Development of a Continuous-Flow Chamber Technique to Measure Nitrous Oxide Emissions from Agroecosystems in the Southeast.

Release of nitrous oxide (N₂O) from agricultural soils exhibits temporal and spatial variability, both of which contribute to uncertainty in quantifying N₂O emissions. The overall objective of this study is to decrease the uncertainty in N₂O emissions estimates from agricultural soils by developing a robust monitoring system that will assess the temporal variations of N₂O emissions while operating continuously and unattended in the field. The continuous system developed to date uses an infrared gas analyzer (Teledyne® Model T320U) and several flow-through chambers inter-connected via a set of solenoid valves controlled by a microprocessor. Flow rates are controlled by critical orifices mounted in common manifolds. A laptop computer running DAQ interface (DAQ Plot®, VVI Software) continuously records gas concentration and sampling location. In the current design, individual chambers (n=4) are sampled for 30-minute intervals. Ambient N₂O is measured every 2 hours. Raw measurements are further refined via Python computer code to yield average N₂O concentrations for each 30-minute interval. Preliminary results capture temporal patterns in N₂O emissions but overestimate N₂O flux in comparison to the static chamber method. Adjustments are currently being made in an attempt to minimize this apparent bias. For 2015, the system will be deployed in an organic reduced-till agroecosystem and a conventional no-till agroecosystem at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC, to determine N₂O emissions during a corn-growing season in a corn/soybean rotation. Manual static-chamber measurements will be taken after each rain event, and the data will be used in conjunction with the continuous-system data to estimate total N₂O flux for each rain event and for the entire crop season. Improvements in flow-through chamber design will continue with incorporation of advanced chambers (e.g. Li-Cor® Model LI-8100) into the overall system.