show up again deeper in the layers. If there is a natural event, such as flooding or a landslide, that moves the ground, this layer can go deeper into the soil profile. This layer is often dark in color. 

Soil Horizon E

Soil horizon E is a complex layer that is mostly sand, quartz silt particles, and other material that can’t be leached away. It is formed by the organic materials, clay, and any minerals being leached out of the soil. Anything that can’t be leached out of the soil is left behind and makes up this layer. Soil horizon E is often found in forests and areas with old soil that hasn’t been disturbed in a long time. This layer is often lighter in color than other layers because much of it has leached into lower layers.

Soil Horizon B

Soil horizon B is the subsoil layer. All of the materials, such as minerals that are leached from the soil horizon A and E, make up this layer in the soil profile. Often, it has iron, soluble salts, and clay accumulated in it. Erosion can sometimes expose this layer to the surface, in addition to some manmade causes. Bulldozers and landscaping can also result in erosion that exposes it.

Soil Horizon C

Soil Horizon C is the parent material layer. The Earth’s surface deposits created this layer. It could have been produced by glaciers moving across the earth, lake sediment, or the exposure of bedrock. 

Soil Horizon R

Soil horizon R is made up of bedrock. The rocks typically found in this layer include limestone, quartzite, sandstone, basalt, and granite. In areas where the bedrock is exposed at the surface of the ground, these materials will weather. The materials that weather off of the bedrock become the soil horizon C. This horizon is technically not soil and is usually found under soil horizon C. 

Does All Soil Have All Six Soil Horizons?

There is no specific reason for soil horizons. Some soil profiles will have every single one of the six soil horizons in it. Other areas will have fewer soil horizons in their soil compositions. An example would be some may have just O, or O, E, and B, or A and C. In some spots, there may be soil horizons that repeat in different layers. An example here would be A, B, E, and B. Keep in mind that the majority of soil profiles will have A, B, and C horizons in them. Also, some may also include an O horizon in addition to these three major soil horizons. 

Not only can soil profiles have all six soil horizons, fewer than six soil horizons, or have repeating profiles, they can be found in any order. Soil horizons don’t have a set order for how the horizons appear in the soil profile. It all depends on how the soil was formed over time and the surrounding conditions.

Gardeners and Soil Horizons

Gardeners may not think too much about the soil horizons in their garden plots or the history of their soil, but it can help them to make informed decisions. Examining the soil horizons in the area you plan on planting can give you an idea of whether or not you may need to add some soil amendments to make the soil more fertile or to add loosen up soil that has a high clay content. Knowing your soil horizons can help you to determine what’s necessary to get your garden growing healthy and strong.

The soil horizons that make up your backyard may be exactly what you need to have a bountiful garden that doesn’t need much help. That scenario isn’t always what happens, so learning about soil horizons can be applied to your gardening efforts. Your garden soil will thank you with beautiful blooms and a nice harvest.    

How Does Soil Erosion Affect Soil Fertility

The usual image that comes to mind when thinking about erosion is beach erosion and other areas where the land has very noticeable changes due to erosion. It’s often straightforward to see the impact that erosion has on these areas because there are visible changes to the landscape. Soil erosion can result in changes that aren’t visible that can have just as devastating an impact as a beach disappearing over time. 

As a gardener, you may find yourself in a situation where you have to deal with soil erosion, as it can harm the fertility of the soil in your garden.

What is Soil Fertility?

Soil fertility is the concept of how well the soil can provide a habitat for life. Rich, fertile soil is the home of diverse organisms and is able to grow a variety of plants that result in a plentiful harvest of top-quality fruits and vegetables. A backyard garden that has fertile soil doesn’t need any amendments to it to ensure that your crop does well. A garden that has soil fertility issues will struggle to yield a quality harvest.

What Factors Contribute to Soil Fertility?

Several factors contribute to soil fertility. The soil needs to be deep enough for roots to grow and water to be retained in it. Weak root growth or water that evaporates too quickly will result in plants that don’t thrive. There also needs to be some drainage in the soil. More clay-based soils can result in poor drainage. This drainage issue can result in plants having their roots rot, and often ends in the plant dying. Also, drainage issues often mean that the soil is too hard without aeration for the roots.

The amount of organic matter that is found in the soil is also essential. Organic matter helps with soil structure and moisture, along with putting minerals and nutrients into the soil. A lack of organic matter will often result in plants that are probably not getting the right mix of nutrients to grow. Fertile soil also has the perfect pH. It should range from 5.5 to 7.0 for most plants. There are some plants, such as blueberries, that prefer soil outside of this pH range, but for most plants, this range is the sweet spot.

