Unit 7.2 - Agricultural Impacts

Susan Gill (Stroud Water Research Center) and Ashlee Dere (University of Nebraska - Omaha)

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Summary

Humans not only reside in the Critical Zone, they depend upon the land and water to provide sustenance. This unit will examine how humans affect soil resources and ecosystem services in the Critical Zone through food production. In addition, it will discuss farming practices that led to the Dust Bowl in the 1930s. Finally, it will examine emerging efforts to grow food locally such as Community Supported Agriculture (CSAs) and urban gardening programs.

Soils, Soils and Agriculture, Sustainability, Ecosystems | College Lower (13-14), College Upper (15-16)

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Learning Goals

Students will be able to:

Identify how food is grown in various contexts, such as industrial agriculture, family farms, organic agriculture, community-supported agriculture, and urban gardening
Analyze how each of the above types of food production and the practices employed by various individuals and organizations affect soil and water resources
Describe the causes that resulted in the Dust Bowl and the social, economic, and environmental impacts that resulted
Analyze how current farming practices affect carbon storage in soils
List the benefits of ecosystem services to society and describe how a critical zone perspective can help assess these services

Context for Use

This unit is classroom-based and is best used as a set of group exercises, where students will report findings/ideas back to the class for discussion. The content can be modified to use either in an introductory undergraduate environmental course or in an introductory course on Critical Zone processes for geoscience majors. It is designed to be accomplished in three hours of instruction. It does require homework that should take approximately six hours. Students will be asked to read the chapter entitled "Dust Bowl" in Dirt, the Erosion of Civilization, as well as use web library resources to complete their assignments. In addition, students will be asked to interpret Critical Zone data from a journal article to compare characteristics on soils between two sites: agriculture and forest. The data include bulk density and organic carbon content information by soil horizon between two sites, one of which is an agriculture site and the other a forested site. Students will also be asked to complete a worksheet and prepare a short paper, which may be a group exercise if the class is too large.

Description and Teaching Materials

There are several projects in this unit that can be completed in class or as homework, depending on the amount of time the instructor wants to dedicate to this unit. The activity that evaluates different kinds of agriculture can be completed as individual or group projects depending on class size. Students should complete the Agricultural Techniques worksheet based on their research that can be shared with the class. The content of the student research will then form the basis of class discussion. Except for the soil carbon exercise, all of the activities in this unit are based on readings or student research, and class time is best used for discussions based on the readings and research; thus, students are expected to complete several tasks prior to class to prepare for the group discussions. It is recommended that students meet in small groups initially to compare results of their reading and research before bringing the class together for larger group discussion. If time permits, the unit can be covered over two days, with a focus on the different means of food production the first day and then soil organic carbon the second day. The soil carbon activity can be completed using pre-graphed data, but raw data is also available for more advanced students to continue practicing Excel skills and more advanced calculations of carbon storage. The activity can also be assigned only as homework, although students benefit from discussing results as they work through the activity.

Pre-class Readings/Research:

Field, J. P., D. D. Breshears, D. J. Law, J. C. Villegas, L. López-Hoffman, P. D. Brooks, J. Chorover, and J. D. Pelletier (2016), Understanding ecosystem services from a geosciences perspective, Eos, 97, doi:10.1029/2016EO043591. This brief article describes some of the benefits society receives from ecosystems and how Critical Zone Science can be used to understand the value of such services at multiple scales.
Dust Blow, Chapter 7 (pages 145-178) in Dirt, the Erosion of Civilization by David R. Montgomery - This chapter describes the causes of the Dust Bowl as well as similar situations that have occurred as a result of human mismanagement of soil resources in other locations.
- Students will prepare a 1 page typed (single spaced) summary of the causes and impacts of the Dust Bowl. The report should outline potential ways to address the issues raised in the book chapter. In addition, students should address the concept of ecosystem services and how society benefits from ecosystems. Fully cite any outside sources.
Agricultural techniques research: Task each student with researching one of these agricultural enterprises (international agribusiness, industrial agriculture, small/family farm agriculture, community-supported agriculture, organic agriculture, or urban agriculture). Have them outline the characteristics, benefits, and impacts of these various types of agriculture and use the guiding worksheet to compile information. Results from their research will form the basis for an in-class discussion. Suggested links are listed below.
- Agricultural techniques research worksheet Agricultural Techniques Worksheet.docx (Microsoft Word 2007 (.docx) 12kB Jan19 17)

Unit 7.2 (Day 1)

