Unit 3: Crops and Irrigation Patterns in the United States
This unit is designed to allow students to quantitatively assess how much water is used for irrigating crops and how this varies across the United States. This unit also has students link water use to the economic value of the crops that are produced--spanning the scientific and economic disciplines. The concepts that students learn here will connect back to the Water Footprint concept that was introduced in Unit 2, as students consider the accuracy of water calculators.
Unit 3 is designed to help students advance in achievement of module learning goals 1, 3 and 4:
- Module Learning Goal 1: Explain how freshwater availability and management practices pose threats to ecosystem integrity, human well-being, security, and agricultural production.
- Module Learning Goal 3: Explain what controls geographic variability in irrigation, groundwater mining, and ecosystem impacts of agriculture in the United States.
- Module Learning Goal 4: Apply geoscience information and methods in interdisciplinary assessments of the sustainability of water systems.
The unit also has the following more specific learning objectives.
Upon completion of the unit, students should be able to:
- Relate the spatial patterns of irrigation in the US to geographic precipitation patterns;
- Extract data from data tables and perform basic calculations with it; and
- Integrate quantitative hydrological and economic data to evaluate the if irrigation water is being used for maximum benefit.
Context for Use
This unit has been designed as part of the Water Agriculture, and Sustainability Module 3. It can also be incorporated into an introductory-level Earth or environmental science course. If this is done, students should have a basic understanding of the hydrologic cycle and be familiar with the concept of the water footprint of agricultural products.
The unit can be adapted to many class sizes and formats using the in-class activities. Students will need to complete this unit in order to comprehend and complete Unit 4: Irrigation and Groundwater Mining.
Class Size: This can be adapted for a variety of class sizes.
Class Format:The activities in this unit are suitable for a lecture or lab setting or as a homework assignment. If done in class, students can work in groups of 2-4 and the instructor can hand out hard copies of the materials. Some of the USDA crop data is available on-line so students should have access to the internet. Students can work together but each student should complete his/her own assignment.
Time Required: The instructor should plan to use two 60-minute class periods or one multi-hour lab session.
Special Equipment: Students should have a computer and access to the internet in order to find data on US agricultural statistics. If that is not possible, the instructor can print out the data before class.
Skills or concepts that students should have already mastered before encountering the activity: Before the class activity, students should:
- Be familiar with the concept of the water footprint of agricultural products.
Description and Teaching Materials
Unit 3.1 Irrigation Patterns(one 60 minute class period)
Activity 3.1a - Pre-class Homework Assignment
Students should read pages 25-27 of Maupin et al. 2014, USGS irrigation info (Acrobat (PDF) 350kB Jun17 16) before coming to class. This will give them some background information on freshwater withdrawals for irrigation and they will be using the data from this in the class exercise. They should be given the assignment to "Describe what the term 'agriculture' means to you with as much detail as possible. Provide a drawing or images that support your description." This will have them beginning to think about agriculture.
There is no assessment for this assignment (you could use a pass/fail grade) but students will share and discuss the definition of agriculture at the beginning of class.
Activity 3.1b - Beginning of Class Mini-Lecture (10 minutes)
The instructor should introduce the following concepts to the students at the beginning of class using the Unit 3 Slides (PowerPoint 2007 (.pptx) 201kB Jan23 17):
- Students should be aware of the differences in rainfall across the United States. This can be accomplished by showing a map of annual mean rainfall (Slide 1). Ask students to look at the map for a minute or so and have them talk with neighbors to describe the patterns, then share with the class (Think-Pair-Share). The instructor may want to prompt the students to note the rapid change/gradient across the Great Plains states.
- The instructor should note the 100th meridian (line of longitude that is the border of the Texas Panhandle with Oklahoma). In general, west of this boundary, irrigation is required to grow cereal crops such as corn and wheat. It is the western boundary of where moist air from the Gulf of Mexico can travel.
- Since students will be working with large volumes of water and the units of acre-feet, the instructor should review the units of volume for water and give them some context for the different units (Slide 2).
- Students will be asked to consider the value of crops and the amount of water used in irrigation. Specifically, if we consider a sustainable use of water, it should be used to generate the highest value. An example would be that irrigating nut trees or strawberries will generate more revenue per acre than a lower-value crop such as alfalfa or hay.
Activity 3.1c - Irrigation and Agriculture Activity (40 minutes)
In class, students will use the provided handout to learn about how much water is used in irrigation for seven states representing the East, Midwest, and West. The attached Word document will lead students through a set of questions and calculations using attached data tables. It is designed for students to work in groups but it could also be adapted for students to do on their own in class or outside of class. If done in the classroom, students will need access to the internet to gather data from the USDA website.
- Divide class into groups of three to four students;
- Give printed copies of the Student Exercise (Microsoft Word 2007 (.docx) 1.4MB Jan23 17) to each student (there will be a blank US map at the end of the packet). You may choose to have students manipulate the USGS irrigation water withdrawal data using a spreadsheet. If so, then download the USGS Irrigation Water table (Excel 2007 (.xlsx) 42kB Jan23 17) ;
- Give each group the Unit 3 data packet (Acrobat (PDF) 369kB Nov9 16) that has the USDA data tables. Hard copies can be printed or have them access an electronic version;
- There are four sections in the lesson. The idea is that the students work independently to complete each section and then the group discusses their answers before starting the next section; you should give them 10-15 minutes per section.
- The students in each group should make sure that they all have the same values in the table. The instructor should move around the room to ensure the tables are correct. The conclusions will be off if they are not.
- Note on USDA data: we are using the market value for total agricultural products (includes dairy and meat) not just crop value. We are assuming that some crops, such as hay and alfalfa, are used directly as animal feed.
The students will probably finish half of the worksheet (up to section 3) during the first 60-minute period. If the instructor is using two class lectures for the exercise, ask students to bring worksheets to the following class period. If the exercise is being used during a 2+ hour lecture or during a lab period, then students continue to completion.
Unit 3.2 Activity Completion and Discussion (60 minutes)
During the second class period, students will complete the worksheet and then get back into their groups and discuss their results. Again, the instructor should make sure that they all have the same values in the tables.
- If the number of groups is relatively small (less than 8) then the instructor should have the groups debrief to the rest of the class.
- The instructor can use the
- If the class is large, then the instructor can hand out the answer key and groups can use that to make check their answers.
Teaching Notes and Tips
- The instructor should complete the student exercise prior to teaching it and be familiar with the answer key.
- One of the goals of this unit is to have students be able to extract data from large data tables. Some students may be overwhelmed with the data tables at first and it may be helpful to give students rulers and highlighters to assist in reading the rows and marking the relevant data.
- If time is limited or for any other reason, the number of states examined in the student exercise can be reduced from seven to three that represent East, Midwest, and West (such as Pennsylvania, Nebraska, and California).
The instructor can have students hand in the completed worksheet as a formative assessment that can be graded on a pass/fail basis. The goals in Unit 3 will be assessed in the module-wide summative assessment.
What follows is a rubric instructors can use to evaluate student answers to the worksheet.
Rubric for Unit 3 Assessment (Microsoft Word 2007 (.docx) 18kB Feb25 17)
References and Resources
Maupin, M.A., Kenny, J.F., Hutson, S.S., Lovelace, J.K., Barber, N.L., and Linsey, K.S., (2014). Estimated use of water in the United States in 2010: U.S. Geological Survey Circular 1405, 56 p., Reston, VA: US Geological Survey.
US Department of Agriculture, (2014). 2012 Census of Agriculture.