Study Questions – Soil Organisms

1. According to your textbook, what are the numbers of various soil organisms that might be expected in a gram of an A horizon?

2. In a tropical rain forest, it has been said that there is more biodiversity in the soil than in the forest itself. What is meant by this?

3. What are some of the ecosystem processes that are performed by the various soil organisms?

4. In the soil food web, what is meant by a producer vs. a consumer?

5. Give some examples of macrofauna and their role in soils.

6. Explain how earthworms influence soil properties.

7. What is the rhizosphere and how does it differ from the surrounding soil?

8. What is the general role of soil microbes in soils?

9. What is nitrogen fixation and what organisms are responsible for it in soils?

10. Why are fungi important in forest ecosystems?

11. Explain what mycorrhizae are and how they are beneficial to plant growth.

12. Under what soil conditions (i.e. moisture, temperature, pH) would you expect to find the greatest microbial activity?

Soil Organic Matter

1. Explain the role of vegetation in the formation of soil organic matter.

2. Describe some of the benefits that soil organic matter provide to soils.

3. What kinds of materials collectively make up soil organic matter? What is humus?

4. Draw graphs to illustrate how microbial activity is affected by soil water content and soil temperature.

5. Explain the difference in soil organic matter accumulation in grassland vs. forested ecosystems.

6. What are some of the factors that influence how rapidly organic residues are decomposed in soils?

7. Consider a grassland soil in North Dakota and one in New Mexico. Assuming both soils receive about the same amount of annual precipitation, which soil would contain the most SOM? Why?

8. Consider a grassland soil in eastern Colorado and one in eastern Iowa. Assuming both soils have about the same annual soil temperature, which soil would contain the most SOM? Why?

9. Why are wetland soils often Histosols?

10. List some of the reasons that SOM levels decrease rapidly in soils that are put into cultivation.

11. What are the major groups of microbes involved in decomposition of organic residues?

12. What is composting and what are some of the benefits?

13. What conditions are required for composting?

14. During the composting process, explain what happens to C:N ratios of composted residues. Why?