Group Discussion - Different Means of Food Production (25 min)
- Have students assigned the same farming technique meet in small groups to compare notes from their research. Then have each group summarize their findings, focusing on the characteristics, benefits and impacts of the various types of agriculture. Once all groups have reported on what they learned, focus the discussion on how the various farming techniques would impact ecosystem services, connecting back to the role that CZ science can play in understanding and quantifying the value of such services.
Activity 7.4: Comparison of Soil Organic Carbon by Land Use (30 min)
- Use data from Christina River Basin CZO soils research (below) to compare and contrast bulk density and organic carbon content of two soil profiles, 1) agriculture site and 2) forested site.
  - Plotted data: Soil Carbon Comparison comparison_soil_carbon_soils.docx (Microsoft Word 2007 (.docx) 251kB Jan19 17)
  - Worksheet: Soil Carbon Comparison Comparison of soil carbon in soils by land use (Microsoft Word 2007 (.docx) 18kB Dec26 16)
  - Data: Soil Carbon Comparison (Yoo et al., 2011): Soil Carbon Data (Excel 2007 (.xlsx) 9kB Jun2 16)
  - KEY: Soil Carbon Comparison Data:
    KEY Soil Carbon Data -- private instructor-only file
  - Yoo, K., Junling J., Aufdenkampe A., and Klaminder J. 2011. Rates of soil mixing and associated carbon fluxes in a forest versus tilled agricultural field: Implications for modeling the soil carbon cycle. J. Geophys. Res. 116:G01014. doi: 10.1029/20102JG001304
- Students work in groups of 2-3 to discuss what this data means, but work independently to plot and write up results.
Group discussion - Dust Bowl impacts (20 min)
- Discuss the main points from the Montgomery reading on causes of the Dust Bowl and where and why similar events have occurred globally. Focus on the root causes of the Dust Bowl, especially the role that humans played, using a systems approach to emphasize why conservation measures were or were not implemented. Discuss implications of such actions on ecosystem services and how soil loss could impact both ecosystem services and society. Have students suggest possible solutions to soil loss and how CZ Science could help identify possible solutions.
Homework:
- Complete the soil carbon comparison worksheet if not finished in class. (36 pts)

Teaching Notes and Tips

There are several projects, such as the evaluation of different kinds of agriculture, that can either be done as individual or group projects. These should begin with the completion of the agricultural techniques research worksheet that can be used as a guide for reporting back to the class, and a reference sheet for students to keep notes as other groups present. If this is done as a group project, it may be best to keep the group size to two or three to assure that it is more difficult for someone to be a "free rider," even if this means that there is more than one report on a specific topic. In that case, provide time for groups to meet and compare notes before beginning class sharing and discussion. Students may rely heavily on preconceived concepts of agricultural systems rather than evidence from their research, so the instructor should be prepared to correct or point out these biases and should emphasize the need to cite sources. The topic of personal bias and identifying reliable sources could also be incorporated into the class discussion, as their research will likely include a range in source quality. A discussion of the strengths and weaknesses of various sources, and how to filter and evaluate sources, would complement the science communication activity in Unit 6.2.

The exercise on soil carbon could be started in class and finished as a homework assignment. Both a handout with plotted data and an excel file with raw data are provided. Having students plot the raw data and perform some calculations of total carbon storage is recommended for advanced students, especially to help reinforce Excel skills practiced earlier in the curriculum. The worksheet is designed to accompany student plotting and calculations. If students are not comfortable with Excel or if time is limited, the handout with pre-plotted data may work better. If using the pre-plotted data, the word document includes some very basic guiding questions for students to answer about the plots. The provided worksheet could be modified as desired to incorporate more detailed questions regarding the plotted data. Encourage students to reference the primary source article to find context for the data, such as how and where it was collected, when interpreting the results. Regardless of whether data is plotted by students or provided to students, you may wish to go over the results if it appears that students do not understand that forest soil has more carbon and lower bulk density than agricultural soil. Students seem to work well in groups to graph and process the data. A discussion of their findings would be useful at the beginning of the next class period if time allows.

Assessment

Pre/post testing- this will not be graded, but will provide a measure of the effectiveness of the unit, if desired. Students should complete tests online before and after class, if possible.

Pre/Post test::
Unit 2 - Humans in the Critical Zone Pre/Post Test -- private instructor-only file

Different Means of Food Production - Individual or group projects (depending on class size)

Class discussion (6 pts) Class Discussion Rubic (Microsoft Word 2007 (.docx) 20kB Dec26 16)

Causes and impacts of the Dust Bowl

Paper (36 pts) Short Essay Rubric (Microsoft Word 2007 (.docx) 25kB Dec26 16)

Comparison of Organic Carbon in Soils by Land Use from Christina River Basin CZO

Worksheet (36 pts) Short Essay Rubric (Microsoft Word 2007 (.docx) 25kB Dec26 16)

Total Points: 78

References and Resources

Yoo, K., Junling J., Aufdenkampe A., and Klaminder J. 2011. Rates of soil mixing and associated carbon fluxes in a forest versus tilled agricultural field: Implications for modeling the soil carbon cycle. J. Geophys. Res. 116:G01014. doi: 10.1029/20102JG001304
Field, J. P., D. D. Breshears, D. J. Law, J. C. Villegas, L. López-Hoffman, P. D. Brooks, J. Chorover, and J. D. Pelletier (2016), Understanding ecosystem services from a geosciences perspective, Eos, 97, doi:10.1029/2016EO043591. Published on 19 January 2016.
Montgomery, D. R. 2008. Dust Bowl. In: Dirt, the Erosion of Civilization. University of California Press, Berkeley, California. p. 145-178.

Web resources to initiate agricultural techniques research: