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Quantifying Annual Nitrogen Loss to Groundwater Via Edge-of-Field Monitoring: Method and Application.
Michael Cardiff1, Laura Schachter2, Jake Krause3
1Department of Geosciences, University of Wisconsin-Madison, Madison, WI, USA.
Ground Water
|June 1, 2022
Summary
Modern agriculture significantly impacts water quality through nitrogen loss. This study introduces a minimally invasive method using edge-of-field monitoring and tracer application to quantify annual nitrogen leaching to groundwater from agricultural fields.
Area of Science:
- Environmental Science
- Agricultural Science
- Hydrology
Background:
- Agricultural practices are a major source of nitrate pollution in water bodies.
- Understanding field-specific nitrogen loss is crucial for effective environmental management.
- Current methods for assessing nitrogen loss can be invasive and hinder farmer adoption.
Purpose of the Study:
- To develop and apply a minimally invasive method for assessing annual nitrogen loss to groundwater at the agricultural field scale.
- To quantify nitrogen leaching from a commercial agricultural field over a five-year period.
- To identify optimal conditions for reliable mass flux estimation of nitrogen loss.
Main Methods:
- Edge-of-field monitoring using multilevel samplers.
- Annual application of a bromide tracer injected at the water table.
- Calculation of nitrogen loss using spatio-temporal integrals of measured concentrations.
- Laboratory analysis of nitrate concentrations for accuracy.
Main Results:
- Nitrogen losses from the studied field were comparable to or slightly below reported values for similar crops.
- Over 25% (>60 kg/ha) of applied nitrogen leached to groundwater annually.
- Method reliability was highest with direct tracer injection at the water table and laboratory nitrate analysis.
Conclusions:
- The developed method provides a practical approach to quantify field-scale nitrogen loss to groundwater.
- Significant nitrogen leaching occurs even with seemingly moderate application rates.
- Accurate laboratory analysis and direct tracer injection are key for reliable nitrogen loss assessments.
