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Biofuel: Classroom Activities

Soil, Plants, and the Energy Cycle


To better understand the connection between soil type and biomass yield.

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Background Information

Soils are critical for many aspects of our daily life. They provide food such as grains, vegetables, and animal feed. They provide fiber for clothing, such as cotton, flax-linen, and hemp. They also provide building materials, such as wood and clay for making bricks. Soils are also an important part of the energy cycle. They contain carbon dioxide (CO2) which they get from energy used by plants. Plant materials — such as residues, oils, and grains — grown from soil can be used to produce ethanol or biodiesel for energy.

Carbon dioxide is an important gas in the Earth's atmosphere. It is one of the primary gases responsible for absorbing and emitting radiation. This process is the cause of the greenhouse effect, which is responsible for the warm temperatures in Earth's lower atmosphere. The sequestration of CO2 is the removal of CO2 from the atmosphere into plants as biomass and soils as organic and inorganic carbon. One way that sequestration can be maximized is by using certain agricultural methods, known as best management practices, or BMPs. There are BMPs that increase sequestration rate, increase carbon storage capacity, and minimize carbon loss from soil disturbance. Successful BMPs include grassland restoration, wetland restoration, and conservation tillage. Conservation tillage lets cropland become a net carbon sink (the rate at which carbon is stored is higher than the rate at which it is released) with improved water and nutrient use. Soil tillage breaks down soil organic carbon (SOC), exposing it to oxygen and releasing stored SOC back to the atmosphere as CO2.

Perennials, high-residue crops, and legumes sequester carbon. Perennial grasses and perennial forage legumes can be harvested multiple times and re-grow without being replanted. The root system acts as a large carbon sink. Annual high-residue crops like corn and wheat also sequester carbon, as do grazing lands.

Plant materials can also be used to produce bio-fuel. Land needed to supply fuel depends on the soils and the type of fuel to be produced.

Soil differences can be observed by recording the amount of plant biomass growing in a particular area. If you walk across your lawn, are there places where the grass is thick and other spots where it is thin and you can see bare soil.

Similar to lawns, fields of corn, wheat and pasture can have some large areas (acres) where vegetation is thick and other large areas (acres) where it is thin. The difference is usually due to differences in soil fertility (the relative ability of a soil to supply the nutrients essential to plant growth).

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Activity Overview

Students examine a USDA soil map of their local community. They consider the extent to which the soil could support the growth of a feedstock for producing ethanol .

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Materials and Equipment

Computer with Internet access, printer, paper, pen or pencil

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  1. Instruct students to go to the following website.
  2. Have students open the spreadsheet "Supplementary Worksheet (Excel)" under the "2010 - Exploring Energy" heading.
  3. Have students complete the "Land for Bio-Fuel synthesis" exercise provided on the spreadsheet.
  4. Discuss with your students the following:
    1. What kind and how much vegetation can be produced in the area surrounding your town, city, or community?
    2. How many gallons (or liters) of biofuel can be expected from one acre of crop land?
    3. How much carbon can be sequestered in your local area?

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