The Vital Role of Soil in Sustainable Ecosystems

Midori Sakura, Cascadia Community College

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In this natural science lab, students examine different soil profiles along a hillside. Observations are collected about various soil horizon attributes, including master horizon, dominant soil texture, Munsell color, relative degree of compaction, and relative root concentration. Students then compare depths and color of A horizons with a particular emphasis on the soil forming factors of topography and biotic component. Information is then related to topsoil formation and conservation as it relates to sustainable agriculture and carbon sequestration and its importance in mitigating climate change. A specific focus is centered on topsoil depths and factors that affect formation and sustainability of this vital layer.

Learning Goals

The overarching goal is for students to consider and evaluate the vital role that soils have in ecosystem and societal health.

Students will consider the following specific concepts:

- The soil is a finite resource that takes a long time to form

- The topsoil layer in which to grow crops is usually a thin and fragile layer of the soil system

- Soils are extremely diverse, even within a small area

- Soil degradation (in particular topsoil loss) has greatly impacted the sustainability of societies

- Issues of soil sustainability and degradation are often dealt with differently in developed and developing countries

- The degradation of this physical resource affects current social issues, such as desertification and the subsequent migration of people that often causes civil strife

- Maintenance of soil organic carbon is vital in mitigating carbon dioxide effects that contribute to climate change

Context for Use

This activity would be appropriate for any introductory class in natural science that introduces students to soil (i.e. environmental science, physical geography, earth science, ecology, soil science, etc.).

There are a number of different scenarios for which this activity could be applied. Field experience is invaluable if possible for students to observe and learn soil properties that are rather abstract in a textbook and usually have not been directly (or easily) observed by most people. Thus, detailed instructions are provided for the "Field Lab with Instructor Present" in this activity. Though this exercise could conceivably work with detailed color pictures of soil profiles within a classroom, I have found that students benefit greatly from the tactile experience of picking up the soil and feeling the "texture" and noticing first-hand the color of horizons, etc. This lab is wonderful for incorporating different learning styles. Alternative scenarios however could be used for online classes or when a field site is not available.

Best Scenario- Field lab with Instructor Present

Students directly observe soil pits along a topographic gradient at different landscape positions with instructor present. The lab can be accomplished with predug holes (such that at least two to three horizons are revealed) in 1-1.5 hours.

Alternative #1 Students observe road cut with or without instructor present.

Alternative #2 Students observe color pictures of soil pits with horizons or road cut along a topographic gradient.

Description and Teaching Materials

See attached file called "Description and Teaching Materials"

Description and Teaching Materials for Soil Development (Microsoft Word 47kB Jul27 12)

Teaching Notes and Tips

This lab very importantly illustrates that the soil is "part" of an ecosystem; it influences other aspects of an ecosystem and is in turn also influenced by it. Usually, the soil is just "dirt" and most people do not give much regard to the vital component under their feet as being exceedingly important and part of what makes up an ecosystem. The soil is also often labeled as only being "inorganic" or "abiotic" by students. Soil is a complex medium hosting a unique biotic community, in particular, fertile topsoil horizons. Thus, being exposed to a resource that is both "abiotic and biotic" and "inorganic and organic" is usually a new concept.

Though descriptions of soils as published in a soil survey are very descriptive and utilize specific soil terminology, they can also be overwhelming. However, I have had great success in exposing students to basic terms such as master horizons and what general colors of soils can be interpreted to mean.

Students (and the instructor) will get dirty during this lab - remind the students to wear clothes that they don't mind getting dirty.

Ideally, small groups of 3-4 can work as a team to collect data at each pit. Larger groups tend to crowd out the soil pit as usually only one person can sit in a pit at one time.

The only specialized equipment is Munsell color books (single pages can be ordered instead of the entire book). If only purchasing single pages, it is recommended that the instructor research common colors in that region through a soil survey (10YR is often a common page to utilize).

An introduction to soil forming factors, master soil horizon characteristics, and the usage of the Munsell book are necessary prior to this lab.

While observing differences at an undisturbed site will reveal differences in the depth of the A horizon, comparison (or at least discussion) of what happens with disturbance (i.e. construction that involves scraping the topsoil off or paving) is highly relevant to the fragility of topsoil in human-altered societies.


