Nitrogen mass balance for spray fields fertilized with liquid swine waste

The swine industry has expanded rapidly in North Carolina over the last two decades. Animals are raised in confined facilities where waste is flushed into open-air lagoons and the liquid phase is land-applied to receiving fields as an organic fertilizer. The post-application fate has not been fully documented. Therefore, on three occasions I experimentally applied liquid swine waste at typical doses (40 to 130 kg N ha-2) to defined plots in an active spray field on a representative North Carolina swine production facility and constructed an N mass balance for a 14 to 18 d period. Most of the N (52%) was assimilated into plants, while surprisingly little (9%) was volatilized. Microbial immobilization accounted for 10% of the applied N, while 12% migrated below the active soil zone (surface 20 cm) and was presumably lost to groundwater. The soil storage term averaged 16%, while the denitrification sink was inconsequential (<1%).