Automated Sampling Strategies to Account for Temporal and Spatial Variability of Soil N2O Emissions.

Continuous flow through chamber systems are recognized for their superiority in obtaining high resolution seasonal greenhouse gas emissions data. We combined Li-Cor 8100A CO₂ flux system with the laser spectroscopic analyzer (Los Gatos Research Inc, Mountain View, CA) to design a robust setup for reliable concurrent measurements of N₂O and CO₂ emissions from automatic chambers and to obtain flux tower N₂O data from agricultural land. A modern off-grid power inverter allowed us to design a low maintenance compact and mobile system capable of continuous power supply to the state of the art N₂O analyzer combined with CO₂ flux instrument and climate control with substantial power consumption at over 1000W. We established a series of microplot studies with 4 chambers per treatment, soil N fertilization and additions of water on dryland and irrigated no tillage and conventional tillage cropping systems in Pacific Northwest to determine the effects of short-term events on N₂O emissions. We also ran two long-term chamber and flux tower sites consisting of 16 chambers each spread out at no tillage and conventional tillage fields, which were continuously monitored between October 2013 and October 2015. The short-term microplot studies suggested emissions were more pronounced in the tillage treatment than no-till, likely due to higher rates of organic matter decomposition and slower internal soil water drainage leading to higher cumulative N₂O and CO₂. The long-term studies at no-till and conventional tillage sites indicated emissions were similar on the yearly basis. Our studies suggest that increased number of chambers per treatment (reps) and larger field coverage, as well as measuring through prolonged periods are likely to provide results, which differ from short-term microplot studies. However, the high frequency of sampling in continuous automated N₂O and CO₂ measurement setup allows for comparison of emissions from short term events and across seasons, and establishes the basis for better understanding of emissions sources in agricultural systems.