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Carbon and nitrogen pools and development of alkali extractable organic matter over time, in hog manure solids composted in-vessel Smith, Susan Lois


In three separate experiments, separated hog manure solids and hemlock sawdust were composted in-vessel for a period of 46 to 55 days. The effects of temperature and aeration on monitored carbon and nitrogen pools were examined. Composting temperatures were monitored throughout and samples were taken periodically in order to study carbon and nitrogen pools in humus fractions (humic acid (HA) and fractions of fulvic acid (FA)); in overall compost fractions (polysaccharides, total carbon and nitrogen); and in the water-soluble phase (water-soluble carbon). This was done in order to examine how these nutrient pools were affected by the frequency of aeration; and to obtain information on the processes involved in the development of the alkaline extract over time. For experiments 1 and 2, a bucket-scale apparatus was used for composting. In experiment 3 smaller scale apparatus and controlled temperature waterbaths were employed. For experiments 1 and 2, the effects of aeration were examined on hog manure solids composted with hemlock sawdust for 51 to 55 days in 90 litre buckets. Aeration was carried out by mixing the compost with a metal auger attached to a hand-held drill. The aeration treatments varied in intensity from once every 14 days to once every 2 to 3 days. In the third experiment, composting of separated hog manure solids and hemlock sawdust was carried out using smaller 2 litre vessels submerged in controlled temperature waterbaths, with mixing occurring by shaking manually every other day throughout. Over a period of 46 days, the effects of high and low temperatures on carbon and nitrogen pools and the development of the alkaline extract were examined. Significant increases in utilization of FA carbon (CF), carbohydrate-rich FA carbon (Ca) and the ratio of carbon to nitrogen in carbohydrate-rich FA carbon (C/Nca) were noted under aeration treatment 'A3'. This was the only aeration treatment in the bucket-scale composting to impact the metabolically accelerated thermophilic phase, increasing the oxygen content and optimizing the environment for FA carbon degraders. Overall, in terms of C/N ratios, the most consistent trends were found in the carbohydrate-rich component of FA (FAca). With the exception of experiment 3-' low temperature' compost, C/Nc3 values decreased over time as a result of decreasing Ca. Due to design flaws in the bench-scale waterbath compost system, it was not possible to control moisture loss, making it difficult to definitely attribute chemical changes to the influence of controlled temperatures. Regardless of temperature, utilization of total polysaccharides was substantially lower in bench-scale controlled temperature waterbath composting. This suggests that the activity of organisms which degrade complex carbohydrates may be negatively influenced by the homogeneous environment characteristic of controlled temperature composting.

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