Another aspect of soil fertility is the other organisms in the soil. Some gardeners think of every organism that invades their garden as a pest or a problem that needs to be eradicated, but that’s not always the case. There are beneficial microorganisms that live in the soil that help plants grow, such as mycorrhizae. Poor soil quality often results in the death or migration of these microorganisms. 

Why is Soil Fertility Important?

Often, when there are issues with the growth of a plant or the harvest, there are two potential causes. One is pests, while the other is soil fertility. Soil fertility is vital for the soil to provide the perfect medium for any plants to grow. Problems with the fertility of the soil will show up during the growing season. Gardeners may find that their seedlings don’t grow as they should or that the leaves of the plants are yellowing when they should be a healthy green. The fertility of the soil must be addressed to help treat any issues and prevent them from occurring again in the future.

How Does Erosion Affect Soil Fertility?

Soil erosion can have an impact on soil fertility. The soil in your garden is in layers that have been deposited over time. Often, the top layer that you plant your garden in is called topsoil. Erosion erases away the top layers of the topsoil over time. As topsoil is often one of the most fertile areas, you’re losing some of the qualities that make your soil fertile. Loss of soil fertility can be a huge problem for gardeners that can’t be ignored.

Testing Your Soil

One of the first things that should be done if you think there’s a problem with the fertility of your soil is to test it. Testing is a valuable tool that can help you address any lack of nutrients or minerals in the soil that’s impacting your crops or flowers. There are two options when it comes to testing. 

You can pick up a DIY kit that allows you to take several samples from around your garden and test the soil yourself. These kits can require that you follow the directions exactly to get the correct results, so it is imperative to read the instructions carefully a few times before you get started. 

The other option is to send your soil samples off to a lab to have them tested for you. For this option, you’ll need to collect the soil using the directions they send. Usually, these directions are that you have to collect at an appropriate depth and in several areas to get an overall feel for your soil’s health.

Once you receive the test results, you can use them to amend the soil as needed. You may find that you need a general application of fertilizer to boost the nutrients in the soil or that you need only one particular nutrient. Problems with pH can also be found at this time. 

Soil Fertility Assistance

After you’ve tested the soil, you should also look into the physical nature of the soil. How deep does your garden bed go down? Does your soil contain clay? When it rains, does your garden become a muddy mess? Any of these issues should be adjusted. For instance, you can add lighter amendments to the soil that’s high in clay.

Soil erosion can cause issues with your garden and how well it will grow over the season. Adding minerals and nutrients to it may be necessary if the erosion has taken away too much of what makes your soil fertile. Testing your soil is one of the best methods of ensuring that your soil remains viable for this growing season and beyond. 

Economic Effects of Soil Erosion

In today’s changing climate, the effects of soil erosion are prevalent. While forest land, or land that is surrounded by or covered with vegetation, usually sees little effects of soil erosion, cultivated land certainly does. The practice of clearing land for agriculture serves to increase its vulnerability as unprotected land is susceptible to frequent and sustained soil erosion.

Erosion occurs when the land’s soil is not adequately covered in order to protect it from wind, water, and sand. This erosion causes the soil’s health to decline as well as affects surrounding resources such as air and water quality. Heavy flooding or storms can exacerbate the problem or be the cause of erosion in the first place. Overall, erosion can reduce the land’s ability to produce harvests and lead to economic hardship.

Economic Effects of Soil Erosion

In the United States alone, soil erosion accounts for $12 billion in losses. In comparison, Asia and Europe tally $3.5 and $4.5 billion respectively. Several industries are affected by the loss of soil quality or the degradation of crops and their yields. 

  • Meat and Dairy: Chicken, cattle, and swine are all affected by soil erosion. As the quality of their feed depletes, the quality of meat declines. Animals may be drinking water contaminated by runoff or their feed might not contain enough nutrients.
  • Fruits and Vegetables: When crops don’t produce their expected yield, prices go up. Supply and demand still rule the day and if production is reduced or quality degraded, prices may spike for produce that is usable.
  • Grains: Since grains are converted into feed for livestock and processed into bread and flour, the degradation of their quality has a trickle-down effect and finds its way into the bread on the dinner table.

Effects of Soil Erosion on the Environment

Rattan Lal, from the School of Natural Resources at The Ohio State University, describes the condition as such: “Soil erosion exacerbates soil degradation and vice versa. In some cases decline in soil quality, especially the weakening of structural units, precedes erosion. In others, erosion may lead to a decline in soil quality and set in motion the degradative trend. In fact, soil erosion can be a manifestation of soil degradation because it involves physical removal of soil in a vertical and/or horizontal direction and degrades soil quality. It is a natural process that has shaped the landscape and led to formations of fertile alluvial and loess soils. However, the acceleration of the process through anthropogenic perturbations can have severe impacts on soil and environmental quality.”

