TEACHING ALL VOLUMES SUBMIT WORK SEARCH TIEE
Volume 6: Table of Contents TEACHING ISSUES AND EXPERIMENTS IN ECOLOGY
ISSUES: FIGURE SETS

Figure Set 4 homepage Carbon Sequestration in Agricultural Soils

Purpose: To teach students that degraded agricultural soils can sequester carbon, and that there are certain management strategies that can maximize carbon storage in soil.
Teaching Approach: Paired Think Aloud
Cognitive Skills: (see Bloom's Taxonomy) - knowledge, interpretation, synthesis
Student Assessment: Short Essay

BACKGROUND

Many agricultural fields in temperate regions have been cultivated for hundreds of years. In these fields, much of the carbon stored in soil has been lost to the atmosphere due to enhanced decomposition during cultivation (See Figure Set 1). Under conventional crop management, soil carbon loss eventually levels out & remains at a steady state at approximately 50% of original carbon levels. However, certain management strategies can slowly increase soil carbon content back towards original levels, which is called soil carbon sequestration. This can occur when net primary productivity due to plant growth exceeds respiration of organic carbon by soil biota. See Schlesinger (1999 - pdf included) or Post and Kwon (2000) for more information about carbon sequestration on agricultural soils. A simple explanation of carbon sequestration can be found at the U.S. EPA website: http://www.epa.gov/sequestration/local_scale.html.

The data on soil carbon sequestration in Figure 4 were collected from a Long Term Ecological Research (LTER) Experiment at the W.K. Kellogg Biological Station in southwest Michigan. In this experiment, six ecosystems were established in 1989 and compared from 1989 to 1999 to characterize their ability to sequester carbon in the soil. These systems were compared to conventionally tilled (physically turned over) agricultural fields in which soil carbon concentrations were hypothesized to remain relatively unchanged over time. The first three ecosystems were cultivated with annual crops, in a corn-soybean-wheat rotation.

The last three agroecosystems contained perennial plants and no tillage.

<top>