Location: Northwest Sustainable Agroecosystems Research
Project Number: 2090-11000-010-028-I
Project Type: Interagency Reimbursable Agreement
Start Date: Mar 20, 2024
End Date: Aug 31, 2031
Objective:
1. Compare nitrous oxide (N2O) and carbon dioxide (CO2) emissions under four nitrogen management strategies, including typical fall urea application, fall application with nitrification inhibitor, split fall/spring application, and compost in lieu of urea.
2. Characterize in-field and edge-of-field N2O and CO2 emissions from paired catchments with long-term no-till versus reduced-till management.
Approach:
The objectives will be addressed in two studies.
The first study will compare strategies to reduce nitrogen (N) loss and will be conducted on small plots at the Palouse Conservation Field Station in Pullman, WA. Comparisons include fall N application of liquid urea (business-as-usual), fall N application plus pronitridine nitrification inhibitor, split fall and spring application, compost application, and an unfertilized control. Nitrous oxide emissions will be monitored hourly with automated soil chambers throughout the year, except during heavy snowfall. Ancillary measures of plant biomass and soils will assess the ability of the practices to supply N during the growing season when it is needed by winter wheat crops. In-season supply of nitrate and ammonium at 5 cm depth will be measured using anion and cation resin probes (replaced weekly through April and May). In-season N demand will be measured through repeated sampling of total-N in plant biomass from late tillering through anthesis. Nitrogen use efficiency metrics will be calculated as described by Huggins and Pan (1993), employing grain N content, estimates on N mineralization from the no-N controls, and measurement of residual post-harvest soil dissolved inorganic N (DIN) to 150 cm depth. Monitoring began in October 2023 and will continue through August 2026, covering three growing seasons.
The second study will monitor N2O emissions from the Cook Agronomy Farm LTAR site in Pullman, WA, where conventional and no-till management have been compared at a small-catchment scale in 2012. This study will be conducted from 2026 to 2030. Monitoring will emphasize 1) using a flux gradient technique to measure N2O emissions at a large spatial scale; 2) capturing a greater number of rotational crops than in past monitoring; and 3) employing chambers to monitor potentially missed edge-of-field N2O emissions near the outlet of each catchment, where dissolved N and water tends to accumulate and N2O emissions are expected to be highest. In contrast to the eddy covariance (EC) method, the flux-gradient method does not require high-frequency (10 Hz) N2O measurements, and can be done with less expensive, less power-intensive N2O analyzers. We plan to measure N2O fluxes at our EC sites in each catchment using the flux gradient approach (and continue monitoring CO2 fluxes using eddy covariance). Monitoring will cover 5 harvest years of our typical winter wheat–spring canola– winter legume rotation. In addition, soil autochamber transects will be established at the outlet of each catchment, which is expected to be a hot-spot of N2O emissions. Transects will be established as soon as possible following in the spring when risk of flooding has abated. Ancillary measurements for the transects will include standard meteorological data, soil moisture and temperature at 10 cm depth adjacent to each chamber, and a soil moisture/temperate profile measured at 6 depths to 150 cm in one location near each catchment outlet.