Those impacts include damage to lakes and streams from runoff. As disturbed soil is washed away and deposited elsewhere, natural water resources are inevitably impacted. This erosion wreaks havoc on the land by removing the topsoil and over time, reducing its depth. This depth reduction causes roots to struggle to take hold. Topsoil degradation means soil loses its ability to trap and filter water, diminishing its benefits.

The soil’s fertility is called into question as well as nutrients are washed away. Young plants might not stand a chance from the onslaught of wind and rain and may be lost altogether.

Sediment is a serious impact of soil erosion as the runoff has to go somewhere and turn into something. Nearby roads and neighboring properties might find sediment deposits. Long-term excessive erosion can lead to weakened bridges and other infrastructure. Sediment deposits might also accumulate downstream and cause flood hazards while disrupting fish spawning grounds. Sediment might carry pesticides and fertilizers in its make-up, leaving poisons in its devastating wake.

The economic impacts on environmental shifts caused by erosion are vast in possibility and depend on the affected area’s economic and industrial output.

Effects of Soil Erosion on Agriculture

Although it is difficult to assess agricultural losses because of the unpredictability of climate change and accompanying weather patterns, estimates of economic loss are heavy and impactful. Since tilled soil is more vulnerable than untilled soil, it usually suffers the worst effects of erosion and influences agriculture by lessening the land’s ability to produce crops.

Erosion carries away not just soil but also the nutrients it contains. Studies show that each ton of soil that erodes might contain the equivalent of 2.32 pounds of nitrogen and one pound of phosphorous. When these elements are carried away, they are deposited in places adversely affected by excess nitrogen and phosphorous, not to mention pesticides. Per-acre dollar estimates work out to fertilizer losses at a cost of $2.10 per ton of soil loss.

The impact on agriculture in terms of time is also weighty. Farmers spend crucial growing time preventing erosion or repairing its damage. Eroded areas must be leveled with additional cultivation as well as filling gullies created by runoff. Gradually, topsoil suffers and depth is lost. Seeds and seedlings might also be washed away, adding to crop and economic losses.

Conservation Practices and Erosion Control

There are methods to minimize the damage of soil erosion and possibly prevent it from occurring in the first place. The time to put these into practice is before the next rainy season or the next predicted storm.

  • Crop rotation: Alternating crops on the same land can maintain soil productivity.
  • Contour farming: Sloped land can be tilled to make elevations more consistent and furrows can be created to serve as reservoirs. Terraced planting has a similar effect as crops are planted in graduated platforms to deter erosion.
  • Strip cropping: Alternating crops to be cultivated with strips of sod-forming or matting textiles like coir blankets and logs can also work to minimize erosion.
  • Subsoiling: This method works by circulating the soil to increase root aeration and give water a place to go, providing better access to crops that need it for survival. 

Lal goes on to say that, “Estimates of the global extent of soil erosion are tentative and subjective, and need to be improved by using remote sensing, GIS and other modern techniques. Developing a credible database is crucial to identifying management strategies. Erosional hot spots of the world … are in need of coordinated efforts at the global scale to restore degraded ecosystems.’

Soil erosion and shifting climates both affect the viability of soil used in necessary, everday industries. With conservation methods and soil stabilization products, erosion can be reduced and prevented, salvaging one of the most important resources.

Soil texture

Dig your hands down into the earth. What do you feel? Every handful of soil has its own individual texture, and those characteristics offer a significant contribution to crops. What determines the unique textures of soil? Why is it important, and which type of soil has more erosion resistance? Find the answers to these questions and more with this informative article.

What Is Soil Texture?

When a pedologist mentions ‘soil texture,’ they’re referring to the amount of various sized sand, clay, and silt particles in a sample of dirt. The composition of these grains makes up the inorganic parts of soil and are the bits and pieces that bind with organic matter to form topsoil.

The size of soil’s particles and their spacing also determines how much water will flow through it. Soil with a higher concentration of large grains of sand will have a greater infiltration rate, while dirt that is primarily clay will pool water on its surface as opposed to absorbing it.

Soil Textural Classes

A soil’s textural classification refers to the combination of sand, silt, and clay that make up the soil. It can be determined using exploratory research methods such as feel. A coarse-textured soil is probably composed primarily of sand, while a fine-textured soil is most commonly dominated by clay.

