Relative Soil Particle Sizes. Source: The Disovery Channel

Since gravel is larger than 2 mm in diameter, it is not considered a soil particle. Another good visual description is to consider a beach ball as a sand particle, a silt particle as a baseball, and a clay particle as a BB. That would be roughly the relative sizes of each particle if they were enlarged.

Soil scientists classify soil textures into 12 soil texture classes as shown in the soil texture triangle:

Soil Texture Triangle. Source: USDA

As an example, say we have a soil that is 45% clay. So we move up the left side of the Triangle until we get to the 45% line (numbers align with their respective lines). This soil is also 30% sand so we move from the right side to the left along the bottom axis until we get to the 30% sand line. The point where the 45% clay and the 30% sand lines intersect lies within the boundaries of the clay loam soil texture class. We can follow the silt percentage line to find that we have 25% silt. Since the sum of each should add to 100% we can also find the silt proportion by difference (100% – 45% – 30% = 25%).

Soil scientists measure soil texture by a variety of methods. The most common for everyday use is the texture-by-feel method which can be done using the following chart (click to enlarge):

Soil Texture by Feel Flow Chart. Source: USDA

It is just like any other dichotomous key with a series of yes/no questions. It doesn’t really give an exact percentage of the sand, silt, and clay, but gets the scientist “in the ballpark” of what the soil texture class should be. UC Davis put out a great video on how to do texture by feel:

Texture by feel is useful in the field. It does take lots of practice to “calibrate” your hands with soils of known textures. Some tips that I’ve learned along the way are the following:

• Mica in the sand-sized fraction can act like clay making long ribbons
• Silt feels like baking flour
• Expansive clays may lead longer ribbons and overestimation of clay content

Another method that is commonly used is the hydrometer method, which is a more reliable, repeatable, and unbiased method than texture by feel, thought it takes much longer. The same UC Davis group also made a great video on how to determine soil texture by the hydrometer method:

The chemical they use is a dispersant which chemically breaks up any soil peds or aggregates.

Soil texture is more than just how the soil feels to you or me. Soil texture is important because it is one of the principle properties of soils. Texture effects on how fast water can move through soil, erodability, retention of nutrients for plants and microbes, the microbiol community makeup, bulk density, and with all of those properties, what ecosystems or cropping systems can exist on that soil.

Since soil texture is so important, I’ll be referring back to this post regularly in future blog posts.

At each of the sites where we stopped, all of the students broke out into six groups and worked to describe and classify the soil at their assigned location. My job was to bounce around from group to group to answer any questions and help walk them through the Keys to Soil Taxonomy as they classified their soil. I also helped a little with the discussion at each stop.

Here are some pictures I took along the way…

The Wright Brothers Memorial

Our first stop on the trip was to the Wright Brothers Memorial at Kitty Hawk, NC. This memorial commemorates the first ever self powered flight. It’s also located on a huge dune that overlooks all of the development in the area. There were several soil science concepts we covered here, including the form of the large wind-blown dunes on the outer banks, desication of plants (trees especially) due to the wind and salt and how that affects what plants can grow in this environment, the availability of drinking water on the outer banks, and how growth was limited on Kitty Hawk and Nags Head by the city not developing a public sewage system (the property owners can only build a house as big as their septic system can handle… thus no 8 story condos).

The Wright Brothers Memorial Dune

We then moved on to the beach. The North Carolina Outer Banks are a system of islands that move seaward or landward depending on sea level (on a geologic time scale). Currently the islands are moving landward with ocean level rising since the last ice age. However, that doesn’t stop people from developing the outer banks with multi-million dollar homes that are rented to tourists. These houses are annually at risk of being washed into the ocean.

A house that almost fell into the drink is now protected by “beach renourishment”. Would you buy a house here?

However, through successful lobbying, the State of North Carolina and the federal government have stepped in to pay for “beach renourishment, which is the act of dredging sand from 2 or 3 miles off the coast, and blowing it back on to the beach. This in turn protects the houses for as long as the sand  lasts. It is constantly being eroded, so it will take another huge influx of taxpayer money in a few years to protect these million dollar homes.

The Soil Geomorphology class looks on as the “beach renourishment” sand erodes back into the ocean.

