Hands-on Activity: Biochar: Measuring and Improving Soil Function

Contributed by: Nanotechnology RET, Department of Earth Science, School Science and Technology, Rice University

Standing water in clay; standing water in clay with biochar.
A demonstration of standing water in clay (left) versus standing water in clay with a biochar soil amendment (right).
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

Summary

Students learn how to manipulate the behavior of water by using biochar, a soil amendment used to improve soil functions. As a fluid, water interacts with soil in a variety of ways. It may drain though a soil’s non-solid states, or its “pores”; lay above the soil; or move across cell membranes via osmosis. In this experiment, students solve the specific problem of standing water by researching, designing, and engineering solutions that will allow water to drain faster. This activity is designed for students to explore how biochar allows soils to act as “sponges” in order to retain more water.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Measurement is a fundamental concept in science and engineering. Without the ability to measure, engineers would not be able to design and build their experiments, much less iterate upon them. Not only is measurement critical in engineering, it is also important in industries where engineering is essential such as farming, construction, and manufacturing.

In agriculture, measurements of water tend to dictate the amount of produce (such as fruits and vegetables) a piece of land can yield. Agricultural engineers and farmers design and improve upon systems to save water. In one particular instance, agricultural engineers add materials, sometimes known as amendments, to soil in order to aid in water retention. As a result, plants thrive in soils with higher concentrations of water, and avoid wilting or drying out. In this activity, students facilitate engineering designs and work with measurements, water, and soil to come up with designs for water retention.

Pre-Req Knowledge

A basic understanding of science tools with some knowledge of the effects of standing water.

Learning Objectives

After this activity, students should be able to:

  • Describe what allows or prevents fluid (usually water) to move through pore spaces or fractures of different soil types. 
  • Describe how biochar can be used to facilitate hydraulic conductivity. 
  • Evaluate the strengths and weaknesses of different designs for testing hydraulic conductivity.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Plan an investigation individually and collaboratively, and in the design: identify independent and dependent variables and controls, what tools are needed to do the gathering, how measurements will be recorded, and how many data are needed to support a claim. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Students will develop an understanding of the attributes of design. (Grades K - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Students will develop an understanding of the role of society in the development and use of technology. (Grades K - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Students will develop an understanding of the characteristics and scope of technology. (Grades K - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Humans can devise technologies to conserve water, soil, and energy through such techniques as reusing, reducing, and recycling. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • demonstrate the use of course apparatuses, equipment, techniques, and procedures, including meter sticks, rulers, pipettes, graduated cylinders, triple beam balances, timing devices, pH meters or probes, thermometers, calculators, computers, Internet access, turbidity testing devices, hand magnifiers, work and disposable gloves, compasses, first aid kits, binoculars, field guides, water quality test kits or probes, soil test kits or probes, 100-foot appraiser's tapes, tarps, shovels, trowels, screens, buckets, and rock and mineral samples; (Grades 11 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Creativity and innovation. The student demonstrates creative thinking, constructs knowledge, and develops innovative products and processes using technology. The student is expected to: (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Each group needs:

  • 50 mL (or higher) graduated cylinder
  • laboratory-grade metal ware set—suggested dimensions: support stand (8" x 5"), rod (24" height, 12mm diameter), cork lined burette clasp with metal retort ring (2.5" diameter) available at Amazon
  • 100 g of soils (one of each type: clay, sand, silt and loam) available at Wards’s Science
    • Note: loam is a mix of clay, silt, and sand
  • 6 g biochar, available at Amazon
  • 91 cm (½ yard) of organza or similar type fabric (for example, silky fabric used in curtains, dryer sheets) available at Amazon 
  • stopwatch
  • 4 rubber bands
  • 200 mL graduated cylinder, for measuring water
  • 4 – 5 funnels (optional), available at Amazon
  • mortar and pestle (optional), available at Amazon
  • Access to a computer with PowerPoint® to view the Measurements with Biochar Presentation, or a printout of the presentation
  • Lab Presentation Rubric