Farmers can also take a quantitative approach with a hydrometer. With this lab-based method, the soil is mixed with a sodium hexametaphosphate solution to separate the earth’s aggregates into identifiable parts. The U.S. Department of Agriculture outlines 12 primary soil texture classifications including the four most common types: sand, loam, silt, and clay.

Sand

Sand is the largest sized dirt particle. Each grain ranges in size from 2.0 mm down to 0.05 mm. It feels gritty to the touch. Since sand is just a bit of gravel, it drains well but doesn’t do an adequate job of retaining essential water and nutrients. Gravel particles that are larger than 2.0 mm are not considered when determining texture.

Loam

The soil that’s referred to as loam offers a proportion of 40% sand, 40% silt, and 20% clay in a single sample. It’s often the dirt of choice for making bricks and provides plenty of organic material for growing crops.

Silt

Silt particles are considered moderate in size. However, with sizes ranging from 0.05 mm down to 0.002 mm, individual particles are too small to see with the naked eye. It has a similar shape as sand particles, just worn down to a smooth texture.

While it’s not as strong as sand, silt is better at holding both water and nutrients. Because it’s prone to losing small amounts of minerals from each particle, silty soil generally makes more minerals available to your plants.

Clay

The smallest sized dirt particle, clay is less than 0.002 mm in diameter. To put that in perspective, you’ll need to line up 12,000 clay particles side by side to measure one inch. Clay feels sticky in your hands and is an excellent building medium.

What Determines the Texture of the Soil?

The percentage of materials determines a soil’s textural class, including the common particles we’ve already met: sand, silt, loam, and clay. Its texture is an important characteristic that influences a diverse number of properties, including water infiltration rates, aeration, susceptibility to erosion, and pH buffering capacity.

The Importance of Soil Texture

The texture of your field’s soil is essential to a successful harvest on a variety of levels. From saturation to water-holding capacity, let’s discuss each component of soil texture’s importance.

Infiltration

The amount of clay, sand, or silt in the dirt defines the rate at which water is able to drain through it. Once saturated, water moves more quickly through sandy soils than it does through soil that’s heavy in clay.

Availability

Soil texture influences how much water is available to your plants. Once your field’s saturation level reaches capacity, your clay soil will hold more water than its sandy counterpart.

Drainage

Well-drained fields are usually a sign of proper soil aeration. This texture of dirt is rich with air, which promotes a healthy root system and leads to a bumper crop.

Erosion

Different textured soils also respond differently to erosion. Some are more susceptible to loss based on their percentage of silt and clay particles. Those soils have a higher erodibility level than a sandy soil under the same weather and tilling conditions.

Organic Matter

Various soil textures also offer different levels of organic matter. This material breaks down faster in sandy soils than in silt and clay, likely due to the higher availability of oxygen for decomposition.

How Soil Texture Affects Erosion

Now we understand that a soil’s texture is directly related to the amount of clay, silt, and sand particles it contains. But what does this have to do with soil erosion? Soil texture has two main effects on erosion.

First, it influences the rate of infiltration and water’s ability to enter the soil. When it rains, does the water run off rapidly? If so, then you probably have sandy soil. This type of dirt has large pores that act like pipes, channeling water right into the ground.

Does the water collect on the surface or in low lying areas? If it does, then you probably have clay soils that are not known for providing good drainage.

Second, some types of dirt particles don’t detach as easily as others. Silt particles wash away easily because they’re tiny and don’t readily combine with other soil aggregates.

Which Type of Soil Is More Erosion Resistant?

One study suggests that an estimated 30 tons of agricultural soil are lost in the United States to erosion each year. This loss outpaces the rate of formation by an astonishing eight times.

So, which type of soil offers the most erosion resistance? The answer is clay. Clay is better at resisting erosion because it’s small particles hold water, making it a stickier compound than sand.

A soil’s texture affects many aspects of your garden, including erosion. Use this handy guide to help determine your dirt’s composition and how you can use that information to help you conserve topsoil.

Soil analysis

If you’re a farmer with the goals of maximizing your crop production while protecting the environment from runoff, then analyze your soil. This simple test will protect your fields and adjacent waterways and save money. Before you drop a single seed this year, have a soil analysis done. You’ll conserve energy with a plan for fertilizing your fields, particularly if you’re a grower who mixes their own media.

Why Is Soil Testing Important?

