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Updated: Sep 27, 2025
08:44
Microplot Design and Plant and Soil Sample Preparation for 15Nitrogen Analysis
Published on: May 10, 2020
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Deep soil nitrogen storage slows nitrate leaching through the vadose zone.
Julie N Weitzman1, J Renée Brooks2, Jana E Compton2
1ORISE Fellow at Pacific Ecological Systems Division, Center for Public Health and Environmental Assessment, Office of Research and Development, US Environmental Protection Agency, 200 SW 35 Street, Corvallis, OR, 97333, USA.
Agriculture, Ecosystems & Environment
|April 11, 2022
Summary
Nitrogen fertilizer leaching significantly decreases with soil depth, with most loss occurring in wet fall/winter. Deep soil nitrogen accumulation requires further study for groundwater protection.
Area of Science:
- Agricultural Science
- Environmental Science
- Soil Science
Background:
- Nitrogen fertilizer is crucial for crop yield but inefficient uptake leads to environmental issues like groundwater nitrate contamination.
- Despite conservation efforts, nitrate levels in groundwater, particularly in Oregon's Willamette Valley, continue to rise.
- Understanding nitrogen (N) dynamics and leaching across soil depths is vital for mitigating agricultural impacts.
Purpose of the Study:
- To investigate the controls on nitrate leaching rates and nitrogen dynamics in agricultural soils at varying depths.
- To analyze the influence of seasonal variations and management practices, such as fertilizer input and irrigation, on N transport.
- To quantify nitrogen loss and retention within the soil profile over a four-year period.
Main Methods:
- Intensive, bi-weekly monitoring of water and nitrate transport through the vadose zone at 0.8, 1.5, and 3.0 m depths.
- Utilized lysimeters in a sweet corn (maize) field over four years to capture seasonal and annual variations.
- Calculated nitrogen leaching, crop removal, and soil retention based on measured inputs and outputs.
Main Results:
- Nitrate leaching significantly decreased with depth, showing a 54% reduction from 0.8 m (~104 kg N ha⁻¹ yr⁻¹) to 3.0 m (~56 kg N ha⁻¹ yr⁻¹).
- The majority of nitrate leaching (~72% below 3.0 m) occurred during the wet fall and winter months, despite summer irrigation.
- Approximately 29% of surface N inputs leached below 3.0 m, 44% was removed by harvest, and 27% was retained in the soil.
Conclusions:
- Nitrate leaching is depth-dependent, with substantial reduction observed in deeper soil layers.
- Seasonal water dynamics, particularly fall and winter precipitation, are primary drivers of nitrate leaching.
- Significant nitrogen retention in deep soil layers highlights the need for long-term management strategies to prevent groundwater contamination.
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