For the class to share:

  • scale— scientific scale or a simple kitchen scale able to measure 2 g to 50 g
  • plastic graduated cylinders or plastic 2-liter soda bottles; students can cut and/or redesign a soda bottle to imitate the functions of a graduated cylinder; for example, turning a 2-liter bottle upside down and using the bottle top as the draining point 
  • funnels for pouring soil types into the graduated cylinders
  • scissors, for cutting the plastic graduated cylinders or soda bottles
  • masking tape and markers, for labeling graduated cylinders 

Introduction/Motivation

In terms of water, what is the cost of producing the items listed in Table 1 below? 

[Student responses will and should vary. The idea is for students to pause and reflect on the vast amount of water needed to produce just one item (for example, an apple). Use Table 1 for answers to how many liters of water are needed per kg of the item.] 

A table that lists various food products with the amount of liters of water needed per item.
Table 1. Products and the amount of water needed to produce each item.
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

Over the course of this activity we will explore how to manipulate the behavior of one of the most important molecules on this planet: water. We will study why it is important to be able to manipulate water (H2O) and how a soil amendment, biochar, can aid in drought prevention and prevent standing water. We will use various lab equipment and apparatus to carry out the experiment with precision and safety. 

There are two weather- and climate-related phenomena that engineers must contend with when considering situations that involve water: an overabundance of water that may lead to flooding, and a lack of water that may lead to drought. Both flooding and drought are what agricultural engineers strive to mitigate, particularly now in the face of climate change and the severe weather that occurs because of it.

Flood waters have both visible and hidden dangers. Visible dangers are usually obvious: erosion of land and destruction of property and infrastructure that distribute swaths of debris to large areas. Hidden dangers are microscope in nature: bacteria, viruses, and germs that begin to feed and multiply in the standing water as a result of flooded sewer lines.  Previous flood waters, such as those in the aftermath of Hurricane Harvey in 2017, contained flesh eating bacteria, which eventually caused the death of two volunteers. Standing water also serves as a perfect breeding ground for mosquitoes and mosquito-borne illnesses. Studies have shown an increase in West Nile virus in Gulf Coast areas affected by Hurricane Katrina in 2005.

Devastation caused by floods, of course, comes to mind when water is mentioned as a weather phenomenon, whereas droughts can be overlooked unless you ask farmers and agricultural engineers. Droughts are more of a long-term, climatic effect that can occur over the course of several months or years. Drought in California from 2012 to 2017 was one of the driest on record and impacted groundwater and reservoir storage as well as forests—millions of trees died because of a lack of water. Droughts also disrupt agriculture, causing damage to croplands. In extreme but rare cases, droughts can cause famine due to crop loss.

[For an engineering scenario, present the real-world after effects of Hurricane Harvey in 2017 to students. Have the students propose a solution to preventing standing water before the next hurricane season. Likewise, have another set of students propose a solution to city planners for easing the after effects of a severe drought in California. After modeling and completing this experiment, students should be able to propose various solutions. Students may propose adding biochar in both scenarios. In Houston, biochar could be added to soils city-wide, allowing for standing water to be drained and absorbed at a faster rate. In California, addition of biochar in drought-prone areas would ease the severe impacts caused by lack of water. If biochar is applied to soils before the drought, the soils would have higher water retention levels and ease the economic impacts caused by droughts.]   

Vocabulary/Definitions

amendment: A product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics.

biochar: A solid carbon-rich material obtained from burning biomass in the absence of oxygen, which prevents combustion and instead produces a mixture of solids similar in physical form to ashes or charcoal.

biomass: In energy production, any organic matter such as plant or animal matter than can be used for fuel.

flow rate: Quantity of liquid moving through the soil expressed cubic meters per second, or in cubic feet per second or gallons per minute.

hydraulic conductivity: The ease with which a fluid, usually water, can move through pore spaces or fractures in soil.

soil: A mixture of organic matter, minerals, gases, liquids, and microorganisms that form the outermost layer of the Earth; also a means of water storage, supply, and purification.