There are several reasons why you want to test your field’s soil. Scientists conduct these tests for engineering, geochemical, and ecological investigations in addition to agricultural studies. This set of chemical processes determines the available nutrients in the ground and the various properties that are essential for prime soil health. Here are three top reasons to test your soil:

Crop Nutrition

One of the most commonly used tests in today’s agricultural industry is to determine the available combination of nutrients, composition, and the soil’s pH level. When armed with a recent soil analysis, farmers can accurately calculate the amount and type of fertilizer needed for maximum production.

A soil test will ascertain a field’s fertility, potential toxicities, and expected growth potential of the land as modeled by the Law of the Maximum. According to this universal law, it only takes one deficient nutrient to reduce a crop’s potential yield significantly.

Changes Over Time

A soil’s chemistry changes over time as natural and chemical processes break down its compounds. This theory is especially true for transplanted land that finds itself in a foreign ecosystem, with new flora and climate conditions. An accurate soil analysis will give you the tools to significantly improve the ground, particularly when analyzed within 24 hours after its extraction.

Soil Contaminants

Soil is often contaminated by a variety of elements such as arsenic, barium, cadmium, copper, mercury, zinc, and lead. Lead is particularly dangerous, and you can take several steps in your garden to reduce the risk of this unwanted mineral in your food. Place gardens far from heavily traveled roads and consider liming the ground as recommended by a soil test. A pH level of 6.5 minimizes lead availability.

What Are the Goals of Soil Analysis?

The overall goals of soil analysis are varied, from determining the level of available plant nutrients to predicting an increase in yields and profitability. Farmers can also use this test to calculate the necessary amount of fertilizer needed for each individual crop.

Laboratory Soil Tests

One option for land analysis is to hire a commercial lab. Choose a local facility when possible, as they are likely most familiar with the local soil’s chemistry. The advantage of this knowledge is the technicians know exactly which tests to perform that will reveal the most valuable information.

A laboratory soil analysis checks for all 13 mineral plant nutrients in three categories:

  • Major nutrients including potassium, nitrogen, and phosphorus.
  • Secondary nutrients including magnesium, sulfur, and calcium.
  • Minor nutrients that include manganese, zinc, boron, copper, molybdenum, chlorine, and iron.

In addition, your lab results will consist of a professional’s interpretation of the findings, along with expert recommendations. Your lab report will outline any anomalies, exceptions, and shortcomings in the soil samples.

Soil Sample Analysis

The technicians at Colorado State University recommend that farmers collect between 10 and 20 test samples for every 40 acres of land. By testing this wide assortment of specimens, you’ll have a good understanding of precisely what your soil needs in order to perform its best.

When you know your land’s nutrient content by the process of chemical analysis, it’s easy to determine the precise amount of additives needed to achieve the highest quality yields. Plants can tolerate soil with up to 80 percent nitrogen, 40 percent phosphorus, 60 percent potassium, and 40 percent magnesium.

When Should Soil Be Tested

Take your first soil samples annually in the fall, after you harvest and before adding any fertilizer. It’s best to collect your test subjects when the soil is at its optimum moisture level. In the case of permanent crops such as orchards and vineyards, conduct a soil sample analysis every four or five years.

How to Collect Soil Samples

Take your soil testing samples either by probe or with an old-fashioned shovel. If you decide to use a shovel, dig a pit, and cut the edges vertically along the wall, being careful not to let any dirt fall into the hole. Crop and remove the exposed dirt to the left and right of the soil you intend to collect for your samples.

If you plan to use a probe, take your sample at a depth of normal tillage. For field crops, that’s up to 30 cm or for permanent crops, take your sample between 30 to 60 cm. Collect enough dirt to complete a series of tests, with one kilogram of each soil sample being plenty to analyze. Then, separate each bit of dirt in a plastic bag and label it with the following information:

  1. The farmer or land owner’s name.
  2. Address.
  3. Designation of the plot.
  4. Depth of sampling.
  5. Any previous fertilization.
  6. Type of crop you plan to sow.
  7. Date of sample.

DIY Soil Test Kit

Do-it-yourself soil test kits are helpful. However, they usually only test for the three major nutrients as well as acidity. These electric meters are available at most gardening stores and measure pH, water content, and basic health of the soil.

It’s a well-known fact that laboratory tests are more accurate than the do-it-yourself kind. To make things easier, some labs offer a prepaid mail-in kit for field management and water testing. This process helps facilitate the packaging and delivery of samples for more extensive testing than the over-the-counter options, such as precise flow injection technology or near-infrared scanning.

Soil sample analysis is an essential part of the pre-growing season. The results are an indispensable tool for managing crop nutrition, and to wield this tool effectively, you must know how and when to take testing samples. Equipped with this helpful article, you’re well on your way to a healthy harvest this season.