Denitrification from a swine lagoon overland flow treatment system at a pasture-riparian zone interface

In manure disposal systems, denitrification is a major pathway for N loss a nd to reduce N transport to surface and ground water. We measured denitrifi cation and the changes in soil N pools in a liquid manure disposal system a t the interface of a pasture and a riparian forest. Liquid swine manure was applied weekly at two rates (approximately 800 and 1600 kg N ha(-1) yr(-1) ) to triplicate plots of overland now treatment systems with three differen t vegetation treatments. Denitrification (acetylene block technique on inta ct cores) and soil N pools were determined bimonthly for 3 yr. The higher r ate of manure application had higher denitrification rates and higher sail nitrate. Depth 1 soil (0-6 cm) had higher denitrification, nitrate, and amm onium than depth 2 soil (6-12 cm). The vegetation treatment consisting of 2 0 m of grass and 10 m of forest had lower denitrification. Denitrification did not vary significantly with position in the plot (7, 14, 21, and 28 m d ownslope), but nitrate decreased in the downslope direction while ammonium increased downslope. Denitrification ranged from 4 to 12% of total from N a pplied in the manure. Denitrification rates were similar to those from a ne arby dairy manure irrigation site, but were generally a lower percent of N applied, especially at the high swine effluent rate. Denitrification rates for these soils range from 40 to 200 kg N ha(-1) yr(-1) for the top 12 cm o f soil treated with typical liquid manure that is high in ammonium and low in nitrate.