Dr. Rattan Lal
Ohio State University
The greenhouse effect is caused by atmospheric gasses, including carbon dioxide, methane and nitrous oxide, that help trap heat near the earth’s surface and is essential for life. However, burning of fossils fuels has increased the concentration of carbon dioxide (CO2) in the atmosphere and created an increase in the temperature at a rate of more than 0.1 C/decade, an effect known as global warming. Because the potential impact of global warming can affect sea level and climate, scientists are evaluating ways to sequester carbon into pools, such as vegetation and soil, where it can reside for 10 to 35 years. Typical disposition of organic residues results in 60 to 80% of the carbon returning to the atmosphere as CO2. Agricultural practices can reduce these emissions by increasing the density and depth of carbon in the soil profile and decreasing the decomposition of carbon and losses due to erosion. Tillage and planting practices that reduce soil erosion and the land application of manure and other organic materials can increase carbon sequestration. There are also hidden carbon costs associated with fertilizer, pesticides and irrigation due to emissions of CO2 during manufacturing and from energy consumption. Changes in agricultural practices have the potential to reduce carbon emissions by 288 million tons/year in the U.S. and 1 billion tons/yr worldwide. Although it is not a long term solution, soil sequestration of carbon has the potential to help reduce CO2 emissions to a more sustainable level while alternative energy sources are being developed.
Discussion:
Charlotte Bedet (OSU) questioned the Department of Energy slide indicating soil sequestration as a primary means of reducing CO2 emissions. What is the role of the end-use technology which appears to be more dominant after 2050? Lal clarified that soil will play a major role in carbon sequestration only in the next 20-30 years as it is currently the most cost effective option. Carbon emissions are 6 billion tons/year and soil sequestration can only reduce that by 1 billion tons/year. Larger sinks, such as renewable energy alternatives to replace fossil fuels, are needed to have a long term impact. Soil sequestration provides a bridge to that future.
Krishna Vadrevu (OSU), referring to a sustainability index that is determined as a ratio of carbon output to carbon input, asked if net primary productivity is the best measure of carbon output. There is a maximum limit to net primary productivity, thus the harvest index may be a better measure. Lal replied that in order for a system to be sustainable, the index should be 4 to 5 and increasing. That is, the carbon being produced should be 4 to 5 times greater than what is being consumed. The ratio is important not the exact output. The harvest index is limited because it does not consider root biomass.
Notes by Mary Wicks
The OCAMM (Ohio Composting and Manure Management) Program is funded by OARDC/OSU.