Quantifying Sources of Variation in Denitrification in Agricultural Landscapes
Southeast Watershed Research
Project Number: 6048-13000-026-07
Specific Cooperative Agreement
Start Date: Sep 01, 2014
End Date: Sep 30, 2017
To develop and apply new denitrification measurement and scaling approaches to sites in the USDA Long Term Agricultural Research (LTAR) network. Specific questions that we will address include:
- Are these new measurement methods sensitive enough to detect differences in denitrification within and between specific crop fields, offsite areas and different regions?
- Can we develop experimental designs to account for the key soil, vegetation and hydrologic properties that influence denitrification at these different scales?
- Will new sensor-based approaches to temporal scaling provide strong enough relationships between denitrification and soil oxygen, water and temporal to provide a strong basis for temporal scaling of activity?
- Can evaluations of spatial and temporal variability be used to develop recommendations about sampling methodologies, instrumentation and inferences that can be drawn from sampling at different spatial/temporal intensities across the LTAR network?
- Can measurements of denitrification and nitrous oxide:nitrogen gas help to guide efforts to quantify in situ emissions of nitrous oxide across the LTAR network, e.g., how can placement of cavity-ring-down spectrometers, flux towers and traditional chamber methods be most effectively deployed to account for potential “hotspots” and “hot moments” of nitrous oxide emissions?
The cooperator will work with USDA ARS scientists to generate hypotheses about key sources of spatial variation in denitrification at the sites. Key factors that will be considered will include soil texture, presence of confining layers and/or perched water tables, soil organic matter levels, slope, cropping system and fertilization practices. They will then select a relatively large number of locations (40 – 50 per site) for measurements of denitrification potential. These measurements will be used to define a smaller number (4 – 8) of functional classes for measurements of actual denitrification rate. Sensors for continuous measurements of soil oxygen, moisture and temperature will then be established in these classes and actual denitrification rates will be measured 2 to 4 times in the growing and dormant seasons. Sensor data and geographic estimates of the areal coverage of the different functional classes will then be used to produce watershed-scale estimates of denitrification. These estimates will be compared with watershed nitrogen balances and nitrous oxide and/or carbon dioxide emission data where available.