Procedure

Background

Soil water holding capacity and hydraulic conductivity (K) are two important properties of soil. Soil water holding capacity is the amount of water different types of soil can hold. Hydraulic conductivity is the ease with which water can move through the pores or fractures of the soil.  Over the next few class periods, students explore how biochar added to four different soil types affects the flow rate of water. 

This activity demonstrates measuring procedures and techniques within the context of soil science and engineering. It also introduces the use of several course apparatus and equipment including graduated cylinders, scales and balances, timing devices, calculators, and computers with internet access.

Before the Activity

  • Stress the importance of precise measurement, along with the importance of using the metric system. 
  • Make copies of the Lab Presentation Rubric.
  • If needed, printout and make copies of the Measurement with Biochar Presentation.

With the Students

Day 1:  Stage all the materials.  Students should conduct this activity with teacher supervision.     

  1. Lead students through the Introduction/Motivation section, and conduct the Pre-Activity Assessment.
  2. Tell students to select two soil types: sand and clay.
  3. Have students measure 50 grams of each soil type.
  4. Instruct students to hollow out the bottom of four plastic graduated cylinders.
    • Either cut the entire bottom using a pair of scissors or poke several holes on the bottom using a push-pin.
  1. Cover the hollowed-out bottom with either organza fabric, mesh cloth or a simple dryer sheet.  Affix the organza fabric, mesh cloth, or the dryer sheet with a rubber band, as in Figure 1.

Photo on the left shows graduated cylinders with base, organza fabric, and a rubber band. Photo in the center is a close-up of a 100 mL graduated cylinder with the bottom cut out. Photo on the right shows a mock-up design with organdy fabric covering the bottom of a graduated cylinder cover with organdy fabric, which is held in place by a rubber band.
Figure 1. Two graduated cylinders, organza fabric, rubber band, and a stand (left); cylinder with the bottom cut out (center); the finished testing product (right).
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

  1. Have students mark and fill two graduated cylinders with soils only, using the pre-measured soils (50 g sand, and 50 g clay).
  2. Have students mark and fill the other two graduated cylinders with soils + biochar and mix them into a homogeneous mixture. The soil + biochar measurement for each cylinder should be:
    • 48 g sand + 2 g biochar
    • 48 g clay + 2 g biochar
  1. Have students begin the hydraulic conductivity test. Instruct students to place the hollowed-out cylinders into larger graduate cylinders partly-filled with water, as in Figure 2. Let the samples sit until sully saturated, then have students raise the samples so that the soils can drain. Drain the soils until no standing water remains; this may take up to 24 hours so leave the samples overnight.

Left photo shows soil being saturated in water. Photo on the right shows water draining through the soils.
Figure 2. Soil samples being saturated in water (left); water draining through soil samples into cylinders (right).
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

Day 2:  Allow students to use the attached Measurements with Biochar PowerPoint Presentation for a model to follow.  If time permits, then allow students to design and/or reengineer the model.   

  1. Remind students that they are acting as agricultural engineers, exploring the effects of biochar to devise solutions for mitigating the effects of floods and draughts.
  2. If not already in place, have students place the plastic graduated cylinder on the support stand, as in Figure 3, and the other graduated cylinder below to catch draining water. Remind students that the hydraulic conductivity is the ease with which water can move through the pores of the soil, so they will be measuring the time it takes the water to move through the soils. Distribute a stopwatch to each group.
  3. Tell students to fill the sample-containing plastic graduated cylinders with 200 mL of water.
  4. Have students measure the flow rate, the amount of water that drips through the soil, by measuring the time to takes a given amount of water (around 100-150 mL works well) to flow through the soil. Make sure each group records their results, as they will graph them later.
    • Note: water will flow through sand in one 60-minute period, but silt could take upwards of 90 minutes, and clay will take 3-4 days.
    • While the water is draining, have students brainstorm different design solutions for testing hydraulic conductivity. Remind students that they will present their solutions to the class, as in the Activity Embedded Assessment.
    • Have students begin preparing their presentations. Distribute the Lab Presentation Rubric. Have students write down their hypothesis and experimental design, and brainstorm ways to communicate their data (via graphs and tables).