- Suggested Pre-lab questions:

1. What is the difference between a "soil horizon" and a "soil profile"?

2. What is humus and what horizon(s) is it most likely to be in?

3. What horizon is considered the topsoil? Briefly describe two typical features of this horizon.

4. What horizon is considered the subsoil? Briefly describe two typical features of this horizon.

5. What are the five soil forming factors? Briefly explain each factor.

Suggested Questions for Field Site:

1. Evaluate each landscape position and document your observations using a soil profile drawing and text. Use the following soil profile drawing and insert the following characteristics: depth of horizon, horizon label, soil texture (sandy, silty, loamy, or clay) Munsell color (Munsell notation and translated color), relative degree of compaction, horizon where roots are concentrated, and any other notable characteristics (i.e. rocks). Explain why you differentiated the horizons as indicated. In other words, if you had one A horizon and two B horizons, what characteristics did you use to differentiate them?

In order to encourage different learning styles and artistic outlets, I allow students to draw, paint, and even smear the colors of the soil onto the paper.

2. What does the compaction and root concentration indicate about water infiltration and aeration at this location?
- Reflective short essay questions are posed for the student to consider how abiotic and biotic factors influence soil development.

3. Color is a strong indicator of many things in the soil. How does the color and depth of the topsoil differ between the different locations? What soil forming factors would be the most influential in forming the layer?

4. Imagine you are a farmer. Which soil/landscape location would you rather have as the dominant soil type on your farm for growing agricultural crops? Consider the soil properties/data that you collected to substantiate and EXPLAIN your answer. Incorporate at least two different pieces of information that you collected during the lab that justifies your explanation (thus, utilize information from your profile drawings).

5. How has topography and compaction (thus use information from questions #1-2 soil profile drawings) influenced water flow and thus the support of autotrophs at each site? Which site has a greater level of biodiversity (consider the 'biotic community')?

6. What horizon is the most important for the storage of organic carbon and why? Which location is likely to be the most important for organic carbon storage - explain two specific observations you made during lab that support this explanation.

7. Reflect on what you observed during this lab. Prior to this lab, what were your thoughts about soil variability and diversity (particularly within small areas)? After completing this lab, have your thoughts changed? Explain.

Suggested Questions for Sustainability Applications:

1a. [Provide a map on broad global climate patterns] Consider how climate influences soil development. Based upon global climate patterns, which areas of the world are more likely to have older soils in regards to soil development (thus, not necessarily in absolute terms, but relative)?

b. As climate is so influential in soil development and vegetation growth, which areas of the world are more likely to have more fertile soils and thus have a more inherent capacity for agriculture sustainability?

2. Though desertification is not a well-known term, the consequences have wide-reaching social and environmental consequences. What is desertification and why has the UN gotten involved with this issue (UNCCD)?

3a. [Provide map for Global Desertification Vulnerability and Global Climate Map] Why are certain areas of the world prone to desertification?

b. Developing and developed areas of the world have different capacities and resources to address desertification. How do developing and developed countries differ in addressing desertification?

4. a. Though there are many factors that influenced the demise of past civilizations, the sustainable usage of soil and land resources has often been overlooked until recently. How have human actions contributed to past civilizations losing the ability to provide food for their citizens, thus increasing civil strife and war?

b. How are human actions affecting the sustainability of current soil resources in providing food (consider both urban and rural uses of land)?

c. Reflect on the statement, :Those who cannot learn from history are doomed to repeat it." Do you think human societies have learned from history about what a sustainable agricultural system requires? Why/Why not?

5. What is "prime agricultural land" and why is there a growing movement to preserve these types of land? Are there any advocacy groups in your area working to preserve local areas of prime agricultural land?

References and Resources

Brady, N. and R, Weil. 2007. The Nature and Properties of Soils. Prentice Hall, New Jersey.

Egan, T. 2006. The Worst Hard Time: The Untold Story of Those Who Survived the Great American Dust Bowl. Houghton Mifflin, New York, New York.

Hillel, D. and C. Rosenzweig. 2009. Soil Carbon and Climate Change [Online]. Available at CSA News 54(6):4-11.

Montgomery, D.R. 2007. Dirt: The Erosion of Civilization. University of California Press, California.

Natural Resources Conservation Service. 2012. Guide to Texture by Feel. Available at (accessed 12 Aug 2012). USDA-NRCS, Washington DC.

Natural Resources Conservation Service. 2012. Web Soil Survey. Available at (accessed 12 Aug 2012). USDA-NRCS, Washington DC.

Natural Resources Conservation Service. 2012. World Soil Resources Map Index. Available at (accessed 12 Aug 2012). USDA-NRCS, Washington DC.

United Nations Convention to Combat Desertification. 2012. United Nations Convention to Combat Desertification. Available at (accessed 12 Aug 2012). United Nations (UNCCD), Germany