Simulating the Effect of Agricultural Best Management Practices on Nitrogen Leaching Using the Nitrogen Loss and Environmental Assessment Package (NLEAP) Model.

Nitrogen (N) is vital to living organisms.  Excess amounts of nitrate N (NO₃^- - N) can negatively affect water quality by stimulating excess algae growth, blocking sunlight and limiting dissolved oxygen availability to aquatic organisms.  Once NO₃^- - N leaches below a plant’s root zone, it can move down into the groundwater affecting drinking water supplies and impacting surface waterbodies.  Anthropogenic sources of N include fertilizer in urban and agricultural runoff, sewage treatment facilities, failing septic systems, and industrial facility discharges.  To reduce N loss, farms use best management practices (BMPs) including conservation tillage, cover crops, erosion control practices, and nutrient management planning.  Chesapeake Farms has progressively installed structural BMPs and initiated management BMPs to reduce the loss of N into ground and surface waters.  The objective of this research project was to analyze the effectiveness of BMPs to reduce the loss of NO₃^- - N at Chesapeake Farms over a 30-year period using the NLEAP model.  NLEAP databases with site-specific information on BMPs, soils, weather, and vegetation were developed for fields with and without BMPs.  Based on site-specific management and sources of N fertilizer used at Chesapeake Farms, NLEAP simulated water movement, water balance components, vegetative growth, and N-cycle components.  Measured and estimated data were analyzed using the paired t-Test.  The NLEAP geographic information system (GIS) extension identified areas of concern based on the model’s results.  Based on the simulation results, the NLEAP model appeared to simulate changes in land use practices and variability in weather, which affected NO₃^- - N leaching at Chesapeake Farms.  NLEAP has the potential to identify combinations of BMPs to further decrease NO₃^- - N leaching.