Simulating nitrate-nitrogen concentration from a subsurface drainage system in response to nitrogen application rates...

Area of Science:

• Agricultural Science
• Environmental Modeling
• Water Quality

Background:

• Computer models are crucial for assessing agronomic impacts on nitrogen (N) dynamics in drained fields.
• Previous evaluations have not fully assessed model accuracy in capturing nitrate-nitrogen (NO3-N) variability across diverse N application rates.
• Potential errors in simulating other system components may affect model performance.

Purpose of the Study:

• To evaluate the performance of the Root Zone Water Quality Model 2 (RZWQM2).
• To assess RZWQM2's ability to simulate the response of NO3-N concentration in subsurface drainage to varying N application rates.
• To validate model predictions against long-term field data.

Main Methods:

• Utilized a 16-year field study in Iowa (1989-2004) with nine N rates (0-252 kg N ha(-1)).
• Employed RZWQM2, previously calibrated with data from 2005-2009 at the same site.
• Evaluated model performance using Nash-Sutcliffe efficiency, ratio of root mean square error to standard deviation, and percent bias.

Main Results:

• RZWQM2 demonstrated satisfactory performance in simulating NO3-N concentration responses to N fertilizer rates.
• Key performance metrics included Nash-Sutcliffe efficiency (0.76), RMSE/SD ratio (0.49), and percent bias (-3%).
• Model simulations accurately predicted the N application rate needed to meet the maximum contaminant level for annual average NO3-N.

Conclusions:

• RZWQM2 shows reliable performance in simulating NO3-N concentrations in subsurface drainage across a range of N application rates.
• The model's accuracy is supported by its satisfactory statistical performance metrics.
• RZWQM2 is a valuable tool for predicting NO3-N in subsurface drainage when locally calibrated.