2012 Annual Report 1a.Objectives (from AD-416): Continue investigation of the manipulation of terrestrial ecosystems which can offset human induced carbon emissions to the atmosphere for the next 40 years by sequestering additional amounts of carbon in soils and vegetation. 1b.Approach (from AD-416): Develop field experimental protocol to evaluate the spatial variability of C storage in soils under different regimes. Develop protocol for chemical fractionation of soil carbon pools that will delineate the effects of climate on carbon storage. Develop predictive interpretation methodology for describing carbon compartmentalization as a function of changing climate. Develop N-15 pool dilution technique to quantify nitrogen pools and processes in soils under different climatic regimes and the effect on C storage. 3.Progress Report: The project contributes to Sub-objective 3a “Determine soil carbon (C) sequestration rates and carbon dioxide (CO2) flux as influenced by agroecosystem drivers (e.g. soil, topography, micro-climate, organisms, management)" of the parent project. Substantial results were realized over the past three years of this project. Soil carbon storage, which influences soil health and climate change, increased by 15 to 20% within three years after a conventional corn rotation was replaced with perennial grass (switchgrass). The switchgrass cultivars Kanlow and Cave in Rock resulted in the highest input of carbon into the soil. Other positive benefits of growing switchgrass included an increase in nitrogen use efficiency. For example, switchgrass used 40 to 55% of the applied fertilizer nitrogen whereas the conventional corn rotation used 30 to 40% of the applied fertilizer nitrogen. Switchgrass can be grown as an alternative crop for biofuel and appears to enhance soil quality and nitrogen use efficiency. Soil carbon storage is dependent upon decomposition of organic substrates and the types of organisms in the soil. We found that the addition of simple or complex carbon substrates to the soil produced a rapid initial burst of carbon dioxide followed by a steady decline over time. This burst and decline in carbon dioxide was related to the substrate composition and sand content of the soil. Substrates that are used readily by soil microorganisms are processed rapidly into more recalcitrant forms of carbon and persist in the environment longer as stored carbon. Sandier soils were found to store more recalcitrant forms of carbon, possibly due to their high aeration and fast initial decomposition. This information is important for managing crop residues to maximize soil carbon storage. The Department of Energy has extended this project for an additional year to compile and report the data from this valuable research.