Appl Biochem Biotechnol (2011) 165:270–278 271 ~44–78 Gt of C worldwide [2–6]. Causes of this disequilibrium can be traced to unsustainable agricultural practices such as excess tilling, overharvesting of crops, and overreliance on chemical fertilization. The importance of retaining C in soil in the form of stable soil organic carbon (SOC) is also underestimated. One of the best ways to increase the stable SOC is to use C-rich fertilizers that have low turnover after introduction into soil [2, 3]. Better strategies for improving the organic C content of soil involving recycling of organic C could help offset the loss of C from arable lands. But directly amending soils with vegetal matter, especially matter rich in lignocellulose, is inefficient [9]. The solution to this problem is to compost such materials prior to their introduction into soil. Most composting technologies (including forced air, thermophilic and manure-augmented composting) are however time-, space-, and energy-consuming, and they have large greenhouse gas (GHG) footprints, and poor C sequestration efficiency. When using these methods, >50% of the C in the starting feedstock is lost [10–13]. In this study, we analyzed the C cycling efficiency while processing vegetal matter (oak leaves and discarded urban food scrap) using an alternative method called microaerobic composting (MC). We verified the dominance of microbes from the genus Clostridium to the microbial community during MC, and furthermore tracked the turnover of processed materials in soil over a period of several months. Materials and Methods 3,5-Dintrosalicyclic (DNS) acid was obtained from Sigma, and 89% phenol was from Mallinckrodt. MC fermentors (210 L capacity) were obtained from Bokashicycle, LLC. Atmospheric gas chromatography (gc) columns (3′-silica and 6′-13X molecular sieves), used for measuring changes in CO2, O2, and CH4, were obtained from SRI Instruments. Stabilwax-DA and RtQPLOT 30 m × 0.32 mm ID capillary gc columns, for separation of volatile organic acids (VOAs), alcohols, and ketone metabolites, respectively, were obtained from Restek. Standards for VOAs analyses (acetic, propanoic, butyric, isovaleric, valeric, and caproic acid), alcohols, and ketones (ethanol, acetone, acetylacetone, methanol, propanol, butanol, and pentanol) were obtained from Aldrich, Sigma, and J.T. Baker. All other chemicals were reagent grade or better. Polysaccharides were measured in glucose equivalents using the phenol–sulfuric acid (PSA) carbohydrate assay [14–16]. Polysaccharide glycosyl end group DNS reactive aldehyde-reducing activity (also expressed in glucose equivalents) was measured by an adaptation of Miller"s colorimetric assay to microtiter plates [17, 18]. Changes in the fragmentation state of water-insoluble acid-soluble (WIAS) polysaccharides were tracked using the endpoint fragmentation index (EPF index) assay (summarized in Fig. 1) [18], which is a broad indicator of the progression of the hydrolysis of WIAS polysaccharides. Soil amended with MC-treated feedstocks was a Helvetia silt loam. Field site tests were done at a farm outside Portland (New Earth Farm, Hillsboro, OR). Oak leaves were prepared as aqueous slurries and dispensed into 70-ml capacity air tight serum bottles. Each bottle received 10 g of oak leaves blended with 30 ml of 1 g/L glucose solution and 1 ml of wheat bran slurry filtrate. This slurry was prepared by suspending 5 g of wheat bran rich in Clostridium sp. spores in 50-ml water followed by passing the slurry after overnight incubation at room temperature (~21 °C) through a stainless steel sieve (0.5 mm). Leaf slurries were added in equal amounts to each of a series of bottles sufficient in number to allow for triplicate harvests at different time intervals during the experiment.