Nutrient and carbon balance during the composting of deep litter

During the storage of solid animal manure, biological transformation of nitrogen (N) and carbon (C) may increase the temperature from 60 to 70 degrees C, i.e. composting. Composting may cause emission losses of ammonia (NH3) and carbon dioxide (CO2). Furthermore, plant nutrients may leach from the compost heaps. During a composting period of 197 day from September 1997 to April 1998, emission of NH3, nitrous oxide (N2O), methane (CH4) and CO2 was measured using dynamic chambers covering three heaps of deep litter from a house with dairy cows. Leaching of nutrients during composting was determined. Denitrification was estimated as N unaccounted for in an N mass balance. The heaps were either mixed once after 30 days, compressed initially or left untreated. Compacting the heap caused a temperature increase from 10 to 50-60 degrees C. The temperature increased from 30 to 40 degrees C in the heap being mixed. From both the compacted and mixed heap, the cumulative ammonia volatilization was 0.2 kg N/t corresponding to between 2.6 and 3% of the total N. Half of this amount was lost from the untreated heap in which the temperature only increased marginally in the first days after the start of the experiment. Cumulative CO2 losses were 33 (19%), 20 (12%) and 17 kg C/t (10%) from the litter mixed after 30 days, compressed deep litter and untreated deep litter, respectively. Emissions of N2O and CH4 were low. Nitrogen losses due to leaching were < 0.8% of the initial N. Total nitrogen losses due to denitrification, NH3 emission and leaching was from 5 to 19% of the initial N, the lowest from mixed and the highest from untreated litter. (C) 1999 Silsoe Research Institute.