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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 Moisture and Soil Erosion: What You Need to Know

Soil is formed partly from the effects of wind and rain. Throughout soil’s lifetime, it continues to be affected by the same elements. The effects of moisture on soil are determined by the moisture content for a given region and by taking into account the topography of the land. Current climate conditions have a significant impact on soil as land and sea temperatures continue to rise.

Erosion is a natural occurrence, yet when human-related activities (agriculture and development) change the structure of the land and therefore the soil, consequences take place. Determining whether an area is experiencing a drought or will experience one is measured by the soil’s moisture content. If the moisture content is too high, the risk of soil compaction rises. Soil that is dry or in arid climates may experience drought although that may change as climate does.

What Is Soil Moisture?

The level of moisture in the soil is often determined by variables in climate systems. Surface temperatures affect moisture levels through precipitation and evaporation. Drought and floods have severe impacts on soil moisture content in addition to the effects of climate change. As these conditions affect moisture content, they also indicate vulnerability to runoff and erosion.

Jamali Baruti, in a recent study of soil moisture in relation to soil erosion, explains: “Available water capacity (AWC) is the amount of water that the soil can store. It is the amount of water that is available for use by plants and is normally expressed as volume fractions or percentage.’ People have an adverse effect on soil’s AWC. Activities such as compacting soil with heavy equipment will decrease the amount of water soil can hold. Lower AWC makes soil more prone to drought.

Climate Change and Soil Moisture

The moisture content of soil has increased over the last 30 years: a trend that has coincided with rising temperatures due to climate change. As temperatures rise and rainfall increases, there is less chance for evaporation or for the soil to dry enough to lessen its water content.

Changes to the climate drive the global hydrologic cycle and intensify it. This cycle starts with oceanic evaporation that is lifted and cooled, then condensed into water vapor to forms clouds. Moisture is carried until it is deposited back to earth in the form of precipitation. As this cycle is disrupted, it opens the door for increases in ET or evapotranspiration which is the process of moisture up — then down — in the hydrologic cycle.

What Is Soil Erosion?

Soil erosion takes place when one or more contributing factors are in place, water not being the least. Soil erosion from water can be devastating as it strips the top layer of soil while diminishing the integrity of underlying soils. Debris and sediment are carried away and can change the soil’s composition resulting in loss of fertility or new plantings.

Soil Moisture and Erosion Combined

A combination of soil moisture and soil erosion can work to create a superlative amount of damage to an area. Erosion accounts for economic, environmental, and human health risks.

”Soil erosion rates vary widely over the landscapes, over a field and even along a slope profile within the field. To understand soil erosion over a particular area it is necessary to assess erosion at different landscapes for which various techniques are available,” says Mr. Baruti. 

Understanding moisture content is imperative to know what the health of the soil is at any given time and if steps can be taken to avoid drought or erosion. Testing soil for its moisture content with various soil moisture testing devices or techniques is recommended to minimize the impacts of erosion and moisture imbalances.

How to Test Soil Moisture

Gravimetric

By far the oldest method to measure soil moisture, the gravimetric process is lengthy and time-consuming. Soil samples are collected and weighed, then dried in an oven and weighed again, and compared for differences to estimated water content. The gravimetric method may prove difficult to apply if samples need to be taken from greater depths. Disruptions in the soil might also account for soil compromise as numerous samples might need to be collected for analysis.

Hand auger

These devices come with shaft extensions and are commonly used for deeper samples. Augers can be applied to depths up to 55 feet. The auger is turned by its handle which pushes its cylinder into the soil. The auger is then raised, and the cylinder’s barrel is emptied by striking it to free the sample. The gravimetric method can then be applied to the deeper sample.

Tensiometer

This device determines how much force a growing plant needs to absorb moisture from the soil. A tensiometer consists of a ceramic cup (porous point) connected to a measuring device. The cup is filled with water, and the water in the cup finds its balance with the soil. As the soil dries, water flows out of the cup to indicate greater tension. As soil becomes wet and its tension reduces, water flows back into the cup. Changes in these tensions are indicated on the instrument’s measuring device. Temperature can affect tensiometers as the gradients between the device’s porous point and the soil might cause variations in its measurements.

Moisture sensors or probes

Soil moisture sensors test for moisture volume through electrical resistance, dielectric constant, or through interactions with soil neutrons. These instruments run the spectrum from a low-end do-it-yourself type up to more sophisticated devices that can also measure soil pH and determine soil temperature. Simply insert the probe into the soil, and the instrument does the rest.

Soil erosion is a serious consequence of agriculture and development. A warming planet is disrupting its cycles to create balance in soil’s moisture content. As these imbalances increase or fail to stabilize, drought, runoff, or erosion might result.