As a soil scientist, I think that it is unwise for the government to pay to protect million dollar houses, or any houses for that matter, on land that will inevitably be eroded away by beach erosion some day, nor should it fund the construction of cities in annually flooded areas. I think it’s more logical to let nature run its course most of the time and not build permanent structures on non-permanent landscapes.

The “beach renourishment” added about 200 meter wide strip of sand to this beach. Beforehand the beach was literally underneath the stilts of the houses.

That was it for the first day. Most of the first day had been taken up by the 4 hour trip from Raleigh to the outer banks.

On the second day we first stopped at Nags Head Woods to look at soils in a Maritime Forest. We then went to Manteo to look at a variety of Spodosols (an order of soils that develop in sandy areas under pine forests, pictured below).

Spodosols at Manteo, NC

After that we went on to the mainland where we stopped at Somerset Place on the shore of Phelps Lake, which was once one of the biggest plantations in the state of North Carolina with an area of 100,000 acres. Somerset place had over 800 slaves, cumulatively, and a peak area under production of around 8,000 acres. They grew rice, corn, wheat, and more. They also planted some amazing bald cypress trees as you can see with my picture below. By the way, bald cypress are the species I research for my graduate work.

Colby standing next to a bald cypress tree (Taxodium distichum) at Somerset Place.

We did one more stop on the shore of Phelps Lake. Phelps Lake is a pocosin lake. Pocosins are swamps that form on lands that are very wide (on the order of many miles), and very flat (as in flat as a pancake) where the source of water is rainfall, and the water cannot drain fast enough so it only leaves via transpiration. Over time these wet conditions allow for the accumulation of plant matter to create Histosols. The swamp that forms is actually the highest point on the landscape, thus bringing us to the term “pocosin” which is Algonquin Indian for “swamp on a hill”. When lakes form on these pocosins, they are termed pocosin lakes. These are the only naturally occurring lakes in the state of North Carolina.

Dr. Lindbo explaining how pocosins and pocosin lakes form.

Cypress trees growing on the organic soil shore of Lake Phelps

We dug some profiles in the Histosols around the edge of the lake so that everyone there could see and feel organic sols.

Histosols near the edge of Lake Phelps

Our last stop was to look at some lower coastal plain Ultisols at the Vernon James Tidewater Research Center (an extension and research farm for NCSU).

Vernon James Center Ultisols

After that Alan Meijer, a PhD student and extension agent for the NCSU Dept. of Soil Science gave us a tour of the different tillage, planting, and harvesting equipment used on the research farm.

Alan Meijer presenting tillage equipment

We ended the long day with pizza and a presentation from Paul Lily, Soil Science Professor Emeritus, on the history of North Carolina with a soils and agriculture perspective.

On the third day (and last day for me, I had to get back to Raleigh to do real work) we made our way up the coastal plain and back to Raleigh. The coastal plain is an area along the Atlantic coast of the US that consists of marine, and alluvial sediments (sediments deposited by the ocean and by rivers). The oldest parts of it are at about 300 feet elevation, the youngest parts are at the beach. We stopped to look at some scarps (abandoned beaches from times of higher ocean levels), some flood plains, and some toposequences (we examined soils along a hillslope to see how topography affected the soils).

Some Tupelo Gum trees in the backswamp of the Tar River floodplain

Soil profiles along a toposequence in the Coastal Plain.

A gully that was down-cut since settlement of North America has exposed a nice soil profile of a Grossarenic Hapludult.

That’s pretty much it for the leg of the trip in which I participated. I did do the full trip as a student the last time the course was offered (in 2010). If you would like to read about that adventure you can read about it on my personal blog here. All of the pictures from this trip are available on my Soil Geomorphology Tour 2012 Picasa Album. Pictures from the entire week’s trip from 2010 are available on my Soil Geomorphology Tour 2010 Picasa Album.

I encourage you to take a few minutes this week to contemplate just what soil and water stewardship means to you, and perhaps what you can do to do more.

I am not able to imbed the video directly on this page, but the following tweet was sent out by the governor with the link to the Youtube video:

@brianschweitzer Watch Governor Schweitzer on the Late Show with David Letterman http://www.youtube.com/watch?v=lDErImLB0yA&feature=youtu.be

For those soil scientists and agronomists out their, I’d definitely recommend listening to at least the first 3 minutes of the interview. It’s great to hear what we do be discussed on a TV show with millions of viewers.

