Over the past 15-years, swine-producing
confined animal feeding operations (CAFOs) have
proliferated throughout the Southeastern United
States, particularly in North Carolina. Waste at these
facilities is collected in open-air lagoons and the
liquid phase is land-applied as fertilizer by sprinkler
irrigation. Numerous investigations have focused on
individual aspects of the fate of nitrogenous liquid
waste, but none has attempted a comprehensive
analysis of post-application transformations and
losses. On three occasions, we experimentally applied
liquid swine waste at typical industry doses of 1.2 and
2.5 cm-ha (40–130 kg N ha 1) to carefully defined
plots in an active spray field on a representative North
Carolina CAFO and constructed a nitrogen mass
balance for the waste by assessing most N pools and
transformations in post-application observation
periods of 14–19 days. We consistently recovered
more N than applied, by an average of 126%. This
was likely due to mineralization of endogenous
organic-N, a reservoir that was not measured. Plant
assimilation clearly represented the most important N
sink for this fertilizer type, accounting for 25–117%
of the applied N. Offsite loss to leaching and
volatilization and onsite accumulation in the inorganic
phase and in microbial biomass all assumed
secondary and roughly equal importance; each term
represented about 5–20% of the applied N. Denitrification
was inconsequential in N loss from a mass
standpoint, accounting for 2% of the effluent. The
post-application fate of N in liquid swine waste did
not differ fundamentally from other organic and
inorganic fertilizers, as the relative importance of all
loss and storage terms fell within the ranges of values
given for other fertilizers. However, liquid swine
waste did differ from other N fertilizers in the rate of
processing. Transformations occurred rapidly due to
the immediate post-application contact of liquid
swine waste-N with plant roots and microbes in a
form (NH4
+–N) immediately available for use.