Testing soil for its moisture volume is one way to find out what’s coming. Take measures to increase soil’s ability to infiltrate or drain to avoid conditions that contribute to adverse consequences. Working to prevent problems now can positively affect two important factors — agriculture and development.

What Does Soil Need to Stay Healthy?

The key to any beautiful yard or garden is healthy soil. Essential for providing nutrients and support, healthy soil can make or break your landscaping or gardening efforts. For some homeowners, the soil around the house isn’t ideal for growing the plants they want, which can make it almost impossible to create the yard of their dreams. Indoor or patio container gardens can struggle with the same issue. 

Luckily, there are several ways you can improve the health of your soil, whether in your yard or in a container garden. We’ve created this guide to provide information about what makes healthy soil and ways you can improve it. 

What Makes Healthy Soil

Gardeners have many opinions on what makes soil healthy. Often, soil health depends on the region, its soil type, and the plant life it supports. Some attributes of soil that are important to be aware of include:

  • Texture: Soil comes in many types, typically categorized as sand, silt, or clay. Many regions have soil that is a mix of these three types. Sand is the loosest, while clay is the most tightly packed.
  • Organic Matter: Organic matter can affect your soil in a number of ways, ranging from soil adhesion to absorption to food for the organisms that live below ground.
  • Air Retention: Ideally, soil should have about 25% air retention. This gets oxygen to the roots without allowing so much air that the plant rots.
  • Water Retention: Soil should also have about 25% water retention to allow for the formation of both large and small soil particles. This helps support plant movement and the presence of soil life.
  • Soil Life: Everything from mites to earthworms make their home in the soil, and their presence provides plants with much-needed nutrients. In addition, their movement in the ground keeps soil from getting too packed. 
  • pH Balance: pH level is one of the trickiest components to balance but is very important to your soil’s health. Some plants need more basic soil while others thrive on acidity. Being aware of and manipulating your soil’s pH balance can make a huge impact on the success of any garden or landscaping.

These factors all contribute to healthy soil. Knowing how to improve them can help plant life thrive. To tell what type of soil you have and whether you need to make any changes, fill one-third of a jar with water. Add soil, and shake the jar until everything is mixed. Leave it overnight; it should stratify into different levels as it settles, with the organic matter on top. Mark the different levels so you know your ratio of soil types. Make sure there’s organic matter on top. If not, you need to add some into your soil. 

Improving Potting Mix

Potting mix is a difficult substrate to get right. Container gardens are less flexible than yard gardens because they’re self-contained. One of the best ways to improve a potting mix is to add another substrate to enhance both the texture and the nutrients. Coir is a great organic soil additive to help your potted plants thrive. Thanks to its porous nature, coir keeps oxygen in the soil while still providing the needed nutrients. Because it’s so absorbent, it is also easy to re-wet. This helps your plants stay healthy if you’re dealing with dry conditions. 

To use coir as a potting mix, start with your favorite potting soil. Place a coir brick in a large container with plenty of water. It’s important to use a container that’s big enough: Coir expands significantly when soaking. After you’ve soaked the substrate fully, mix it in with your soil. We recommend a 40% coir to 60% soil mixture. It’s important to note that because coir is so absorbent, you have to be very careful about salt buildup. 

Another popular alternative is homemade compost. Start with a compost bin in your kitchen or outside and only add items that will compost properly. A good rule of thumb is to think of things that rot easily. Common composting items include eggshells, fruit and vegetable scraps, grass and plant clippings, coffee grounds, and shredded newspaper. 

Once these items begin to rot and mix together, simply combine them with a little soil and use the resulting compost as a nutrient-rich additive for your container garden. Add a few inches to the garden once a year, as the nutrients will seep into the soil over time.

Soil Amendment

You can improve the soil in your yard, as well. Start by determining your main soil makeup, based on the trick mentioned previously. Depending on what you find, you can figure out what additives to use to improve the overall health. It’s important to consider what sort of plants you want before you dive into soil amendment. For example, coir has a more balanced pH balance, making it good for plants such as ferns and asparagus. Peat moss is more acidic, which is perfect for acid-loving plants such as azaleas, blueberries, and camellias. 

Soil amendment also includes changing up the texture. Hard-packed clay is nearly impossible to grow many plants in, as they have a hard time pushing roots through the tight particles. Mixing in coir is a good choice in these situations, as the coconut fiber-based additive improves porosity and encourages healthy water flow. 

For sandy, loose soil, adding organic matter is key to getting a good consistency and texture. Whether you choose peat moss, coir, compost, or a store-bought blend, till it into the soil carefully and add more every year to ensure there are enough nutrients to support plant life. 

Having healthy soil can make all the difference in your garden, whether it’s in your yard or in a container. While it might take a little extra work, increasing the health of your soil will help benefit your gardening and landscaping projects in the long run.