Gov. Brian Schweitzer, Photo: Wikipedia

I don’t plan to ever become political in this blog (except in the defense of science and science funding when needed), but I was impressed with the governor… but again I might be biased being that he is a soil scientist after all.

Interesting Links:

Gov. Schweitzer’s Twitter

Gov. Schweitzer’s Website

Gov. Schweitzer’s Wiki Page

The Late Show

Histosols

clayey, kaolinitic, dysic, isohyperthermic Terric Haplosaprist; Photo: SoilScience.info

Histosols are soils with organic matter as the primary parent material. They occur when conditions allow organic matter to accumulate at a faster rate than it can be decomposed. This is usually under wet conditions such as a wetland (think the Florida Everglades) or in areas where it’s just too cold for the microbial community to decompose plant material fast enough (think the Arctic Circle).

Histosols have organic surface layers at least 40 cm deep that are at least 12-18% organic carbon (not living roots) depending on clay content. Some frozen soils that were once classified as Histosols have been now reclassified as Histels once the Gelisol soil order was introduced.

Histosols occur where wet conditions exist because saturated conditions don’t allow air (and oxygen) to enter the soil profile, thus eventually creating anaerobic conditions. Under these conditions decomposition or organic matter is slowed, and what would have been converted into carbon dioxide by microbial respiration in dry conditions instead remains in the soil as organic matter. This organic matter builds up over time and eventually forms a Histsol.

There are different types of organic soil materials including fibric, hemic, and sapric soil materials. Fibric soil materials are organic soil materials that contain three-fourths or more plant fiber material after rubbing [to soil scientists, rubbing means rubbing the material between two fingers 10 times]. Sapric soil materials are organic soil materials that contain less than one-sixth plant fiber materials by volume after rubbing. Sapric materials will feel “greasy”. Hemic soil materials are in-between fibric and sapric.

Suborders

For Histosols, the formative element for the order is “ist”. As described by Buol, et al (1997) Histosols have five suborders and they are classified in the following order in Soil Taxonomy. Wassists are Histosols that are floating on top of free water. Folists are Histosols that formed not due to wet conditions, but from high rates of accumulation of organic matter (relative to decomposition). The rest of the suborders are classified based on the state of decomposition. Fibrists are Histosols with fibric materials, Hemists are Histosols with hemic materials, and Saprists are soils with sapric materials.

Occurence

As said above, Histosols form anywhere that has a rate of organic matter accumulation greater than decomposition.

Photo: USDA NRCS

At the scale of this map, it’s difficult to pick out many expansive areas of Histosols. However, they do occur throughout the world, but usually in small areas. This map of the US shows a better depiction of their occurrence.

Photo: USDA NRCS

Uses

Histosols are used for crop production and forestry, as well as wildlife and recreation. The organic material can also be harvested for horticultural potting soil and for heating and electricity. They can be production crop soils, however extensive drainage is required.

Unfortunately, drainage leads to subsidence. Subsidence is the loss of soil depth. Subsidence occurs when water is drained from the profile. The organic materials “float” in saturated conditions and become more compact when drained. Once drained, the soil begins to oxidize and microbes consume the organic matter and slowly turn it into carbon dioxide with time. Subsidence, as a rule of thumb, occurs at a rate of 1 inch of soil per year. This creates problems for drainage ditch maintenance and long term uses of agricultural soils.

Depth of Subsidence; Photo: USDA NRCS via University of Idaho

Histosols, when drained, are also vulnerable to fires. Here is a recent news story about a fire that occurred in Alligator River National Wildlife Refuge here in North Carolina <http://outerbanksvoice.com/2011/06/10/million-of-gallons-of-water-pumped-on-peat-fire/>. 

Histosol Fire, Photo: The Outer Banks Voice

Here’s an excerpt from that article:

Flammable organic peat ranges from a few inches to 8 feet deep in the ground, said the multi-agency team fighting the fire.

Because of the lack of rain, peat, which was once used as a fuel, continues to burn even when the surface fire is put out, according to the North Carolina Incident Management Team.

