Global warming is caused when excessive amounts of carbon dioxide, nitrous oxide, methane and chlorofluorocarbons trap the heat from solar energy in the atmosphere. During the past two centuries, soils have been a net source of greenhouse gases, especially carbon. A recent trend in policy dealing with global warming has been to investigate the possibility of utilizing agricultural practices to aid in lessening the global warming problem, rather than contributing to it. One focus has been to increase soil organic matter, thus using the soil as a sink for carbon. Other benefits of increasing organic matter (sequestered and stored carbon) levels include elevated soil water holding capacity, increased retention of plant nutrients, improved soil...