The Automated Bulk Sampling System (ABSS), a low-cost solution for integrated nitrous oxide emission quantification in field studies

Agricultural soils are a major source of nitrous oxide (N ₂ O), a potent greenhouse gas, but challenges in measuring its highly dynamic flux in field settings hamper modeling and mitigation efforts. We developed a remotely-deployable, high-frequency sampling system that lowers the cost of N ₂ O flux measurement and minimizes laboratory analysis. The Automated Bulk Sampling System (ABSS) is self-powered and accumulates hourly open- and closed-chamber headspace gas samples into two separate gas collection bags. The system produces two bulked gas samples at the end of the measurement period, allowing average hourly N ₂ O flux over 2-week collection periods to be estimated. Lab-based validation experiments showed high agreement between real-time analyzer and accumulated ABSS concentration readings (r ² : 0.998, bias: -0.009 ± 0.002). The system also showed high precision, or repeatability (r ² : 0.791) in field validation experiments, but an underestimation bias of 25% for N ₂ O fluxes was observed when compared to 2-week average real-time analyzer results. In exploring sources of error, we found overestimation of ambient, open-chamber samples by the ABSS to be the largest source of error (15%), augmented by underestimation of closed-chamber sample concentrations (5%). Loss of information from meteorological variation and two-point flux calculation contributed slightly to underestimation bias (6%). We used historic weather data from the U.S. Corn Belt to simulate the potential error contribution from air density variation, and found an average error of 0.049%, with the largest range in error occurring at lower fluxes. Our results demonstrate that ABSS is a valuable low-cost and low-labor solution for integrated estimates of soil N ₂ O flux in large-footprint, replicated plot experimental contexts and can help resolve critical questions in managing soil N ₂ O emissions in agricultural systems.