Nitrogen Leaching from Unlined Cull-Onion Landfills
- J. J. Hutchings,
- J. E. Hammel * and
- J. L. Osiensky
Disposal of cull onions (Allium cepa L.) in unlined landfills in the Treasure Valley region of eastern Oregon and southwestern Idaho is a historic management practice that has been identified as potentially causing NO3-N contamination of regional groundwater. To investigate NO3-N generation and transport during a 6-yr period, monitoring wells were placed in the cull onion waste inside two landfills. The soil below each landfill was instrumented with soil-solution samplers and matric-potential sensors. Four to 6 Mg of organic N were loaded into each landfill in the form of onion waste. Little leaching of NO3-N was observed during the study. With the exception of a NO3-N pulse during loading, solution NO3-N concentrations within and beneath both landfills remained <1 mg L−1. Concurrently, NH4-N increased to 500 mg L−1 at 0.5 m and to 7 mg L−1 at 3 m below the landfill bases. Build-up of NH4-N and lack of NO3-N in the landfills are hypothesized to result from nitrification inhibition in an anaerobic environment. Hydraulic heads showed that saturated waste resided over unsaturated soil. Formation of a hydraulically restrictive layer at the interface between the landfill contents and the underlying soil probably caused these conditions. Saturated cull-onion landfills do not appear to be a source of NO3-N contamination. Potential groundwater contamination from nitrification upon drying of landfill contents can be mitigated by removing and land-applying residual waste after sufficient degradation.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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