“The ground fire will continue until the fire consumes all the peat down to mineral soil, the fire burns down to a level of high moisture content, or the soil moisture level rises to the fire as a result of an extended heavy rain or pumping operations,” the team said in a statement Friday.

Histosol profile; Photo: USDA NRCS

My current research involves Histosols in a Carolina Bay wetland. The wettest part of the wetland (the center) is where the Histosols occur. They’re really interesting soils (I might be biased because I’m a wetland soils guy).

Some good Histosol info sources:

The USDA NRCS

Wikipedia

Buol, S., et al. 1993. Soil Genesis and Classification

Previously discussed soil orders:

Gelisols

Photo: NASA

Happy Earth Day everyone.

Earth Day is a holiday celebrated by people of all walks of life in a variety of ways. In the past I’ve celebrated it by doing trash clean-ups, educating the public about water quality using an ISU SWCC groundwater flow model, and more. I’m not planning any environment-related activity for today outside of this blog post and a long dog walk on a greenway trail, but I do participate in a variety Earth-friendly activities throughout the year.

If you’re planning some Earth Day activities, I encourage you to first read about the interesting history of how it started on the Earth Day Wikipedia page.

Here’s a couple of soil and water-friendly activities I suggest.

Build a rain barrel

Rain barrels are tanks that store rain water from a gutter downspout and saves that water for non-drinking water uses like watering garden plants. They can be constructed through mostly reclaimed products like used pickle barrels. There are multiple “how-to” videos on Youtube that will show you how. You can pick up a pickle barrel for $10 or $15 on Craigslist. They’re easy to build, and can be built for around $40.

Participate in a litter clean-up

Many organizations and municipalities will organize litter clean-ups. Litter clean-ups are easy, and are a very common Earth Day activity. Some places to find one that’s already organized include your local County Soil and Water Conservation District, the River Keepers, your local municipality, listings in your local newspaper, etc. For those of you geocachers, Geocaching.com has some CITO (Cach In Trash Out) events, in which many people focus on a local park, river corridor, etc and go geocaching in the area while carrying trash bags. Participants then remove any litter they come across along their way.

Start a garden

Gardens are a lot of fun. There’s also a sense of accomplishment when you can make a meal with food that you raised from seed. Gardener’s gain a sense of appreciation for soil and also where their food comes from. In addition, growing your own food cuts down on your carbon footprint by eliminating the transportation of the food that you grew, but would have bought from your local market.

Build a compost bin

If you are already a gardener, one way to cut down how much trash you create while adding nutrient rich material to your flower bed or vegetable garden is by composting all of your organic wastes (wasted food, newspapers, etc.). You can build a compost bin in your back yard as a weekend DIY project. Vermi-compost is also an option, which is where you compost paper and some food waste by letting worms “process” the waste. Once again, Youtube is a good resource for “how-to” videos.

Think of some lifestyle goals that are Earth-friendly

Earth Day is a good concept, but the message is lost if people are only Earth-friendly one day of each year. Some goals for a year-round Earth-friendly life style might be to:

• Ride your bike or walk to work/school a few days a week
• If biking/walking is an option, carpool to work/school
• When shopping, choose “local” products with less packaging
• Water your plants with used dishwater
• Take short, warm (not hot) showers

Lastly, I just want to note that the Soil Science Society of America (SSSA) is relaunching their “I Heart Soil” campaign today. I encourage you to visit the campaign website and ”like” their Facebook page, 

The four Land Grant University agricultural deans who authored "No Limits to the Value of an Agricultural Degree".

Luckily, the article has been pulled apart by the scenes by countless people in the agriculture and education professions. One counter was written by four deans of agriculture colleges at four major land grant universities (including a dean from my Alma Mater, Iowa State University) – No Limits to the Value of an Agricultural Degree. The article outlines the real outlook on agriculture degrees and explains how the job outlook for agriculture, animal , and natural resource scientists not only good, but there is a huge shortage in people with training in these fields. Unemployment for those disciplines is very low even in the current recession, and that unemployment is projected to be low at least for the next decade due to the demand of people with these so called “useless” majors.

