Shredded straw of Miscanthus was composted in 800-L boxes with different amounts of pig slurry added as nitrogen source. The impact of the different initial C/N ratios (11, 35, 47, 50, and 54) on the composting process and the end product was evaluated by examining chemical and microbiological parameters during 12 months of composting. Low initial C/N ratios caused a fast degradation of fibers during the first three months of composting (hemicellulose: 50-80%, cellulose: 40-60%), while high initial C/N ratios resulted in 10-20% degradation of both hemicellulose and cellulose. These differences were reflected in the microbial biomass and respiration, which initially were higher in low C/N treatments than in high C/N treatments. After 12 months of composting, this situation was reversed. Composts with high initial C/N ratios had high microbial biomass (15-20 mg ATP g-1 OM) and respiration rates (200 mg CO2 h-1 g-1 OM) compared to treatments with low initial C/N ratios (less than 10 mg ATP g-1 OM and 25 mg CO2 h-1 g-1 OM). This could be explained by the microorganisms being nitrogen limited in the high C/N ratio treatments. In the low C/N ratio treatments, without nitrogen limitation, the high activity in the beginning decreased with time because of exhaustion of easily available carbon. Different nitrogen availability was also seen in the nitrification patterns, since nitrate was only measured in significant amounts in the treatments with initial C/N ratios of 11 and 35. The microbial community structure (measured as phospholipid fatty acid, PLFA, profile) was also affected by the initial C/N ratios, with lower fungal/bacterial ratios in the low compared to the high C/N treatments after 12 months of composting. However, in the low C/N treatments higher levels of PLFAs indicative of thermophilic gram-positive bacteria were found compared to the high C/N treatments. This was caused by the initial heating phase being longer in the low than in the high C/N treatments. The different fungal/bacterial ratios could also be explained by the initial heating phase, since a significant correlation between this ratio and heat generated during the initial composting phase was found.
Solid pig manure (240 g kg −" DM) and solid cattle manure (150-180 g kg −" DM) were stored in an open storage facility during spring-summer and autumn conditions for periods of 9-14 weeks during 1994 and 1995. Concentrations of C, N, P and K were determined prior to and after storage, corrected for dry matter losses and distance from the surface. Temperature and, in experiments with pig manure, gas phase composition inside the manure heap were monitored during storage. Nitrogen losses as ammonia volatilization, nitrous oxide emission and leaching were measured, while total denitrification was estimated from mass balance calculations. For both cattle and pig manure there was little difference between seasons with respect to the pattern of decomposition, as reflected in temperature dynamics and C\N turnover. In contrast, there was a distinct difference between manure types. Pig manure was characterized by maximum temperatures of 60-70 mC, although the concentrations of oxygen and methane clearly demonstrated that anaerobic conditions dominated the interior parts of the heap for several weeks. Losses of C and N from pig manure both amounted to c. 50 %. In contrast, the temperature of cattle manure remained close to the air temperature throughout the storage period and cattle manure had lower, not significant losses of C and N. Leaching losses of N constituted 1-4 % with both manure types. Ammonia volatilization from cattle manure constituted 4-5 % of total N, and from pig manure 23-24 %. In pig manure a similar amount of N (23-33 %) could not be accounted for after storage, a loss that was attributed to denitrification. Nitrous oxide emissions amounted to 2 % of estimated denitrification losses.
Concentrations of N 2 0 in gas samples taken from dungheaps of cattle and pig manure were up to 100 times greater than the atmospheric concentration. The concentrations varied little with time but tended to increase with depth. The concentrations were less in fresh manure than in stored manure, and less in cattle manure than in pig manure. The rate of release of N 2 0 from the manure surface was also determined. The mean rate from stored pig manure was 1 1 mg N20-N m-' h-', which is low compared to typical total-N losses. The production of N 2 0 is probably caused by microbial denitrification but could also arise from nitrification. The release of N20 may be accompanied by a greater release of N2, as the conditions in manure favour the denitrification process going to completion.
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