Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2001
Publication Date: July 1, 2001
Citation: LOWRANCE, R.R., HUBBARD, R.K. DENITRIFICATION FROM A SWINE LAGOON OVERLAND FLOW TREATMENT SYSTEM AT A PASTURE/RIPARIAN ZONE INTERFACE IN THE SOUTHEASTERN COASTAL PLAIN. JOURNAL OF ENVIRONMENTAL QUALITY. 30:617-624(Refereed Co-author #16). 2001. Interpretive Summary: Animal manure stored in lagoons can create environmental quality problems due to either leakage or catastrophic failure of the lagoons. The best way to manage lagoons is to use the liquid manure for crop production, thus recycling the nutrients and organic matter in the manure back to the soil. Nitrogen (N) is a critical element for crop growth, but can also contribute eto water quality problems. When applied as manure, a large amount of N ma be lost by denitrification, the reduction (by bacteria) of nitrate-N in soil to N gas that diffuses into the air. We quantified the amount of denitrification that occurred with two rates of N application swine lagoon manure in an overland flow treatment system at the edge of a riparian (streamside) buffer. The liquid manure was applied to the ground surface through gated pipes at about 800 and 1600 lbs/acre/yr. Denitrification rates and the amount of N in soil was higher for the higher manure application rate. Although denitrification was a significant loss of N from the application area, ranging from 4 to 12% of the total N applied, long-term buildup of N may lead to water quality problems. About 200 lbs/ acre/yr is the maximum denitrification loss that can be expected from a liquid manure land application system. Nitrogen that is lost via denitrification is not available to produce water quality problems.
Technical Abstract: Denitrification is an important sink for N in liquid manure. We examined gaseous N loss by denitrification and the changes in soil N pools in a liquid manure disposal system at the interface of a pasture and a riparian forest. Liquid swine manure was applied at two rates (800 and 1600 kg N ha**-1yr**-1) to triplicate plots of overland flow treatment systems with three different vegetation treatments. The manure was applied from gated pipes on the upslope end of 30m plots and allowed to run downhill toward the bottom of the plot. Denitrification and soil N pools were determined bi-monthly for three years after beginning liquid manure application. The higher rate of manure application had higher rates of denitrification and higher soil nitrate. Depth 1 soil (0-6 cm) had higher denitrification, nitrate and ammonium than depth 2 soil (6-12 cm). Denitrification did not vary significantly with position in the plot (7, 14, 21 and 28 m downslope) )but nitrate decreased in the downslope direction while ammonium increased downslope. Denitrification ranged from 4% to 12% of total N applied in the manure. Denitrification rates were similar to those from a nearby dairy manure irrigation site, but were generally a lower percent of N applied, especially at the high rate. These studies indicated that denitrification rates for these soils might reach a maximum of 200 kg N ha**-1yr**-1 for the top 12 cm treated with liquid manure high in ammonium and low in nitrate.