Oak Ridge National Laboratory
Mentor: Mac Post
Analysis of factors influencing soil response to no-till agriculture.
U.S. emissions currently constitute about 20% of the world’s fossil CO2 output (U.S. emissions in 1996 were about 1.45 Gt-CDIAC, 1999). Approximately one-fifth of the U.S. land area is used for agriculture (FAO, 1995), thus making agriculture an important resource in managing terrestrial ecosystems for mitigating fossil CO2 emissions. The common method of moldboard-plowing the soil before planting leads to erosion, enhanced decomposition of organic carbon, and the consequent emission of carbon dioxide from soil (in addition to fossil emissions). Changing from conventional-till to conservation-till could retain or sequester large amounts of carbon. Lal (1998) estimates the overall potential of U.S. cropland for carbon sequestration in soil as 0.075 to 0.208 Gt C/year. This could offset 5.1%-14.3% of the U.S. fossil emissions. However, the effect of a change in tillage on carbon sequestration depends on the soil type, initial carbon content, climate, and cropping history of the area. The purpose of my research was to examine the relative importance of these factors. In general, I found that areas with the greatest potential have moderate temperature and precipitation and have mesic-typic soils with high clay content. Most experiments show that cropland that was tilled intensively for a long time prior to conservation tillage is slowest to rebound to a higher SOC content. A significant difference in surface soils (0 to 7.5 cm) versus deep soils (7.5 to 15 cm) was observed. Surface soils exhibited an increase in SOC after transition to no-till whereas deep soils often, but not always, showed a slight decrease. As an example, in similar sites the surface layer in a conventional-tilled plot was found to have 2.81 kg SOC/m2 whereas the corresponding no-till plot had 3.71 kg SOC/m2. At the same site, deep soil under conventional-till had 3.26 kg SOC/m2 and 3.01 kg SOC/m2 under no-till.
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