Soil, Plants, and the Energy Cycle

Soil Science Society of America

Activity Source: 

Soil Science Society of America. Adapted with permission.

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, as in cotton, flax-linen, and hemp. And they provide shelter materials like wood and brick. But did you realize that soils also are an important part of the energy cycle? Soils sequester carbon dioxide (CO2) 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.

CO2 sequestration is the removal of CO2 from the atmosphere into plants as biomass and soils as organic and inorganic carbon. Sequestration can be maximized by land management practices (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 fuel formulation.

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

Similar to lawns, there are fields of corn, wheat and pasture that have large spots (acres) where biomass is thick and other large spots (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).

Materials

  • Computer with Internet access
  • Printer, paper
  • Pen or pencil

Procedure

Find detailed instructions and the Land Bio-fuel spreadsheet needed to do calculations at www.soils.org/lessons.

Do the activity. As bio-fuel is one of the options we have for fuel, determine how much bio-fuel can be produced by different plants.

Discuss: What kind and how much bio-mass can be produced in an area around your city or town? How many gallons of fuel can be expected from one acre of crop land? How much carbon can be sequestered in the local area?