Photo on the left shows a support stand with base and a cork lined burette clamp.  Photo in the center shows the same support stand with base and a cork lined burette clamp holding a 50 mL plastic graduated cylinder.  Photo on the right shows the same support stand with base and a cork lined burette clamp holding a 50 mL plastic graduated cylinder.  The graduated cylinder is covered with organza fabric, which is held in place by a rubber band.
Figure 3. A mock-up of the support stand (left); holding a graduated cylinder with the bottom cut out (center); the finished testing product (right).
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

Day 3-4:  Continue to test hydraulic conductivity. 

  1. The sand hydraulic conductivity test should be completed. Have students clean out the sand cylinders and repeat the experiment with loam. Water may continue flowing through the clay while students conduct the loam experiment.
  2. Have students present their solutions for testing hydraulic conductivity, ask them questions from the Activity Embedded Assessment.
  3. As time allows, ask students groups to brainstorm answers to the Investigating Questions. Lead a class discussion about the effects of biochar, and how engineers can utilize biochar to aid in flood- and draught-prone areas.

Day 5:  Students should present their data, inferences, and conclusions.

  1. Recommend students present data using graphs, reference the Measurements with Biochar Presentation and Figure 4 as an example. 
  2. If computers are available, allow students to use PowerPoint to present their findings.
  3. Use the Lab Presentation Rubric for constructive feedback, and grades.  

Images show sample bar graphs presenting the flow rate of water in soils type.
Figure 4. Sample bar graphs presenting the flow rate of water in soils type.
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

Top left photo shows a high school student measuring hydraulic flow rate.  Top right photo shows three high school students measuring biochar on a triple beam balance.  Bottom left photo shows three high school students observing hydraulic flow rate.  Bottom right photo shows three high school students presenting their findings.
High school students conducting the measurements with biochar experiment. Students are at different stages of the experiment from measuring to presenting their findings.
copyright
Copyright © 2017 Chetan Sawhney, RET Program, Department of Earth, Environmental, and Planetary Sciences, Rice University.

Attachments

Safety Issues

  • Use gloves for biochar as it may leave a black residue, which is washable with soap and water. 

Investigating Questions

  1. What effect does biochar have on the hydraulic conductivity of the three soils?

Sample answer: Biochar acts a sponge.  This allows for faster draining and longer absorption of water when biochar is present in soils.  

  1. How could biochar be engineered for use in flood or standing water prevention?

Sample answer: If biochar is added to soils, it would allow standing water to drain faster (hydraulic conductivity), while holding water for longer periods of time.  If biochar is not added to soils, there would be no impact to water conductivity and evaporation rates. 

  1. How could biochar be engineered for agriculture and in aiding the growth of plants? 

Adding biochar to soils could increase plant-available water rates.  Meaning that the roots of plants would have longer times to absorb water and access to additional water in soil that was not present before adding biochar.  This is possible due to the higher porosity (holes) levels of biochar.  Scientifically, water holding capacity in soil would increase and hydraulic conductivity times would decrease. 

Assessment

Pre-Activity Assessment

Brainstorm: Aimed at building brainstorming skills, ask the students:

  1. Why is it important for water to make it through the pores of the soil? 

Water needs to travel through the pores of soil to prevent standing water and floods.  Increased plant available water, sustainment of a steady water table, and refilling aquifer levels are other reasons why water needs to travel through the pores of soil.