A second notable counter to Mr. Loose’s article has been offered by an advocacy group called Farmers Fight, which was started by students at Texas A&M. They maid a great video to get the message out:

The video does a great way of succinctly expressing the inherent value of several major agricultural degrees in a way that shows how agriculture is relevant to even those who live in an urban setting. Farmers fight also has a blog, a Twitter feed, and a Facebook page if you would like to follow the effort. Please spread this video and help to make it go “viral”.

My take is this: everybody eats, we have a growing human population, there is only so much arable land on planet Earth. You tell me how “worthless” a degree may be from the agricultural sciences.

This book does a great job of capturing every angle of the dust bowl. In writing the book, Eagan focused on the individual stories, and even quotes personal diaries. He also touches on the local, state, and national politics that occurred during that time during the Hoover and Roosevelt administrations. He explains the goals of different conservation efforts put into place for relief such as the soil conservation efforts lead by Hugh Hammond Bennett, the projects installed by the CCC, and the creation of the Soil Conservation Service (now the Natural Resource Conservation Service).

Photo: USDA ARS

The book, in my opinion as a soil scientist, and as an empathetic Midwestern farm kid, does a great job depicting the struggles farmers went through in that time, and the difficulties that farmers and government can have in efforts to stop erosion. I recommend this book to anyone who is interested in soil and environmental science, policy, drama, country living, and more. I gave it 5 stars on my Amazon Kindle review. Let me know what you think of it in the comment section below.

As this is my first book review on ColbyDigsSoil, I am starting a new rating system. I give this book 5 shovels.

Useful links:

• Publisher’s website
• Buy it on Amazon
• Wikipedia article on the dust bowl

Gelisols

A picture of a Gelisol profile. Photo: SoilScience.info

Gelisols, in a nutshell, are soils that are frozen. They are soils that have permafrost (frost, i.e. frozen soil, that is present year-round) within 100 cm of the soil surface, or have “gelic” material within 100 cm with permafrost within 200 cm of the surface. Gelic materials are mineral or organic soil that is present due to “cryoturbation”, or churning of the soil profile due to freezing and thawing.

Suborders

As described by Buol, et al (1997) Gelisols have three suborders including Histels, Orthels, and Turbels. [A quick note on how Taxonomy works. The formative element attributed to the soil order, in this case 'gel' from GELisols, always occurs at the end of the soil classification.] Histels are Gelisols that have a lot of organic matter incorporated into the soil profile. They often occur in low lying, or wet areas. Turbels (from the Latin, turbides, “disturbed”) are Gelisols that are characterized by evidence of Cryoturbation. That means that they have one or more soil horizon that is irregular, broker, or distorted due to action of freezing and thawing. Orthels (from the Greek, orthors, ”true”) include all other Gelisols that do not have high amounts of organic matter, or show low evidence of churning.

Characteristics

Gelisols can be very old soils. However they usually don’t exhibit much in terms of soil development due to short growing seasons, cold temperatures, limited plant growth, etc. An expert in Gelisols, Chen-lu Ping, from the University of Alaska Fairbanks can be seen in the next picture using a gas-powered jack hammer to “dig” a soil profile.

One thing that is interesting about Gelisols is that in some landscapes, they create a hexagonal pattern caused by the expansion of ice in cracks as shown in the following picture.

Gelisol landscape. Photo: Wikipedia commons

Occurance

Gelisols, as you can imagine, occur in areas where it is cold. For my US readers, you’ll only find them in Alaska.

Distribution of Gelisols. Photo from University of Idaho

US Distribution of Gelisols. Photo from US EPA

A picture of a Gelisol soil profile, and the landscape from which is was sampled. Photo: SoilScience.info

Use

In order to use Gelisols for human uses, many precautions need to be made – mostly to ensure that the permafrost stays frozen. This would be precautions like putting buildings on stilts so that the air directly above the soil stays cold, avoiding leaving open holes in them so that they don’t thaw out from the exposed soil profile, etc. Generally they are best left wild, or used for habitat. Wildfire and human activity can cause permafrost retreat, and  as Buol et al (1993) puts it, “change a nearly level terrain into a hilly thermokarst one”.

Good sources for further information

USDA Natural Resource Conservation Service

Wikipedia

Buol, S., et al. 1993. Soil Genesis and Classification

Thanks Jess for the feature!