Improved chamber systems for rapid, real-time nitrous oxide emissions from manure and soil

Authors: Parker, David; Todd, Richard; Waldrip, Heidi; Webb, Kathleen; Willis, William - Will; Meyer, Beverly; Marek, Gary; CASEY, KENNETH - Texas A&M Agrilife; AUVERMANN, BRENT - Texas A&M Agrilife; MAREK, THOMAS - Texas A&M Agrilife; PEMBERTON, BRIAN - Texas A&M Agrilife

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2017
Publication Date: 8/29/2017
Citation: Parker, D.B., Todd, R.W., Waldrip, H., Webb, K., Willis, W.M., Meyer, B.E., Marek, G.W., Casey, K.D., Auvermann, B., Marek, T., Pemberton, B. 2017. Improved chamber systems for rapid, real-time nitrous oxide emissions from manure and soil. Transactions of the ASABE. 60:(4)1235-1258. doi:10.13031/trans.1215a.

Interpretive Summary: Improved system for quantifying greenhouse gas emissions from manure. Nitrous oxide is a greenhouse gas emitted from cattle manure and soils. Nitrous oxide has a global warming potential about 300 times higher than carbon dioxide. Nitrous oxide emissions have traditionally been measured using closed chambers. However, these earlier methods rely on three or four gas samples collected over a period of 30 to 60 minutes and are very labor and time intensive. Therefore, scientists from USDA-ARS (Bushland, Texas) and Texas A&M AgriLife Research (Amarillo, Texas) developed an improved method to accurately quantify nitrous oxide emissions from manure and soil in only 30 seconds. The improved method relies on a real-time, continuous nitrous oxide analyzer. The analyzer determines nitrous oxide concentration every second with precision lower than one part per billion. The improved method will result in more accurate and precise estimates of greenhouse gas emissions from manure and soil.

Technical Abstract: Nitrous oxide (N2O) emission rates have traditionally been measured using non-flow-through, non-steady-state (NFT-NSS) chambers, which rely on measuring the increase in N2O concentration in the sealed chamber headspace over time. These flux measurements are very labor and time intensive, requiring three to four gas samples collected over a 30 to 60 minute period, followed by laboratory N2O measurement with a gas chromatograph (GC) and flux rate calculation. The objective of this research was to develop and evaluate improved, real time NFT-NSS flux chamber designs that rapidly quantify N2O emissions from manure and soil. The first chamber system consisted of six square chamber bases with surface area of one square meter. The chamber bases were mounted on a rail system to facilitate controlled indoor and outdoor laboratory research at a pilot scale. An aluminum lid was moved among the chamber bases. A second portable chamber system with a circular footprint (0.49 meter internal diameter) was designed for use in field measurements. With both systems, N2O concentrations were measured each second with 0.1 parts per billion precision by recirculating sample air through a real time continuous N2O analyzer with return flow into the chamber. Performance and observational data are presented for different chamber vent designs, sealing mechanisms between the chamber base and lid, recirculation pumps, and presence or absence of an internal fan that mixes headspace air within the sealed chamber. Ten consecutive flux measurements were obtained using moist manure within a 15 minute period, where chamber bases were fitted with lids for 60 seconds and removed for 30 seconds. The mean calculated N2O flux was 43.1 milligrams per square meter per hour. Using dry manure, five consecutive flux measurements showed a very low, but consistent, flux that averaged 0.025 milligrams per square meter per hour. Five case study experiments demonstrated the usefulness of these chamber system and highlight discoveries and lessons learned to enhance future research efforts. Major discoveries and observations included: 1) installation of a small internal fan within the chamber lids decreased N2O fluctuation over small time periods, allowing for precise measurement of manure N2O fluxes as low as 0.0073 milligrams per square meter per hour; 2) two distinct N2O peaks were observed at 1 and 21 days following the addition of water to manure, with the second peak accounting for 83 percent of the total N2O emitted over 45 days; and 3) there was notable diurnal variation in N2O fluxes due to temperature variation even when manure was dry. These flux chamber systems proved to be more rapid, precise and repeatable than traditional GC-based NFT-NSS flux chamber methods, and offer promise for future greenhouse gas emissions research on manure and soil.