  1. What are some ways we can test the flow rate of water in different soil types?

One way to test flow rate is to gather some soil from the subject area and place it in a cylinder or funnel and then pour water through the collected soil.  Answers will vary.    

Activity Embedded Assessment

Design Presentations: After each group creates one or two design solutions for testing hydraulic conductivity, have them present their best design and answer the following questions:

  1. Did your design allow for specific and exact measurements, how can it be verified? 

The soil can be measured using a triple-beam balance and water can be measured.

  1. What are advantages and disadvantages of the engineered design?  

Student responses will vary based on their design.  An advantage could be cost, where simple lab materials can be used to test flow rate.  A disadvantage could be the design did not allow for any water to travel through the pores.  It confined the water to remaining on top of the soil’s surface. 

Post-Activity Assessment

Final Presentations and Project Reflections: After testing their design, have students consider again the questions from the activity-embedded assessment, as well as the following. 

  1. Evaluate the presentation using the Lab Presentation Rubric assigned. Use the rubric to also allow students to self-grade their lab and presentations. 
  2. Did students present measurement data in chart format, bar, column, pie, scatter plot, etc.? 
  3. Does the design allow for reproducibility, meaning multiple trials? 

If the design allowed for at least three (3) trials with similar data, then the design was a success.  If not, reengineering and modification may be needed.   

Activity Extensions

Have students research other environmental areas where biochar can aid in mitigating the effects of climate change.

Activity Scaling

  • For lower grades, allow students to explore water retention levels and identify different types of soil.  Students can explore different types of soil by digging about six inches into the ground, using school or campus grounds will allow instant connections to their learning environment.  Then, have the students mix that soil with a little water.  If their soil can be formed into a shape, like a sphere ball, then clay is the type of soil.  If their soil loses shape or does not form a shape, then sand is the type of soil.  If their soil can be formed into a shape, like a sphere ball, but then crumbles easily upon squeezing, silt is their type of soil.    
  • For lower grades, have an adult hollow out the bottom of the graduated cylinders.
  • For higher grades, have students research other possible feedstock for biochar and how else biochar can aid in mitigating global climate change.  
  • For higher grades, have students list the different variables (independent, dependent, and control).  Provide access to PowerPoint for developing for graphing of data. 

References

Brady, Nyle and Weil, Ray. The Nature and Properties of Soils. Prentice Hall, 2001.

Brewer, Catherine E., et al. “New approaches to measuring biochar density and porosity,” Biomass and Bioenergy. 66: 176-185. 2014. https://doi.org/10.1016/j.biombioe.2014.03.059

Interactive Tools – Product Gallery. 2017 Water Footprint Network. Accessed September 11, 2018. http://waterfootprint.org/en/resources/interactive-tools/product-gallery/

Liu, Zuolin; Dugan, Brandon; Masiello, Caroline; and Gonnerman, Helge. “Biochar particle size, shape, and porosity act together to influence soil water properties.” PLoS ONE 12: e0179079. 2017. https://doi.org/10.1371/journal.pone.0179070.

2000m^2: The Global Field. 2016. Agricultural and Rural Convention * ARC2020. Accessed September 11, 2018. https://www.2000m2.eu

Contributors

Chetan Sawhney

Copyright

© 2018 by Regents of the University of Colorado; original © 2017 Rice University

Supporting Program

Nanotechnology RET, Department of Earth Science, School Science and Technology, Rice University

Acknowledgements

This material was developed in collaboration with the Rice University Office of STEM Engagement, based upon work supported by the National Science Foundation under grant no. EEC 1406885—the Nanotechnology Research Experience for Teachers at the Rice University School Science and Technology in Houston, TX. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or Rice University.

Special thanks to Dr. Xiaodong Gao, and Dr. Caroline Masiello for their dedication, time, and tutelage; Dr. Carolyn Nichol, Christina Crawford, and Isaias Cerda of the R-STEM program at Rice University for the opportunity. 

Last modified: September 17, 2018

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