Appl Biochem Biotechnol (2011) 165:270–278 277 toward acidic conditions, and the continuous presence of small amounts of O2 blocks methanogens. MC therefore appears to be a more efficient means of recycling C into soil than AC. Because MC can operate as a close circuit system, it is feasible to control (scavenge, restrict) soluble nitrogen compounds and thus limit the emission of N2O. The progressive falloff in EPF index values after amendment of the composted materials into soil shows that degradation continued, albeit at a slower rate. Based upon our measurements, within 1 year, ~10% of the amended polysaccharides will remain in soil. Amending MC processed food scrap into soil caused the soil to become briefly more acidic, over a period of few days to a little more than a week, after which the pH rose steadily back to the baseline of controls within 5 months. Our results indicate that the turnover of polysaccharides and pH is linked. The relationship between soil polysaccharide content relative to the load of processed food scrap amended back into the soil is complex. An upper threshold of soil polysaccharide content peaking in the range of 6–9% (DW) occurred as MC processed food scrap was added to soil. Variability in the polysaccharide content relative to different load levels was also seen. Some of this variation could be due to a priming effect. This effect assumes that C added back to soil induces the growth of microbial populations, causing a rise in the capacity of soil to fix more C [30]. Based on VOAs, the processing of organic C continued months after addition of MC- treated feedstock to soil. Momma et al. [31] proposed a biological soil disinfestation strategy (i.e., killing certain soil-borne diseases) based on amending organic materials such as wheat bran in soil subsequently flooded with water to induce anaerobic generation of acetic and butyric acid, which they identified as effective suppressants in blocking the growth of Fusarium oxysporoum f.sp. lycopersici and Ralstonia solanacearum. Browning et al. [32] showed that butyric acid amended in sand at a concentration of 0.88 mg g−1 markedly suppressed survival of plant parasitic and fungivorous nematodes. Since the concentration of butyric acid detected in soil amended with MC-processed food scrap 2 months out was 0.8 mg g−1 soil, adding MC-processed vegetal matter to soil warrants further study as a strategy for suppressing the growth of plant pathogens and parasites. Lastly, one potential application of combining MC with soil amending is in the processing of urban food scrap and vegetal debris. Considering mid-range loads amended into soil in this study (~20–40 kg m−2), and assuming a 1-year turnover, we calculate that one hectare of soil has the capacity to assimilate 200–400 metric tons of processed food scrap and/or vegetal debris yearly. A MC facility with a capacity of ~100 m3 and a residence time of materials in fermentors of 2 weeks would require ten hectares of land to process 2,000–4,000 metric tons of food scrap per year. Acknowledgments This work was supported by a grant from the Center for Sustainable Processes and Practices at Portland State University and by a faculty development award from the Office of Research and Sponsored Projects. We also want to acknowledge Scott Olsen from New Earth Farm (Hillsboro, OR). Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. Angulo-Brown, F., Sanchez-Salas, N., Barranco-Jimenez, M. A., & Rosales, M. A. (2009). Renewable Energy, 34, 2344–2352.