Nutrient Losses from Unlined Bedded Swine Hoop Structures and an Associated Windrow Composting Site

Abstract

Mass balance analysis of livestock manure management systems can offer important insight into the flows and losses of nutrients and potential pollutants. This study describes the objectives, design, and two years of results from a field study examining the nutrient losses from bedded swine structures and an associated composting site. Nutrient mass balances have been completed on three groups of pigs in naturally ventilated hoop structures, along with the corresponding three composting trials at the outdoor windrow composting site. Soil core nutrient analysis and mass balances on nutrients in the swine production system and composting piles have been used to assess losses to the environment. The mass balance analysis of deep bedded hoop structures identified significant N losses from the bedded pack (54 ± 6% of the excreted manure; 3.9 kg/pig) but negligible P losses in the hoop. Both N and P losses at the compost site were significant (19 ± 10% and 21 ± 21% of the excreted manure respectively). After losses in both the hoop and the composting process, the nutrient quantities remaining were 1.9 ± 0.4 kg N/pig and 1.0 ± 0.3 kg P/pig. 10% or less of the N losses from the hoop accumulated in the top 1.2 m of soil, and that net accumulation was entirely in the first year. Most N losses within the hoop structure appear to be in gaseous forms, e.g. N2, N2O, and NH3. Improved management of these gaseous losses in bedded livestock systems will be important to making these systems environmentally sustainable. Although soil sample variability precluded a direct correlation between nitrogen losses and soil accumulation at the composting site, high apparent soil accumulations did indicate that a considerable fraction of the N losses observed at the composting site are being leaching into the soil. Design and management strategies to mitigate this leaching loss are likely to be necessary for manure composting facilities in humid regions located near vulnerable groundwater resources.